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Cases of the Month: Diagnosis Index

Case 130 Complex tear UT ligament with longitudinal and distal components

More recently, there has been description of a longitudinal tear of the UT ligament (along the long axis of the ligament) which may produce pain but is not typically associated with DRUJ instability. On arthroscopy these injuries are typically associated with prominent synovitis which once removed, reveals the longitudinal split within the UT ligament. In this case there was the longitudinal component accounting for the T2 hyperintensity of the ligament but also a small, distal disruption accounting for the small flap that was interposed between the triquetrum and the TFCC articular disc. At the time of surgery there was prominent synovitis about the TFCC and the flap was found and resected.

Case 129 Scapular Notching

One of the unique complications of the reverse total shoulder arthroplasty is scapular notching related to the impaction of the medial aspect of the humeral component/polyethylene along the inferior border of the scapula with shoulder adduction. The process is thought to relate not only to mechanical wear but polyethylene wear engendering an even greater degree of bone resorption. The concept has been a matter of debate for many years but with most in present day feeling that notching does correlate with increased pain and decreased performance. The grading/classification was described by Sirveaux and progresses from bone wear of the so called scapular pillar, to the inferior screw, involvement of the entirety of the inferior screw, and then involving the central screw/post or the metaglene/baseplate. Progressed degrees of notching are thought related to a greater possibility of glenoid loosening and poorer clinical outcomes.

Great efforts over the last decade have been made to try and understand how to better implant/design this prosthesis. Because of notching there is now a greater lateralizing of the center of rotation of the prosthesis and the metaglene/base plate are now placed at the far inferior aspect of the glenoid (even with inferior overhang) and with inferior tilt (often approximately 10-15 degrees). Although these changes themselves may have ramifications, at present this is working well. Interestingly as in this case when notching is seen it is often found early after the index procedure within a couple of months to one year. However, it frequently shows little progression after many years of follow up although some authors have shown substantial progress over years follow up. As there is little in terms of how to direct surgeons in the management of scapular notching, although this patient is limited she is opting for no additional surgery at this time.

Case 128 Congenital Posteromedial Tibial Bowing

Tibial bowing can be related to many underlying etiologies. The key is to recognize the direction of the apex of the bow which is how the bowing is described. Posteromedial bowing is a congenital condition, thought to be related to intrauterine positioning or a packing abnormality. It can be seen with another packing abnormality of a calcaneovalgus foot but can occur in isolation. Posteromedial bowing is considered benign because although it does frequently yield a limb length discrepancy as in this case, the bowing resolves and the overall course is much less difficult than the other causes of bowing. Anterolateral bowing is seen in congenital pseudoarthrosis either alone or in the setting of neurofibromatosis. This process is notoriously difficult to treat. Anteromedial bowing is seen in the setting of fibular hemimelia which is then associated with many other orthopedic abnormalities. Anterior bowing can be seen in a very rare syndrome called Weissman Netter syndrome or in the setting of some congenital infections or metabolic disorders such as rickets. As in this case there is frequently a marked decrease in the bowing in the first year and them a limited degree of remodeling after 4-5 years. As the proportionate difference of leg lengths remains stable through growth accurate estimates can be made to the final limb length discrepancy. Surgery is frequently performed if and when limb length discrepancies reach 2-5cm.

Case 127 Diagnosis: Aggressive Vertebral Hemangioma

Vertebral hemangioma (VH) is a very common entity seen while reading CT or MRI of the spine and especially the lumbar spine. VH are described radiographicaly as typical, atypical, or aggressive. VH pathologically have blood vessels interspersed with fatty tissue, interstitial edema, and thickened/coarsened bony trabeculae. Particularly, these thickened trabeculae account for the “polka-dot” appearance seen on axial CT images and the “corduroy” appearance seen on sagittal and coronal reformations. Typical hemangioma have a greater amount of fatty tissue giving the typical high T1 signal. The atypical hemangioma has less fatty tissue and will have less or no high T1 signal and will appear similar to many other processes with low T1/high T2 characteristics. This makes evaluation of the atypical hemangioma difficult on MRI as it can mimic many entities including metastases, myeloma, or lymphoma. However, on CT, the “polka-dot” and “corduroy” appearance will still be appreciated allowing an accurate diagnosis. The aggressive hemangioma typically has similar MRI characteristics to the atypical hemangioma but has broken through the bone and has an associated soft tissue mass. Hence on MRI these masses look very aggressive but when a CT is performed, the “polka-dot” or “corduroy” architecture is typically still able to be identified to render an accurate diagnosis. At times as in this case, aggressive hemangioma may have some fatty tissue accounting for high T1 signal but often no high T1 signal at all can be identified. Because this mass has such an aggressive appearance, biopsy is frequently performed. In fact, in this case a biopsy was performed in 2005 to help come to the appropriate diagnosis.

Case 126 Diagnosis: Osteosarcoma

This case was terrifying to me and a number of my colleagues. In looking at just the second set of radiographs, the radiolucency with sclerosis of the distal femur and the aggressive periosteal reaction would make osteosarcoma a relatively easy diagnosis. However, given the recent, normal radiographs predating the abnormal radiographs, the thought was perhaps this was more likely infection or eosinophilic granuloma. Given the unbelievably rapid progression of this process it is thought that this is going to be a very high grade malignancy but that pathology is not yet available. This case just elucidates the limitations of radiographs at times and the sometimes terrifying nature of practicing medicine.

Case 125 Diagnosis: Venous Congestion/Ischemia and Cord Edema in Cervical Spondylosis

In over ten years of putting together these cases this was one of the more fascinating and perplexing cases, I’ve had and required a great number of resources to get to the correct interpretation. In innumerable cervical spine mri’ssevere central canal stenosis is present and in cases typically with moderate or severe compression of the cord we may see a mild to moderate amount of T2 hyperintensityof the cord. It is extremely uncommon to see this very slight degree of mass effect of the cord be associated with such a massive amount of T2 hyperintensityof the cord. On initial interpretation, given the enlargement of the left side of the cord a mass was favored over cervical spondyloticchanges inducing the markedly abnormal cord.

However, after contrast administration, there is no rounded or mass like focus of enhancement but rather this vague or hazy type enhancement. Histology has been obtained in other cases where again the diagnosis has been thought to be tumor and on biopsy only inflammatory changes and findings of edema of the cord were found. This has led to the belief that in some patients with severe central canal/spinal stenosis but with only slight deformity of the cord venous hypertension/congestion is precipitated that leads to venous ischemia, a break down of the blood cord barrier/hyperpermeability, and then marked edema within the spinal cord. Interestingly, as in this case the hazy, vague enhancement has been most commonly seen at the affected disc space level. In the cases reported in the literature, patients have responded very well to decompression and our patient is to have surgery next week.

Case 124 Diagnosis: Osteopoikilosis

Perhaps not a diagnostic dilemma for many but this is a nice representation of osteopoikilosis which as seen here is manifest by multiple bone islands/areas of cortical bone within the medullary cavity or cancellous bone. The foci of cortical bone are typically centered around the joints in the ends of the bone/epiphyseal equivalents and metaphysis and parallel to the longitudinal axis of the bone. This is an incidental finding of no significance but as to otherwise appreciate that there is no more aggressive process at hand.

Case 123 Diagnosis: Tensor Fascia Latae Pseudomass

A rare diagnosis and frankly one I did not know existed until this case. Found typically in older women it is thought to arise in the setting of abnormal gait that produces a hypertrophy of the tensor fascia latae. It is most typically found in the setting of total hip arthroplasty with deficient hip abductors. Although no arthroplasty is present in this case, there is clear deficiency of the hip abductors. The thought is that there is a compensatory hypertrophy of the tensor fascia latae to accommodate/mitigate the effects of the deficient hip abductors.

Case 122 Diagnosis: Anteromedial Meniscofemoral Ligament

Different than many of the cases presented in the past the area in question represents a normal, albeit rare variant. Important in this situation so as the surgeon does not mistake this process for a displaced fragment of meniscus. Well known is the transverse meniscal ligament extending from the anterior horn of the lateral meniscus to the anterior horn medial meniscus. Infrequently an oblique meniscal meniscal or intermeniscal ligament can be seen. This extends from the anterior horn of one meniscus to the posterior horn of the other and is named for the anterior horn attachment on the medial or lateral side. The ligament shown here is the most uncommon normal variant.

This ligament also sometimes called the anterior meniscofemoral ligament extends along the course of the ACL to insert into the anterior horn of the medial meniscus. It looks similar to the infrapatellar plica or ligamentum mucosum but does not run into Hoffa’s fat pad/inferior pole of the patella. We typically think of only two structures in the notch, the ACL and PCL. Anything else we think is going to be a displaced mensical fragment but these normal, variant ligaments also need to be entertained. A helpful clue often is that there does not seem to be a deficiency of any meniscus to be the donor site but also keeping in mind normal variant anatomy is crucial.

Case 121 Diagnosis: Subchondral Fracture

The very subtle area of irregularity of the femoral head represents a subchondral fracture. There is typically as shown here a marked amount of edema even in the setting of the very subtle deformity. Patients typically have marked pain and difficulty with activity. It is my belief as well as many others that the concept previously described as transient osteoporosis of the hip in fact represents these very subtle subchondral fractures. In years past, we were limited by resolution to see these very subtle fractures but given current techniques and equipment these subtle fractures can now be seen.

Interestingly, in this case the patient had an outside MRI that was read as necrosis. Areas of AVN do not have a striking degree of edema unless they have collapsed or are collapsing. In that situation, again there is subchondral fracturing that is precipitating the edema. In a subchondral fracture or AVN with collapse, the marked edema relates to fracture of the bone. This patient is being treated with crutches as well as a metabolic analysis and will be rescanned to assess for healing.

Case 120 Diagnosis: Oncogenic Osteomalacia

Osteomalaciacan be produced by numerous causes but one in particular relates to neoplasms that secrete fibroblast growth factor 23 which inhibits phosphate resorption in the kidney and produces osteomalacia. These tumors are classified as phosphaturicmesenchymal tumors (PMT) and the most common is a soft tissue hemangiopericytoma. As in this case there is often a protracted course and marked disability. The osteomalaciacauses repetitive episodes of fracturing which leads to the marked sclerosis of the bone and in this case varusdeformity of the femoral necks.

The findings on the MRI of the bone and the soft tissue mass are classic for this rare diagnosis. Octreotide works as a somatostatin analog that binds to somatostatin receptors frequently in neuroendocrine tumors as well as in the PMTs.Octreotide shows normal uptake in the liver, spleen, kidneys/urinary tract, and bowel. Variable uptake is present in the thyroid and pituitary. In addition, newer Ga isotopes with PET CT are being utilized to localize these tumors which can often be small and not clinically recognizable. This patient is to undergo removal of the soft tissue mass.

Special thanks to Robert Schneider MD, Douglas Mintz MD, and Alissa Burge MD for their assistance in this case.

Case 119 Diagnosis: 4th/5th Carpometacarpal Dislocation

The most common of the CMC fracture dislocations involve the small and then ring fingers. These articulations are more mobile than the remainder of the articulations and particularly the pull of the ECU attachment at the base of the fifth metacarpal makes these locations most susceptible to injury. Invariably there is dorsal displacement of the metacarpals. There is typically impacted fracturing along the dorsum of the hamate and at times as in this case along the dorsum of the capitate.

As was mentioned previously, on the CT examination this is not a diagnostic dilemma. However, this case again underscores the necessity for at the least orthogonal radiographs for adequate assessment. In addition, this shows how radiographs at times can underestimate/belie the overall extent of injury. Well delineated is the importance of understanding typical presentations of pathology and the need for further imaging for confirmation and as in this case, preoperative planning.

Case 118 Diagnosis: Stener Lesion

Perhaps not a diagnostic dilemma on this case but a nice representation of a Stener lesion. The UCL is torn when a valgus force is imparted to the thumb as when holding a ski pole when falling and hence the term skier’s thumb. When gamekeepers would break the necks of small animals such as rabbits the repetitive motion would cause scarring of the UCL and hence a chronic analagous process is now often referred to as gamekeeper’s thumb. The architecture of the collateral ligaments in the hand and foot are complicated with proper and accessory components. In the Stener lesion typically both components are disrupted although typically on imaging we do not separate the individual components. In a Stener lesion, the adductor aponeurosis or the slip of tissue of the adductor pollicis that continues distal to the proximal phalangeal attachment to join the extensor apparatus, lies inward or deep to the UCL.

The aponeurosis blocks the ligament from apposition to the underlying bone and hence does not allow ligament healing. Without repair there is a loss of strength of the thumb and typically precipitated early arthritis. As in this case, the injury is often not a simple valgus moment and the RCL is frequently injured. Additionally, the adductor myotendinous unit is often frequently injured. Stener lesions or UCL ligament injuries with clinical and radiographic evidence of instability are indicated for surgery.

Case 117 Diagnosis: Post traumatic Pneumothorax

As compared to many of the cases we have shown this case is much more of an "eye test". The findings particularly on the radiographs although difficult can be made and are imperative. More frequently present in the setting of rib fractures with a clavicle fracture as in this case, isolated clavicle fractures can also rarely present with a pneumothorax. Given the size of the pneumothorax this patient underwent chest tube decompression with re-expansion of the lung and then subsequent clavicle fracture fixation.

Case 116 Diagnosis: Post Chemotherapy changes in the setting of B Cell Lymphoma

The multiple destructive, FDG avid lesions is typical of a metastatic process but otherwise nonspecific. The striking finding in this case is that the patient finished their chemotherapy regimen only three months prior to the 12/2017 CT study in 9/2017. This rapid reconstitution of bone is a well known phenomenon, emphasizing the amazing healing potential of the human body as the glenoid albeit slightly abnormal is well reconstituted. The marrow pattern on MRI typically shows marked changes following chemotherapy in those patients who have a good response to treatment. No post treatment MRI exams were available at the time this case presentation was prepared.

Case 115 Diagnosis: Metallosis

As has been discussed recently in the orthopedic and radiology literature is the concept of adverse local tissue reaction comprising the phenomenon that occur in the setting of metal on metal bearing interactions. This incorporates the issues of a lymphocytic or ALVAL response related to metal ions and metal debris engendering a histiocytic foreign body reaction and producing metallosis. Both of these processes are more typically seen to involve the soft tissue but as seen in this case can also destroy the underlying bone and may cause a loosening of the prosthesis.

In this case the implant had a metal cup with a composite metal and polyethyelene liner that became displaced allowing wear of the poly liner and the metal liner. The metal liner impinged upon the neck almost transecting the neck and in the process produced a huge amount of metallic debris. This metallic debris on radiographs can be seen as amorphously dense tissues often referred to as a cloud sign or may cause a dense, linear staining of the wall of the collections producing a metal line sign at the periphery of the mass. Similar findings are seen on CT examination but become more conspicuous and CT allows for better demonstration of the bony destruction. On MRI, metallosis typically produces markedly low signal intensity tissue. This can be seen in isolation or frequently with findings of an ALVAL response and a polymeric wear induced synovitis.

Case 114 Diagnosis: Tethered cord/tight filum syndrome

The conus medullaris terminates above the L2-L3 disc level in greater than 98% of people and a conus terminating below this is considered low lying. A low lying conus relates to a failure of normal superior migration of the filum terminale. This subsequently yields a thickened filum defined as greater than 2mm at its midpoint or greater than 1mm at the L5-S1 level. Frequently as in this case the low lying cord is associated with fatty infiltration which can either be a tubular, fatty fibrolipoma or a focal mass or so called terminal lipoma.

A tethered cord can either be discovered in children or in adults but the symptoms associated with this finding are frequently different. Many adults present with pain frequently following activity and leg weakness which are not typical in children. Both adults and children may have urologic symptoms or paresthesias.

Case 112 Diagnosis: HO from long standing immobility

This patient had an episode of sepsis precipitating a coma and from the long standing immobility he developed a marked degree of heterotopic ossification. Following coma and in patients with burns and long standing immobility, if the patients are not moved frequently enough heterotopic ossification will form and may lead to ankylosis of joints or other restriction of movement. Not shown in this case but also an entity to be weary of is HO with subsequent destruction of the bone. This is often seen about the ischial tuberosities and indicates a decubitus ulcer extending down to and destroying bone.

Case 113 Diagnosis: Chondroblastoma

Chondroblastoma is an almost always benign mass that occurs in younger patients typically between 10 and 25. It is part of the differential of an end of the bone lesion that includes infection, geode, giant cell tumor, and clear cell chondrosarcoma. The well demarcated nature of this lesion, the areas of probable punctate calcification (which as in this case can be difficult to see on radiographs), the prominent surrounding marrow edema pattern of the bone, and the fluid fluid levels would strongly suggest a chondroblastoma. Fluid fluid levels can be seen in many entities such as ABC, giant cell tumor, fibro-osseous lesions, and telangiectatic osteosarcoma and indicate blood/fluid contained spaces. Surgical treatment with curettage and packing is to be performed on this patient.

Case 112 Diagnosis: HO from long standing immobility

This patient had an episode of sepsis precipitating a coma and from the long standing immobility he developed a marked degree of heterotopic ossification. Following coma and in patients with burns and long standing immobility, if the patients are not moved frequently enough heterotopic ossification will form and may lead to ankylosis of joints or other restriction of movement. Not shown in this case but also an entity to be weary of is HO with subsequent destruction of the bone. This is often seen about the ischial tuberosities and indicates a decubitus ulcer extending down to and destroying bone.

Case 111 Diagnosis: Meniscal Ossicle

Meniscal ossicles are foci of bone that are present within the meniscus and have a shape that conforms to the meniscus. Their etiology has been debated as degenerative, post traumatic, and congenital/developmental. The most favored diagnosis at this time is post traumatic given their frequent position within the posterior horn medial meniscus and frequent association with ACL injuries and cartilage wear. The recognition of the ossicle as compared to otherwise a potential loose body or avulsion fracture is probably the most important point. Although there are reports of surgery for a meniscal ossicle that more so relates to surgery to an underlying meniscal tear and not the ossicle per se. The anterior ossification/calcification in this case is likely post traumatic and not within the meniscus.

Case 110 Diagnosis: Sickle Cell Disease

A full discussion of the pathology of sickle cell disease is beyond the scope of this presentation. Suffice to say it is related to abnormal hemoglobin that causes a sickling of the red blood cells and precipitates infarcts of various end organs. This is seen in the bone as well as the spleen. In addition, there is an increased degree of erythropoietic marrow to help combat the anemia of sickle cell disease and hence the diffuse abnormal signal on MRI. The more diffuse sclerosis is thought to relate to either multiple infarcts of the bone or end stage fibrosis/mineralization.

The breakdown of the red cells also produces a lot of bilirubin that can form gallstones and often necessitates cholecystectomy. There is an increased risk of thromboembolic disease in these patients that is multifactorial but often necessitates placement of an IVC filter particularly before an orthopedic procedure. Related often to the infarction of the spleen as well as decrease marrow available for production of white blood cells, these patients are at a great risk to develop infections of all sorts.

Case 109 Diagnosis: Tibial Tray Spinout

Tibial tray spinout is an uncommon but known complication that can occur in the setting of a mobile bearing TKA with a rotating platform. As in this case it is seen much more common in the PCL sparing devices and often in those patients that have a preoperative valgus knee. The dislodging and rotation of the poly tray typically occurs early in the postoperative setting unless the underlying sot tissue envelope is poor in which case it may occur later. The etiology is not completely understood but may relate to necessary gap balancing in the valgus knee. The inciting event is often an adduction movement on a semiflexed knee.

Clearly a big key to the diagnosis is the clinician/surgeon having insight that this is the underlying pathology so as to help focus one’s attention on the imaging. As seen here is the change from the normal prominence of the poly tray from anterior to posterior and malalignment of the femur relative to the tibia. Particularly the axial CT images make the rotation of the tray dramatic and conspicuous.

Case 108 Diagnosis: Disruption of middle or central slip of the IST

The infraspinatus tendon is one of many tendons that is multipennate in architecture. Although there can be variation there are typically three tendon slips. A tendinous or musculotendinous disruption of the middle or central slip is an uncommon cuff tear. The remainder of the tendon slips remain intact. As attention is typically drawn to the bony attachment or critical zone of the SST and IST it is important to not overlook this more medial process.

In the literature this process is more typically described at the myotendinous junction and indeed some disruption occurs there. However, the vast majority of the pathology in this case and in the limited number of cases at our institution have involved the tendinous attachment with marked medial displacement. The thickness of the tendon relates to underlying tendinosis as well as the recent trauma.

Case 107 Diagnosis: Cystic Adventitial Disease of the Popliteal Artery

A rare entity and infrequently encountered in musculoskeletal imaging. This disease is most frequently found in men 40-50 years of age that present with increasing pain with activity or intermittent claudication. The cysts yield compression of the popliteal artery in a number of patterns. This process can be treated by multiple surgical procedures typically separated at attempt to remove or evacuate the cysts or resect the vessel and performing direct anastomosis or graft interposition. Another entity that has to be distinguished is popliteal entrapment syndrome.

Popliteal entrapment syndrome can have multiple causes as well but most frequently relates to an abnormal or variant course of the medial head of the gastrocnemius. With activity, this leads to increased compression of the popliteal artery. With plantar flexion and contraction of the gastrocnemius, there would be expected increased compression of the popliteal artery.

Case 106 Diagnosis: Myxoinflammatory Fibroblastic Sarcoma (MIFS)

MIFS is a malignant neoplasm frequently found along the distal extremities with extension along fascial planes and particularly may extend along/about tendon sheaths and neurovascular bundles. The myxoid component causes the markedly high T2 signal intensity. The enhancement pattern can be variable often depending on the degree of de-differentiation of the neoplasm. The extension along tissue planes generates a "tail of tissue" that frequently leads to wide excisions and likely the high recurrence rate associated with this neoplasm. Although many soft tissue tumors are difficult to differentiate the somewhat unique characteristics of this neoplasm make prospective diagnosis prior to surgery possible.

Case 105 Diagnosis: High-grade osteosarcoma

The patient underwent open biopsy with the diagnosis confirmed. Whenever there is density of the bone the thought of bony matrix in the setting of a bone producing tumor must be entertained. This can be seen in osteoblastoma or in osteosarcoma. Bony matrix in the soft tissue should bring up the idea of an extraskeletal osteosarcoma which is extremely rare and not being presented here. The more destructive portion of the tumor is in keeping with the aggressive nature of the lesion. Frequently underutilized is the role of assessing the marrow with the use of Houndsfield measurements. Be it in fatty or erythropoietic marrow, the normal adult marrow should have a fat attenuation value. The soft tissue attenuation values indicate a mass replacing the normal marrow. In this case, small masses are also present in the lung representing metastatic foci.

Case 104 Diagnosis: Freiberg Infraction

Freiberg Infraction is a well known but poorly understood process most commonly affecting adolescent to teenage women. It most frequently involves the second MT head with the third being much less commonly involved. The etiology is thought to be multifactorial, perhaps related to chronic trauma, vascular insult, underlying abnormal alignment, and genetic predisposition. It is frequently characterized in the nebulous realm of osteochondrosis. Early on in the process there may be a subtle subchondral fracture that goes on to collapse of the dorsal and then plantar aspect of the metatarsal head.

This collapse of the bone precipitates the marked edema of the bone. As the process progresses there is then extensive cartilage loss and arthritis yielding the marked degree of synovitis shown in this case. Early on in the disease process, conservative management may be tried but operative management is necessitated at the later stages of the disease.

Case 103 Diagnosis: Discal cyst

Discal cyst is one of many cysts or cyst like masses that can be present in the lumbar spine. Much more frequent are perineural/Tarlov cysts or synovial cysts emanating from the facet joints. Additionally, at times peripheral nerve sheath tumors can be so T2 hyperintense to look like a cyst. One technical point in this case is that these findings are subtle and as such obtaining images as orthogonal to the disc space or motion segment becomes imperative. The localizer sequence was to indicate that obtaining an additional pulse sequence angled particularly to L5-S1 can be extremely helpful. The etiology of a disc cyst is still debated and likely relates to a cystic degeneration of a disc herniation and that is why demonstrating continuity of the cyst to the disc tissue is important. Alternative theories of etiology relate to hematoma with subsequent liquefaction. As in this case, the cyst may cause mass effect upon neural elements necessitating intervention.

Case 102 Diagnosis: Soft tissue chondroma

Soft tissue masses can either be readily diagnosed such as lipoma or peripheral nerve sheath tumor, completely nonspecific in nature, or may have characteristics suggesting but not definitive for the mass. This mass falls into the latter from an imaging standpoint. Cartilage lesions typically have high T2 or high proton density signal with a lobulated architecture. Cartilage lesions are frequently found in the medullary aspect of the bone as enchondroma which typically does not require contrast for diagnosis. Therefore, the post contrast appearance is not as familiar but this case does show the typical post contrast architecture of a cartilage lesion with peripheral enhancement and enhancement of septa of cartilage cells through the mass.

This case also highlights typical features of a soft tissue as compared to a bony mass where the epicenter of the mass is within the soft tissue, there is a bowing or beveling of the cortex toward the medullary aspect of the bone, and an absent periosteal reaction. The indolent remodeling of the bone indicates a long standing process which is most likely benign but could be seen in a low grade malignancy. In this case although a cartilage lesion was prospectively entertained, pain as well as the difficulty in excluding a low grad chondrosarcoma necessitated surgical removal.

Case 101 Diagnosis: Sarcoid

Sarcoid is a poorly understood granulomatous disorder that can involve every organ system of the body. It is stated that anywhere from 1 to nearly 15% of people that have sarcoid will show bony manifestations. The bone, skin, soft tissue (particularly periarticular), joints, and muscle can all be affected by this disease. In the small bones of the hands and feet there is a classically described reticular or lace like pattern seen but this is not present in this patient. There can also be large cystic lesions, sclerotic lesions, or a conglomeration of small cystic lesions. In the larger bones as seen here there are frequently focal masses but a more infiltrative or diffuse pattern can be seen.

On MRI, the soft tissue masses are frequently described as low T1 and high T2 but the T2 can be somewhat variable in nature. Similarly, the large lesions of the bone are typically high on T2 but may be variable in nature. The signal intensity is thought to relate in some degree to the activity of the process. Although multiple osseous lesions should always raise the suspicion of metastatic disease, this case highlights that other etiologies always have to be thought about as alternative diagnoses.

Case 100 Diagnosis: Oblique meniscomeniscal ligament

Many normal variants are seen of the menisci and particularly well known are the attachments of the transverse meniscal ligament and meniscofemoral ligaments. Much less common but important to recognize is the oblique meniscomeniscal ligament that extends from the posterior horn of one meniscus to the anterior horn of the other meniscus. This yields a band of tissue that extends along the intercondylar notch and can be confused for a bucket handle fragment. However, in the case of the ligament, the meniscus is not deficient and the band of tissue runs between the ACL and PCL where as if there was a bucket handle tear, the donor meniscus would be abnormal and deficient and the band of tissue is seen adjacent to but not between the cruciate ligaments.

This case does have an underlying medial meniscal tear with a superiorly displaced fragment towards the notch which can make things confusing for the radiologist and arthroscopist. It is imperative to alert the arthroscopist to the two different processes so that only pathologic tissue is treated/resected and the normal structures are not resected.

Case 99 Diagnosis: Lesser MTP joint instability

MTP joint instability typically occurs in middle aged women and involves the second MTP most frequently and less so the third and remainder of the MTP’s. Predisposing factors relate to an elongated metatarsal as well as wearing high heels and shoes with a narrow toe box. The pathology tends to occur in a typical progression with first degeneration and early tearing of the lateral aspect of the plantar plate at its insertion to the proximal phalanx of the toe. This insertion is a conjoined insertion of the plantar plate and lateral collateral ligament. With further injury, there is scarring and contracture of the medial capsule and dynamic stabilizers. This helps render the medial subluxation of the proximal phalanx relative to the metatarsal. With progressive degeneration, there is a complete disruption of the plantar plate that yields a dorsal subluxation/dislocation of the proximal phalanx relative to the metatarsal.

As a part of the injury of the lateral structures, there can be a marked amount of scarring that will be present about the deep intermetatarsal ligament that can mimic a Morton’s neuroma. However, this scarring tends to be asymmetric relative to the webspace as compared to centered more directly on the webspace in the setting of neuroma. This difference is important as relates to treatment and prognosis for the two different entities. In this situation, a shortening metatarsal osteotomy was performed and can be combined with soft tissue balancing/other osseous procedures deemed necessary or preferred by the treating physician.

Case 98 Diagnosis: Distal radial fracture with slight dorsal displacement/prominence at the level of Lister’s tubercle

The extensor pollicis longus tendon demonstrates an intrasubstance partial tear and then becomes completely disrupted at the area of bony irregularity of Lister’s tubercle. The extensor pollicis longus (EPL) tendon demonstrates an intrasubstance partial tear and then becomes completely disrupted at the area of bony irregularity of Lister’s tubercle.

The EPL is the most common disrupted tendon in the setting of distal radial fracture and is related to friction/and irregularity as the tendon rubs against the irregular margin of the fractured Lister’s tubercle. As the tendon is the sole source of extension of the IP joint of the thumb it frequently necessitates repair or tendon transfer.

Case 97 Diagnosis: Medial clavicle apophyseal injury

Serendipity view shows symmetric alignment of the sternoclavicular (SC) joints. CT study is slightly limited as the study was initially protocolled for a shoulder study and to prevent against rescanning the patient retro-recon images were post-processed. The SC joints are symmetric in position with soft tissue swelling about the right SC joint. The MRI shows an apophyseal injury of the right medial clavicle with partial disruption of the capsule but no displacement of the apophyseal plate. The SC fibrocartilage disc/meniscus has sustained a low grade injury but is also not posteriorly displaced.

Sternoclavicular joint injuries are uncommon but frequently involve an anterior dislocation. In the setting of a higher energy mechanism a posterior dislocation can be caused. This is of importance because with posterior displacement there can be impingement upon the great vessels in the mediastinum. The medial clavicular apophsyis is not mature until the early to mid 20’s and in the skeletally immature patient the apophysis is typically the site of injury. As the apophysis is not able to be perceived on radiographs or CT, those modalities will show a normal alignment. Only MRI can show displacement of the apophysis and articular disc which are imperative to evaluate as particularly posterior displacement could lead to cosmetic deformity as well as the aforementioned impingement of the great vessels.

Case 96 Diagnosis: Displaced poly liner

The history withheld in this case is that immediately prior to the radiographs and CT of 3/30 the patient had sustained a dislocation with relocation. This case shows the importance of trying to stay current on the hardware that is being used. The Dual Mobility Cup (DMC) is a type of arthroplasty that is utilized for individuals that are thought to be a dislocation risk following total hip arthroplasty. However, when there is a dislocation of the hip in the setting of a DMC with relocation there is a known risk of dislodging of the poyethylene liner which is what occurred in this situation.

The geometric, low attenuation mass is the displaced polyethylene liner. This can not be seen on the radiographs because it is sitting directly posterior to the metal components of the hip. A frog leg lateral view was also done but not shown in this case and it too did not show the liner. The key is to realize that in the setting of a DMC with a dislocation and relocation, an asymmetric positioning of the femoral component indicates there has been a displacement of the liner. This prompted the CT to look for the liner. The CT also showed the bone fragments of the posterior wall that are unlikely to represent heterotopic ossifcation related to the recent arthroplasty and much more likely related to a recent dislocation. The patient was subsequently revised to a different type of prosthesis with a constrained acetabular liner again to help prevent against dislocation.

Case 95 Diagnosis: Juxtacortical chondroma

Juxtacortical chondroma also referred to as periosteal chondroma or surface chondroma is a benign cartilage tumor typically found in young adults in the proximal humerus or femur in the metaphysis or occasionally as in this case of the finger. Typically they present with a thickened, or heaped up adjacent periosteal reaction. They then have similar characteristics to other benign cartilage tumors with punctate or ring and arc calcification on radiographs or CT and then prominent hyperintensity on more T2 weighted pulse sequences as well as a multilobulated architecture. Punctate areas of calcified cartilage matrix can be appreciated by areas of markedly low signal intensity/signal void on all pulse sequences

Although a benign, process they are typically resected as they can be painful and there is frequently difficulty even on histology between differentiating a juxtacortical chondroma and a juxtacortical chondrosarcoma, which are typically low grade malignancies. A larger lesion of greater than 3 cm and more irregular or permeative characteristics to the lesion on imaging are typically more in favor of a malignant process.

Case 94 Diagnosis: Tricep injury

A more general term is given for this diagnosis than most because shown is a spectrum of injury from strain to partial to complete disruption. Particularly in the first case, the ossification may represent heterotopic ossification from injury but the timing and suggestion of a donor site favors avulsion of an enthesophyte. Even in the setting of an avulsed enthesophyte, the attached tendon or ligament typically sustains a degree of injury and hence will not appear normal on MRI exam. Except in the setting of very high force injury, normal tendons and ligaments tend not to be disrupted. Therefore, in the setting of trauma to a ligament or tendon, the underlying architecture of the structure is typically heterogeneous related to underlying pathology as well as the recent injury.

The triceps insertion is actually a superficial tendinous attachment of the long head and lateral head and a deep muscular attachment of the medial head. As is shown in these cases, there can be varying involvement of both heads and varying degrees of residual function. The degree of injury and functional needs of the patient also drive whether or not surgery is required or not. In the first case, the enthesophyte was removed with the injured tendon directly attached to the bone via a bioabsorbable fixation device.

Case 93 Diagnosis: Neurofibromatosis type I (NF1)

In this case, no reason was found for the patient’s new symptoms but the case presentation was to demonstrate NF 1. A dysplasia of mesodermal and neuroectodermal tissue it has a much greater tendency to involve the periphery than its counterpart, NF2. In the musculoskeletal system we may see a sharply angled curve of scoliosis; tibial bowing with pseudoarthrosis; multiple lesions of the bone related to erosion from soft tissue neurofibroma, underlying mesodermal dysplasia, or non-ossifying fibroma; dural ectasia with vertebral body scalloping; unilateral limb overgrowth; and as in this case plexiform neurofibroma.

Plexiform neurofibroma are pathognomonic for NF1 but are not always present. As in this case, they are large, multilobulated masses that often arise from major or named nerves. In the subcutaneous soft tissue they present as a “bag of worms” architecture that can be appreciated particularly from the coronal images. The plexiform name takes its origin from its histopathology where there is a plexus of proliferating neural tissue. These tumors have a predisposition for malignant transformation and are difficult to treat because of their multiplicity, difficulty in obtaining complete resection, and their predisposition for recurrence.

Case 92 Diagnosis: Osteopetrosis

Osteopetrosis is a disease related to malfunction of osteoclasts leading to decreased bone resorption and a subsequent marked degree of sclerosis of the bone and encroachment of bone upon the marrow cavity. Different forms and degrees based on inheritance of the disease are present from more severe presenting early in life to less severe presenting in adult life. Although the bone becomes markedly sclerotic it is also extremely brittle, making it predisposed to transverse fractures as seen in this case. In addition, the overall lack of bone turnover makes fractures in these patients frequently delayed in healing.

Unfortunately, multiple other complications can arise in these patients as seen in this case. The marked thickening of the cortical bone can efface the marrow leading to a decrease of all marrow elements with potential of anemia and infection as seen in this case necessitating removal of the right sided fixation hardware. In addition, the dense nature of the bone can make surgical procedures extremely difficult and because there can be marked heating of the instruments during the procedure from trying to penetrate the dense bone, there can be significant adjacent soft tissue and bony damage.

Case 91 Diagnosis: Complete suprapatellar plica

There are multiple plicae of the knee that represent the remnants of embryologic structures that resorb to a great degree in most individuals. At times these plicae may become enlarged or thickened and become symptomatic. A suprapatellar plica is frequently seen on MR exams but infrequently is symptomatic. When it is symptomatic it may be related to a lack of any perforation or resorption as seen in this patient. In this case the advanced arthritis led to marked thickening of the capsule with an increased joint effusion. The difference in signal of the effusion likely relates to hemorrhagic debris layering in the joint. The imperforate nature of the suprapatellar plica made it such that there was a marked enlargement of the suprapatellar pouch. This long standing process then subsequently yielded the indolent remodeling of the anterior femur.

In this example, aspiration of the knee yielded bloody fluid related to a likely hyperemic and friable synovium. The bloody fluid and enlargement of the suprapatellar pouch can be alarming and question a potential neoplasm but indeed are merely a manifestation of this uncommon etiology.

Case 90 Diagnosis: Turf toe

Turf toe represents a constellation of pathology involving the plantar capsuloligamentous complex of the first MTP. The injury is sustained when the forefoot is fixed to the ground with the first MTP extended and then an axial load is applied to the heel. This results in hyperextension at the first MTP with disruption of the plantar capsuloligamentous complex. As compared to the remainder of the lesser MTP’s, stability at the first MTP is imparted not as much by the plantar plate but by multiple ligaments including the metatarsal sesamoid, sesamoid phalangeal, intersesamoid, and collateral ligaments.

Within this constellation of injuries is additionally included sesamoid fractures, cartilage shearing injuries, and muscle/tendon injuries of the abductor and adductor hallucis as well as the flexor hallucis brevis and longus tendons about the first MTP. In this example, the lateral sesamoid fracture is actually a more remote injury with the medial sided injury being more acute. These injuries are often seen in football or rugby where players are landed on while already on the ground and the forefoot is fixed to the ground. Most injuries are treated non-operatively but higher grade injuries in high level athletes that fail conservative management may necessitate surgical intervention.

Case 89 Diagnosis: Hemophilia

In this case, Hemophilia A, or a bleeding disorder where clotting factor VIII is absent. Other similar bleeding disorders related to absent clotting factors can present in a similar fashion. Typically, hemophilia involves the hinge joints such as elbow, ankle, and knee, as seen in this case. Bleeding into the joints causes synovial hyperplasia and inflammatory change that destroys cartilage. Bleeding precipitating cystic change may also occur directly in the bone or soft tissue yielding a so called hemophilic pseudotumor. On imaging, the effusions with erosions are seen on all modalities. MRI helps to further show the synovial thickening with the low signal related to blood break down products (hemosideren) within the synovium. The susceptibility from the hemosiderin yields the blooming phenomenon seen on gradient echo sequences.

Unfortunately, this patient has developed an inhibitor or antibody to clotting factors used to help slow down the progression of disease. That accounts for the continued and rapid progression of the disease in this case.

Case 88 Diagnosis: Polyethylene separation

In the setting of a total knee arthroplasty or a unicompartmental arthroplasty, the polyethylene component is engaged with the tibial component be it in a mobile bearing or fixed bearing construct. There are multiple types of knee prosthesis and at times there can be confusion about an unseating or separation of the polyethylene if a minimal amount of high signal is seen interposed between the low signal polyethlene and the low signal tibial tray. However, a band of high signal fluid should never exist between the two low signal components and indicates a failure of engagement of the polyethylene component or separation of the polyethylene from the tibial tray.

Case 87 Diagnosis: Thigh splints/adductor insertion avulsion syndrome

Thigh splints is a correlative phenomenon to the much more common shin splints. Both represent an overuse type stress process with particularly insertional stress. In thigh splints this relates to the insertion of the adductor longus and brevis along the medial aspect of the proximal to mid shaft of the femur. This is seen typically in runners or high level athletes with sports involving a significant amount of running.

As with other overuse injuries these are brought on by activity and relieved by rest. These may go on to frank fractures as in other stress reactions. Using the paradigm established for medial tibial stress syndrome, a similar evaluation can be employed here. The progression of injury typically goes from periosteal edema, marrow edema/endosteal edema, hyperintense cortex, and then fracture. The greater the degree of injury typically portends a longer degree of rest for healing.

Case 86 Diagnosis: Dural Arteriovenous Fistula

Dural AVF is the most common type of spinal vascular malformation but still a relatively rare process. It is typically seen in middle aged to older men who present with progressive and insidious lower extremity weakness as well as possible back pain and bowel/bladder dysfunction. It represents a true arteriovenous fistula with dilated and tortuous veins seen on the cord surface. The abnormality can present anywhere along the neural axis but frequently presents with high signal and enlargement of the spinal cord.

Although the AVF is not necessarily adjacent to the inferior aspect of the cord or conus, this area most commonly will show cord abnormalities. The abnormal signal and enhancement of the cord is thought to be related to venous hypertension and altered flow dynamics leading to congestive edema of the cord. These are typically treated with angiography to localize the arterial supply that most often comes from a dural branch of a radicular vessel and then subsequent occlusion by use of permanent embolic agents.

Case 85 Diagnosis: Ancient schwannoma

Typically found in the older patient population this represents a degeneration of a schwannoma or neurilemmoma. This produces the findings seen here of cystic necrosis and areas of calcification. This is not a malignant degeneration which is rare in the isolated peripheral nerve sheath tumor. Like many schwannomas this mass is hyper-intense on T2 images but with internal areas of lower signal and a more fascicular appearance. The enhancement pattern is more variable than in the routine schwannoma where it is often vivid and diffuse or at the periphery of the lesion. Although cystic changes and calcification can be seen in a malignant peripheral nerve sheath tumor, those are often found in the setting of NF 1 or are much larger masses, extremely heterogeneous and have a surrounding edema pattern. The presence of the entering and exiting nerve helps in establishing a diagnosis of peripheral nerve sheath tumor versus otherwise a nonspecific soft tissue mass.

Case 84 Diagnosis: Complete disruption of one tendon in the setting of a bifurcated/bifid distal biceps tendon

Disruption of the distal biceps tendon is much less common than at the proximal attachment and tends to occur in middle aged men, typically older than 40. The short and long heads of the biceps yield tendons at approximately 7cm proximal to the radial tuberosity attachment site. There is a vast variation in the degree of intertwining or decussation between the two tendons. As in this case, at times there is a persistent bifurcated or bifid architecture of the tendons with two separate tendons extending to the radial tuberosity.

When two tendons are present, the short head of the biceps is the more medial of the tendons and has a more distal insertion on the radial tuberosity. The long head of the biceps is the more lateral tendon and inserts more proximally. In the setting of a selective disruption of one of the tendons, by in large it is the short head but in this example it is the more lateral tendon or long head tendon that is disrupted. However, there has been a strain of the short head seen best on the axial IR images and hence this is not completely, an isolated or selective injury. The importance of these findings is to be aware that injury can have still been sustained even if a tendon attachment is present at the radial tuberosity and surgery may still be necessary for the selective disruption.

Case 83 Diagnosis: Non-ossifying fibroma with cystic change and pathological fracture

Radiographs demonstrate a lucent lesion of the distal tibia that is eccentrically located and associated with prominent periosteal reaction. The MRI demonstrates a complex mass with a marked amount of edema in the soft tissue and periosteal reaction. The mass has both cystic components and enhancing solid components. It is associated with a mark thinning of the cortex but without penetration through the cortex or an associated soft tissue mass.

Diagnosis: Non-ossifying fibroma with cystic change and pathological fracture
Non-ossifying fibroma (NOF) is a common benign entity of the bone that frequently is of no consequence. They may at times be associated with cystic change or secondary aneurysmal bone cysts. Additionally, the lesions, if large enough (typically involving greater than 50% of the transverse diameter of the bone) may be associated with a stress fracture. In this case, the patient’s trauma led to a stress fracture through the area of the enlarged and cystic NOF yielding the periostitis and edema as shown.

The MRI clearly demonstrates an enhancing, solid component and an additional muticystic component containing fluid levels. This latter portion is in keeping with the imaging findings of a secondary aneurysmal bone cyst (ABC) component in the setting of NOF. Although not as frequent as a secondary ABC in the setting of giant cell tumor, telangiectaic osteosarcoma, osteoblastoma, chondroblastoma, or others, NOF is a well documented lesion associated with ABC. In this case, given the associated fracture and slightly aggressive appearance of the findings, a curettage and packing was performed.

Case 82 Diagnosis: Zone II flexor injury

The flexor tendons of the hand are of the utmost importance for finger functioning. There is a vast amount of information that relates to these injuries which goes beyond the scope of this presentation. The injuries are typically classified by their zone of injury with this injury involving the FDP and FDS between the palmar crease and FDS insertion. The importance of imaging is to show the surgeon a road map for potential repair in the more acute setting and particularly for the degree of tendon retraction. In the more long standing setting, knowing the degree of tendon gap can help with preoperative planning for reconstruction of the tendon via a graft.

Additionally, information as relates to the annular pulleys is of benefit to assess for need of reconstruction to allow appropriate flexor tendon function and prevent bowstringing of the tendon. As the FDP, provides flexion at the DIP, that corresponds to the lack of flexion this patient has at the DIP. Although there is a split of the FDS, the limbs remained intact to their attachment allowing flexion at the PIP. Given the timing of this injury, 3 months, and the tendon gap a reconstruction will likely be required.

Case 81 Diagnosis: Synovial osteochondromatosis

A synovial metaplasia typically occurring in middle aged adults yielding innumerable areas of proliferated synovium and a large joint effusion with a mono-articular distribution. With time, focal areas calcify and ossify and may develop large areas of conglomerate ossification. Typically, there is relative preservation of the joint cartilage, but there may be indolent erosions particularly in less capacious joints such as the hip or elbow.

The differential diagnosis includes a “secondary” osteochondromatosis which represents multiple ossific and calcified bodies in the joint related to degenerative change. PVNS will not calcify or ossify and the synovium does not yield the rice body configuration. Classically, TB yields rice bodies but would not give small calcifications and would yield marginal erosions as well as juxta-articular osteoporosis. Rheumatoid arthritis in addition, can give a rice body configuration to the synovium but would yield erosions at the bare areas, a loss of joint cartilage and joint space, and typically involves multiple joints.

Case 80 Diagnosis: Ceramic liner fracture

A rare complication of a ceramic on ceramic total hip arthroplasty related to the brittle architecture of the ceramic components. Improvements have been made in the components but this complication does still present. It classically presents with a squeaking with ambulation but does not have to. This often signifies a non-displaced crack that can go on to a catastrophic fragmentation of the prosthesis. This complication necessitates revision as was done in this example.

This case highlights a couple of other points. It is important to understand the limitations of any given radiology exam and frequently, no individual exam can answer every question. MRI, particularly with recent advances in artifact reduction, is an exquisite tool at diagnosing complications in THA but even that can not answer all questions. In this case the ceramic on ceramic articulation is better seen with a CT exam. However, both the technique at acquiring the exam and then reading the exam must be tailored in such a way to allow optimal visualization of the hardware. Also, comparison to older exams is helpful to help prevent erroneous diagnoses. In this case, a degenerative, subchondral cyst could be mistaken for a focus of osteolysis which may confound the clinical picture.

Case 79 Diagnosis: Fibrolipomatous hamartoma with macrodystrophia lipomatosa

Fibrolipomatous hamartoma (aka lipofibromatous hamartoma, neural fibrolipoma) is a benign neoplasm of the nerve with disorganized overgrowth of nerve elements encased in a fibro-fatty mass. This most commonly is seen in the median nerve but can be seen in the radial, ulnar, or as in this case the plantar nerves. It yields a pathognomonic appearance with a “coaxial cable” appearance on axial images and a "spaghetti" appearance on coronal or sagittal images. This relates to the overgrowth of neural and surrounding fibrofatty elements.

Macrodystrophia lipomatosa (ML) is a focal form of gigantism that can be seen from numerous causes but is often seen in the setting of fibrolipomatous hamartoma. ML results from an overgrowth of all mesenchymal elements but especially fatty, soft tissue. In addition, there is overgrowth of bone and neural tissue. This process can be seen of the entire hand or foot or of only select rays (typically the second or third). The process ceases with skeletal maturity.

Case 78 Diagnosis: Hardware failure and displacement

In this case there has been a failure of incorporation of the intervertebral graft with no bony bridging across the disc space and posterior displacement yielding mass effect upon the traversing right sided nerve root. Related to the prior posterior decompression and lack of graft fixation there has been increased load transmitted to the L4-L5 segment causing a breakdown with marked irregularity of the endplates. The marked edema at L4-L5 and irregularity of the endplates would question infection. However, the preservation of a large area of the endplates and no associated paravertebral collection argues against infection.

In this instance serological markers were obtained and were not suspicious of infection, nor was there an overall clinical suspicion. The inability to see the carbon fiber cage on the x-rays is because they are radiolucent but can be seen on MRI and CT. Our surgeons use cages with metallic beads so that the cages can be identified on x-ray and their position can be evaluated on x-ray. In this case, revision surgery was performed with removal of the posterior displaced cage and with anterior and posterior fusion performed from L2-S1 with additional iliac fixation.

Case 77 Diagnosis: Fracture of the polyethylene tray

Total knee arthroplasty has a variety of known complications inclusive of infection, periprosthetic fracture, and osteolysis/loosening. Wear of the polyethylene tray yields particles inducing osteolysis which is not infrequently seen but an actual fracturing of the poly tray is rare. As in this case the defect can lead to abnormal mechanics that are perceived as instability as the metal condyle falls in and out of the defect. Perhaps in this case the findings are so much more conspicuous on the CT arthrogram as compared to the MRI because there has been interval displacement of the fragments. Had the displaced fragments been present at the time of the MRI they would be able to be perceived particularly given the recent, enhanced techniques. This patient is scheduled for revision surgery.

Case 76 Diagnosis: Morel-Lavallée lesion

Morel-Lavallee(ML) injury is an internal degloving of the fascia from the adjacent subcutaneous fat. Technically referring to a shearing injury around the greater trochanter, the injury is most typically seen at areas of prominent subcutaneous fat with the greater trochanteric area being most common. Other locations are around the knee and lumbar spine. The injury can have multiple appearances on MR imaging based on the degree of seroma that has formed or a greater degree of hemorrhage and organizing hematoma.

The injury can be problematic as it may lead to necrosis of the adjacent tissue as well as infection. In the acute setting debridement is often performed. If the lesion is only recognized after it has become encapsulated, a percutaneous drainage can be attempted but is frequently unsuccessful necessitating multiple attempts or surgical removal.

Case 75 Diagnosis: Re-tear of the rotator cuff

There have been many different ways in which the rotator cuff has been repaired. Recently, a double row technique with suture fixation devices has gained popularity. Bio-absorbable devices have become popular and these are said to become resorbed and have subsequent bone formation. In some individuals as in this case, there is a more prominent inflammatory response that is engendered and may cause a subsequent loosening of the fixation hardware. As relates to the determination of a re-tear, careful scrutiny is warranted. All repaired tendons have irregular or increased signal but what is important is whether or not the tendon is completely disrupted or ruptured and is there a tendon gap. Frequently, very small defects persist in a tendon without re-tear as a water tight seal may be difficult to achieve at the time of surgery. As relates to the tendon gap, this may have fluid signal intensity, but often as in this case, there is intermediate inflammatory or granulation tissue filling the gap and not simple fluid.

Case 74 Diagnosis: Bucket handle tear lateral meniscus

A bucket handle tear is a type of longitudinal tear of the meniscus that is typically seen in the younger, active patient population particularly sustained during twisting activities. Longitudinal here implies along the long axis of the meniscus with the meniscal tissue then displaced so that it resembles the handle of a bucket. Knowing the architecture of the meniscus is paramount as in this case. The anterior and posterior horns of the lateral meniscus are typically about the same size and hence all of the tissue anterior can not be a normal lateral meniscus. In addition, through the intercondylar notch there should only be two structures, the ACL and PCL. Any other structure present in the notch must be questioned for displaced tissue.

During the cutting motion precipitating this injury, many other injuries occurred mostly related to a valgus stress and external rotation but additionally with a lower grade injury related to varus stress. These included a complete ACL tear with impaction fractures, peripheral tear posterior horn medial meniscus with associated impaction injury, proximal injury of the superficial MCL, and a partial disruption of the popliteofibular ligament with the remainder of the posterolateral corner structures being intact.

Case 73 Diagnosis: Extensor mechanism central slip disruption

The extensor mechanism of the finger is a highly complex and intricate system. At the level of the metacarpal phalangeal joint, the extensor tendon is stabilized by the sagittal bands. Distal to this, contributions of the intrinsic and extrinsic musculature help form the central and lateral slips. The central slip inserts into the base of the middle phalanx and if injured and left untreated produces a flexion deformity at the PIP.

The lateral slips then extend distally to subsequently form the conjoint tendons which insert into the distal phalanx. With disruption of the central slip, the lateral slips over time rotate to a more volar position yielding increase force at the distal insertion site and an extension at the DIP. This together with the PIP flexion yields a Boutonniere deformity. In an acute setting, splinting may be tried but in the chronic symptomatic patient or when there is a block to anatomic reduction in the acute setting, surgery is required.

Case 72 Diagnosis: Pseudoaneurysm following total knee arthroplasty with recurrent hemarthrosis

Recurrent hemarthrosis following total knee arthroplasty is occasionally is related to pseudoaneurysm (psA) formation as in this case which then can bleed and cause a hyperemia of adjacent, friable synovium. The psA can be seen in this case as the early filling mass on the angiographic study and by the mass showing bidirectional flow on the Doppler ultrasound.

This bidirectional flow is often described as a yin-yang appearance and is characteristic. Within the psA there is arterial flow which at the neck may become particularly turbulent. The early staining synovium relates to a local hyperemia and proliferation of the synovium. Most cases of recurrent hemarthrosis following TKA are less well understood and do not have an associated psA. They are postulated to be secondary to bleeding that causes hyperemic, friable synovium to proliferate and subsequently bleed, leading to a vicious cycle. The PD images of this study show the intermediate hemorrhagic debris as well as the high T2 weighted signal mass which represents the psA. As in this case, psA can be treated with transcatheter embolization typically yielding resolution of the problem. In the setting of recurrent hemarthrosis without psA and with a dense staining synovium, transcatheter embolization can be attempted if a dominant vessel is found. Arthroscopic synovectomy may be attempted if there is staining of the synovium without a dominant vessel.

Case 71 Diagnosis: Rapidly destructive osteoarthritis/subchondral fracture

A still confusing entity to many, these subchondral fractures were in the past thought to be a primary necrosis. Pathology specimens demonstrated areas of necrosis which would be seen in the setting of any fracture and more so represent secondary necrosis than the primary process. This process is typically in the older, osteoporotic population without a remembered traumatic event. The initial fracture likely continues to propagate as the patient continues to bear weight.

The entity at times may be difficult to discern from an infectious process although even a septic joint does not tend to produce this degree of destruction in such a rapid time course. Other clues are the “clean” truncation of the femoral neck and well maintained subchondral surface of the acetabulum. In the setting of infection, these surfaces are frequently very irregular. An aspiration at times may be warranted and patients are treated with joint replacement.

Case 70 Diagnosis: Posterior shoulder dislocation

Posterior shoulder dislocations are much less frequent than anterior dislocations and are as a result of axial loading to an adducted and internally rotated shoulder. In an acute setting, the humeral head may be persistently internally rotated and posteriorly positioned, if the head does not reduce. Once reduction is achieved typical findings are as shown in this case. These findings include an impaction fracture of the anteromedial humerus referred to as a reverse Hill Sachs or McGlaughlin lesion.

Posterior labral and glenoid injuries are analogous to their anterior counterpart as relates to the myriad of soft tissue Bankart injuries or an osseous Bankart injury. Although not present in this case there may be a concealed chondral injury or Kim’s lesion. Evaluation of the capsule is paramount particularly with concern of the posterior band of the IGHL and a humeral detachment which frequently necessitates an open stabilization. As shown in this case, a posterior translation can yield injury about the rotator interval. This is also critical to evaluate as this area may also require stabilization at the time of surgery to achieve a satisfactory outcome.

Case 69 Diagnosis: Adhesive arachnoiditis/arachnoiditis ossificans

Adhesive arachnoiditis is an inflammation of the meninges leading to inflammation and scarring of the nerve roots within the subarachnoid space. This frequently progresses in stages with a thickening and clumping of the nerve roots, followed by scar adherence to the periphery of the thecal sac, and then subsequent marked scarring of the thecal sac yielding an irregular sac with adhesions leading to a compartmentalization of the thecal sac. Very rarely, as in this case, there can then be subsequent ossification at the areas of scarring and adhesions leading to arachnoiditis ossificans.

The process can be extremely debilitating and painful with patients typically having back pain as well as radicular or non-radicular type lower extremity pain. The cause is still not yet determined although the pathology is now seen most commonly in the post operative setting. Limited treatment successes have been found with intrathecal injection, spinal cord stimulation, or lysis of adhesions.

Case 68 Diagnosis: 5th Metacarpal fracture dislocation/reverse Bennett fracture

This injury can be difficult to diagnose on radiographs and frequently can only be identified by the overlap of the bones at the joint on frontal or oblique views. The remainder of the digits limit ability to see the dislocation on the lateral view. By in large these injuries occur in men and are either from sports, MVA, or trauma/fights and typically are related to an axial load imparted to the wrist.

The proximal migration and dorsal dislocation of the metacarpal is related to a pull from the extensor carpi ulnaris as its insertion is at the base of the 5th MC. As in this case, the injuries typically are unstable and require surgical intervention with fixation.

Case 67 Diagnosis: Pedunculated paralabral cyst emanating from inferior labrum/transverse acetabular ligament

Paralabral and parameniscal cysts are common processes of the shoulder and knee respectively and paralabral cysts are becoming increasingly better recognized in the hip. These can present as large fluid masses that need to be delineated from the multiple bursae that can occur around the hip. Paralabral cysts, as in the shoulder, emanate from tearing or previous injury of the labrum as is seen in this case. The cysts themselves may cause pain from mass effect or by affecting adjacent neural structures as seen in this case. The edema of the addutor brevis in this case may be from direct mass effect of the cyst or from mass effect upon the branches of the obturator nerve. Symptomatic treatment can be rendered by ultrasound guided aspiration and steroid injection but often hip arthroscopy is required to address the underlying labral pathology.

Case 66 Diagnosis: Postpartum Pelvic Instability

The key piece of history withheld is that the patient had given birth 18 months ago with then persistent anterior and posterior pelvic pain. Chronic postpartum pelvic pain is an uncommon but potentially debilitating condition whose incidence and etiology are without a clear understanding. By in large most women respond well to conservative measures such as physical therapy and anti-inflammatory medication. When persisting and recalcitrant to conservative measures, surgical intervention may be warranted. Depending on the site of the patient’s pain anterior or anterior/posterior fusion and/or fixation may be performed.

Case 65 Diagnosis: Idiopathic Spinal Cord Herniation

A rare but potentially, severely debilitating pathology thought to be related to a dural defect which allows a free flow of CSF so that it enlarges the defect. This then allows a ventral displacement of the CSF as well as an enlargement of the dorsal subarachnoid space. The defect also yields turbulent flow that is manifest by the areas of lower signal within the CSF on the T2 and IR pulse sequences. The lesion typically occurs from T4 to T7 and is often associated with atrophy of the spinal cord and an anterior kinking which are seen in this example. Within the differential diagnosis is an intradural arachnoid cyst which can appear similar but will not contain the areas of turbulence. Additionally, if myelography is performed, there will be free flow of contrast through the area in the setting of cord herniation but not in the setting of an arachnoid cyst. Idiopathic cord herniation frequently warrants surgery depending on the symptoms. This patient is currently being further evaluated.

Case 64 Diagnosis: Infectious Discitis/Osteomyelitis

Following surgery many complications are possible including infection, fracture, and when orthopedic hardware is placed- mechanical loosening. Often, multiple imaging modalities and even biopsy are necessitated to emerge at a diagnosis. In this case, on the CT exam, there is lucency around the hardware with portions of the endplates showing a loss of cortical margins. It is difficult to know from that study alone whether or not the findings are from mechanical loosening and aseptic bone resorption or infection.

The clinical history in this case is also nonspecific and so further investigation with MRI was pursued. The degree of abnormal signal of the disc and bone together with the inflammatory changes in the soft tissue are in keeping with infection. A fracture may have similar findings but no fracture line was seen and the degree of enhancement would be atypical. Degenerative changes likewise may present similarly but the extent of the findings and degree of enhancement would again be atypical.

Infection in this situation is typically from hematogenous spread that may be from a genitourinary, dental, respiratory, or other origin. In the adult, the spread is first to the endplates with then subsequent spread into the disc and then extending into the adjacent end plate. As in this case, patients are treated with antibiotics and in this case additional decompression and fusion was performed. The decompression was secondary to the central canal stenosis and the fusion because of the degree of bone resorption yielding an unstable fusion construct.

Case 63 Diagnosis: Complications of shoulder arthroplasty with multiple periprosthetic fractures

This case demonstrates only a couple of the complications that can come in the setting of joint arthroplasty and especially in this case shoulder arthroplasty. Hemiarthroplasties are known to be at risk for progression of instability often related to progressed degeneration and tearing of the rotator cuff as seen in this case. In addition, patients often suffer from propagation of arthritis necessitating total shoulder arthroplasty as seen in this case. One other complication related to progressive disease of the cuff is a loss of the acromiohumeral interval yielding increased stress on the coracoacromial arch and precipitating fractures as in this case of the coracoid.

Total shoulder arthroplasties and in particular in this case, reverse total shoulder arthroplasties, can have complications. Scapular notching, difficulty in seating the base plate, dissociation, infection, and loosening are well known complications. In addition, particularly in the setting of the reverse TSA, acromial and scapular spine fractures are becoming more recognized. These fractures may of course be painful but may necessitate additional fixation as well.

Case 62 Diagnosis: Costal Cartilage Fracture

A rare and not well known traumatic injury that can be seen in contact athletes especially in rugby players or other athletes that sustain direct blows to the chest wall and are without substantial padding.  The prevalence of this injury as well as the capability for healing of the cartilage are not well known.  By in large, athletes can return to sport with symptomatic relief but problems such as chest wall instability and subsequent respiratory issues may be more problematic.

Case 61 Diagnosis: Displaced radial head/cartilage anlage fracture

The elbow has a known time course for the appearance of its multiple epiphyses and apophyses (secondary growth centers). For the purposes of this case, the capitellum is followed by the radial head and then the medial epicondyle with the capitellum beginning to ossify at 1, radial head at 4, and then the medial epicondyle at 7. The cross sectional imaging shows clearly the fractured/displaced unossified radial head epiphysis as soft tissue attenuation on the CT and intermediate signal intensity on the MRI. It contains small areas of early ossification of the secondary growth center on both imaging modalities. Particularly on the coronal PD and MPGR sequences, the cartilage anlages all demonstrate intermediate signal.

In this case the patient was a six year old boy who had sustained trauma several months prior and was seen at an outside institution and seen only recently at our institution. However, without a knowledge of prior trauma the periosteal reaction with a soft tissue component and ossification could be seen in the setting of a neoplasm. Periosteal reaction also may be seen in the setting of infection as may a soft tissue mass representing an abscess or phlegmon. This demonstrates the imperative nature of obtaining a good history particularly as relates to the interpretation of images.

Case 60 Diagnosis: Pathological fracture of a unicameral bone cyst

A unicameral bone cyst (UBC) is a lesion of bone with a single fluid filled chamber that is lined by a fibrous membrane. The lesions occur in children and young adults and tend to occur at the metaphyses, often adjacent to the growth plate. Although a single chamber, on MRI exam, small internal septations may be seen, frequently following previous trauma. However, multiple, fluid/fluid filled chambers are not present as would be seen in an aneurysmal bone cyst.

UBC's may cause an erosion of the adjacent cortex but do not typically yield an expansion of the bone. As in this case, they may be complicated by fracture that cause bleeding into the cyst yielding fluid/fluid levels as well as in this case a bone fragment or so called fallen fragment sign. The lesions may regress spontaneously or may require intervention via orthopedic surgeons with curettage and packing or other procedures to produce healing.

Case 59 Diagnosis: Elastofibroma Dorsi

Elastofibroma Dorsi is a benign soft tissue tumor which is typically seen in the older patient population and is more common in women than men. It is classically found, as in this case, at the tip of the scapula or infrascapular and is interposed between the scapula and the chest wall. It is often found deep to the serratus anterior or latissimus dorsi muscle. The mass is thought by many to be perhaps in part related to mechanical irritation.

Given that the mass is composed of streaks of fibrous tissue interspersed with fatty elements, it yields intermediate to low signal on most pulse sequences but with other foci of fat signal as is seen in this case. It lacks an overlying capsule accounting for its ill defined or somewhat infiltrative pattern. The mass is benign and if seen in a typical location needs no further follow up. Approximately half of the time patients state associated pain, snapping, or clicking that may precipitate excision with recurrence being particularly rare.

Case 58 Diagnosis: Glomus Tumor

A glomus tumor is a hamartoma (tissue normally found at a location but growing in a disorganized pattern) of the neuromyoarterial (nm) apparatus. Typically found in women from 30 to 50 years of age, although small, the masses are intermittently, extremely painful. Patients have often 2-3 years of symptoms before seeking treatment. They are as in this case, high in signal and often yield erosion of the underlying bone. Given the classic appearance in this case, no contrast was administered, but as the mass represents proliferation of the nm apparatus, it will avidly enhance. They typically occur at the subungual location as in this case but occasionally extend into the underlying bone.

Case 57 Diagnosis: Polyostotic fibrous dysplasia with pathological fracture

Fibrous dysplasia is a noninherited abnormality of the bone forming mesenchyme where osteoblasts do not mature normally and normal bone is replaced by immature, woven bone and fibrous tissue.  This accounts for the areas of abnormal density of the bone inclusive of the ground glass, trabecular type architecture, and sclerosis. Although the ground glass architecture is classic, there can be an array of abnormal appearance of the bone as in this case. This abnormal bone is structurally weak allowing for expansion, remodeling, and pathologic fracture as in this case.

Other complications such as malignant degeneration are exceedingly rare with precocious puberty (McCune Albright syndrome) and intramuscular myxoma (Mazabraud syndrome) being more common albeit still rare associations. Even when a discrete fracture is not present, the patient may have skeletal pain thought to be related to bony remodeling or underlying endocrine abnormalities.  As seen in this case, multiple fractures may occur requiring multiple sites of fixation.

Case 56 Diagnosis: Septic arthritis/osteomyelitis

Infection is a devastating process which can lead to a rapid obliteration of articular cartilage or in the postoperative setting can lead to significant morbidity and mortality.  In our practice, we have found a relative sensitive and specific sign of septic arthritis manifest by an aggressive or lamellated synovitis as demonstrated in this case.  Additional findings of a large joint effusion, edema in the adjacent subchondral bone, and edema extending into the adjacent soft tissues effacing normal soft tissue planes assist in the diagnosis. On radiographs, the infectious process often manifests as osteopenia related to a marked degree of hyperemia. The precipitous cartilage loss leads to the marked degree of joint space loss.

Osteomyelitis may accompany or occur separately from a septic joint. On MR examination, the presence of edema alone in the bone may relate to infection or a reactive process. However, the presence of bony destruction indicates osteomyelitis. The presence or absence of soft tissue or osseous fluid collections (abscesses) is of great concern given their relative inability to be treated with antibiotics alone and frequently necessitating surgical debridement.

Case 55 Diagnosis: Paralabral ganglion cyst

Degeneration and tears of the glenoid and acetabular labrum may yield paralabral ganglion cysts.  If the tear itself is not clearly delineated on imaging, it is presumed to be present. As in this case, the cysts can extend into spaces where neurovascular bundles are present and cause mass effect upon the neurovascular bundles. More commonly, tears of the superior or posterior glenoid labrum yield ganglion extending into the suprascapular notch or spinoglenoid notch. Extension into the quadrilateral space is less common and places the traversing axillary nerve at risk.

Compromise of the nerve affects the innervated musculature and yields neurogenic edema and in a more long standing process can cause  fatty atrophy of the musculature.  As in this case, not all the musculature innervated has to be affected. The deltoid musculature in this case was normal. Treatment may entail ultrasound guided aspiration to help resolve the impingement of the nerve. If unsuccessful in mitigating symptoms, surgery is required to asses the underlying pathology, the labral tear.

Case 54 Diagnosis: Vascular Malformation

The generic term of vascular malformation is given as the diagnosis as there is still debate about how to appropriately term these lesions. The term hemangioma is often used to describe a capillary or smaller vessel lesion that is seen of the superficial soft tissue in very young children and typically involutes by 4 to 5 years of age. The lesion shown here is described by some as a cavernous type hemangioma and by others as a venous malformation. In either way, it represents larger, dilated blood channels with slow flowing blood. These are often somewhat more deep seated and may become painful with activity. These lesions as in this case, often will show a high signal, tubular architecture corresponding to the slow flowing blood in the dilated vascular channels. The calcifications or phleboliths at times will show a characteristic, lamellated pattern as in this case with a central lucency. These masses are often well demarcated but at times will be somewhat more poorly marginated. Areas of fat may be seen interspersed within these masses. If painful these masses may be resected or as in this case their mass effect may necessitate resection. Although, not malignant, recurrence rates can be seen in up to 25% depending on the margins at excision.

Case 53 Diagnosis: Transverse Process Stress Fracture

Cases have been presented previously of stress fracture but this case highlights an unusual fracture found infrequently with frequent flexion/extension and rotation activities. It also shows the often subtle nature of findings on radiographs and their difficult interpretation. In this case, the periosteal bone relates to early fracture healing and the central, oval lucency likely represents bone resorption at the site of the fracture. Although the oval lucency may on the surface appear to represent an osteoid osteoma, it does not have the classic well demarcated circular appearance nor any ossified central portion to suggest a nidus. In addition, the history is much more suggestive of an overuse injury than osteoid osteoma. This case highlights an important differential diagnosis particularly in the pediatric population where there is focal peiosteal bone/cortical thickening. As in this case a stress fracture and osteoid osteoma should be considered. In addition, infection, particularly a more chronic infection and eosinophilic granuloma should be considered. The architecture of the findings but also the history are important in reaching the correct diagnosis. As shown in this case, the complimentary nature of multiple studies can also not be stressed enough in reaching the correct diagnosis.

Case 52 Diagnosis: ACL Disruption with Segond fracture and partial MCL tear

The most typical mechanism of ACL disruption is a pivot shift injury where a valgus stress is placed on a flexed knee with the femur internally rotated. This yields a classic edema pattern of the posterior lateral tibial plateau and the sulcus terminalis of the lateral condyle. The sulcus of the lateral condyle when deeper than 1.5 mm indicates an ACL tear and can at times be identified on radiographs. A Segond fracture is an avulsion injury of the lateral joint capsule. The mechanism of injury relates to internal rotation of the tibia with a varus moment imparted to the knee. It has a high association (75-100%) with ACL injuries as well as of the menisci. Given that in this case there was additionally, an MCL injury, one can see the often complex mechanisms yielding injury patterns of the knee.

Case 51 Diagnosis: ALPSA

ALPSA or anterior labral periosteal sleeve avulsion is a Bankart variant or variant of an anteroinferior labral tear frequently seen in the setting of an anterior translational event (subluxation or dislocation). The ALPSA has a stripped but intact scapular periosteum allowing medial displacement of the labrum, which is important for the surgeon to be aware of preoperatively. Specific mention was made of the intact IGHL to make clear the absence of a HAGL lesion (humeral avulsion of the glenohumeral ligament). This lesion to most necessitates the need for an open instead of arthroscopic repair. The posterolateral impaction represents a classic Hill Sachs lesion that when large may necessitate soft tissue or bony grafting. The small avulsion of the anterior glenoid represents a very small bony Bankart lesion. Again, when this lesion becomes large it may necessitate bony augmentation to help prevent recurrent subluxation/dislocation.

Case 50 Diagnosis: Calcium hydroxyapatite

Calcium hydroxyapatite (CH) can deposit in and around tendons, bursae, or less commonly about a joint. This deposition may be referred to as calcium hydroxyapatite deposition disease but more commonly as calcific tendinosis or calcific tendonitis. The CH can cause a marked inflammatory response as is seen in this case and may involve the soft tissues and/or bone. In the bone, this may yield erosive change and when deposited in the joint may lead to joint destruction. CH’s typical appearance on radiographs is a cloud like, amorphous density lacking architecture (no cortical/medullary differentiation). On MRI, it shows low signal intensity on all pulse sequences, and when painful, typically is associated with a marked amount of surrounding edema/inflammatory change.

Case 49 Diagnosis: Lipoma Arborescens

Lipoma arborescens is a benign, intra-articular process that results in fatty deposition in the synovium. It is most typically seen in the setting of a long standing arthrosis. Classically associated with rheumatoid arthritis and inflammatory arthropathies, it can be seen as in this case, in the setting of bland, degenerative osteoarthritis. Intra-articular masses are exceedingly rare and this entity should not be confused with a synovial hemangioma, synovial chondroma, or synovial chondrosarcoma. In addition, when viewing studies, frequently, fat insinuates about a knee joint effusion but is not intra-articular. This can be particularly confusing when viewing only one plane but is frequently confirmed when evaluating all planes of imaging.

Case 48 Diagnosis: Infantile or Congenital Coxa Vara(CCV)

Infantile or congenital coxa vara results from abnormal maturation of the proximal femoral physis that causes decreased ossification, weakening of the bone, and subsequent coxa vara.  Classically, as in this case, there is a Y shaped configuration of the proximal femoral physis and a focus of ossification inferomedially. Patients typically present from the time they start walking up to about 6 years of age and present with a limp.

There is often a mild limb length discrepancy of 2-4 cm as is seen in this case.  If necessary, a valgus osteotomy is performed.  Osteotomy is indicated for a Hillgenreiner epiphyseal angle (HEA) of > 60 degrees or an HEA of 45-60 degrees with increasing coxa vara.  In distinction, to proximal femoral focal dysplasia (PFFD), the varus deformity in CCV is at the level of the physis and not subtrochanteric as in PFFD. Also, in PFFD, there is typically a more pronounced limb length discrepancy.

Case 47 Diagnosis: Sprengel's Deformity

Sprengel’s deformity is a congenital deformity yielding an elevation and medial rotation of the scapula related to a failure of the normal caudal migration of the scapula. In approximately 30% of the deformities, an omovertebral bone is present that extends from the posterior elements of the cervical spine to the native scapula. This may be connected directly to the scapula by osseous bridging or by non-osseous (cartilage or fibrous tissue) bridging as in this case. The deformity is most typically seen  in the setting of a Klippel Feil (KF) syndrome where there is fusion of two or more cervical vertebrae. KF often has associated other vertebral anomalies, a webbed neck, cervical ribs, and cardiac/pulmonary/renal/ and GI anomalies.

Case 46 Diagnosis: Sportsman's Hernia.

A confusing and poorly named entity thought originally to be related to an inguinal hernia given pain in the inguinal region.  The entity has subsequently been shown to represent a disruption of the rectus adductor aponeurosis.  This entity may be seen in the setting of other causes of athletic pubalgia such as osteitis pubis, manifest by edema and cysts extending anteriorly to posteriorly about the pubic symphysis, as well as adducor muscle injuries.  A sign previously described on arthrography is employed on MRI which is the secondary cleft sign. This represents a disruption of the pubic symphysis capsule as it blends with the rectus adductor aponeurosis.

Recently described are two typical patterns of sportsman’s hernia. The one is more lateral at the rectus/adductor aponeurosis and is associated with asymmetric pubic edema, an ipsilateral secondary cleft, and injury of the rectus and adductor. The other pattern is centered more at the pubic symphysis with bilateral secondary clefts and typically with a breech of the rectus but not often extending into the adductor longus. This case represents more of the second type of process, centered at the pubic symphysis, but with a clear tear of the adductor. Therefore, there likely is a continuum or spectrum across these two typical patterns.

Case 45 Diagnosis: Posterior hip subluxation with acetabular fracture and displaced labrum.

Posterior translation events of the hip are typically associated with high speed motor vehicle accidents where the flexed knee impacts the dashboard with a flexed hip driving the femoral head posteriorly. This can yield fractures of the posterior acetabulum, femoral head, and potential injury to the sciatic nerve. Gaining increased recognition is that athletes may sustain posterior subluxations either related to a flexed knee impacting the ground with a flexed hip, blow from behind while on all four limbs, or impaction of the foot on the ground with an extended leg and locked knee transmitting force posteriorly to the hip.

As compared to a dislocation, the subluxation event results from a less amount of force imparted to the hip and has a more subtle clinical and radiographic presentation. As seen in this case, there is often a posterior wall or lip fracture of the acetabulum. Often a joint effusion or hemarthrosis is seen and injury is seen of the anterior and posterior joint capsules. Missed diagnosis and particularly with displaced tissue into the joint may predispose to further translational events and long term instability. Additional morbidity includes the risk of avascular necrosis and potential for premature degenerative joint disease.

Case 44 Diagnosis: Transient Lateral Patellar Dislocation.

Transient lateral patellar dislocation (LPD) is a well documented injury caused by internal rotation of the femur on a fixed tibia with flexion of the knee and firing of the quadriceps mechanism. This leads to a laterally imparted force on the patella. With relocation of the patella, impaction fractures are seen of the anterior aspect of the lateral femoral condyle and the medial patellar facet. Positioning of the impaction along the central to inferior aspect of the medial patella relates to the degree of flexion of the patella at the time of injury. Along the medial aspect of the knee is a documented trilaminar structure that supports the medial aspect of the knee but with the medial patellofemoral ligament being the key stabilizer along the medial aspect of the knee. The disruption of the MPFL may be at the patellar, midsubstance, or femoral attachment. Often, as in this case force is transmitted through the entire ligament yielding diffuse injury. Recently, direct MPFL reconstruction has become a more routine procedure for some of these patients. Underlying osseous architecture is a known predisposition for recurrent LPD including trochlear hypoplasia, patella alta, patella tilt, elevated quadriceps angles, and others. Treatment often relates to reconstituting normal osseous relationships to help prevent recurrent LPD and subsequent early cartilage loss. In this case, the additional OCD of the medial condyle is not a classic finding although often MCL and medial meniscal injuries are seen in the setting of LPD.

Case 43 Diagnosis: Spondyloepiphyseal Dysplasia (SED).

SED is an inherited dysplasia that involves the ends of the bones or epiphyses and the spine. It comes in two variants, congenita ( present at birth) and tarda which has a normal appearance at birth and then develops at 4 years of age and older. Given the underlying dysplasia there is premature osteoarthritis which in this patient may have been neglected. In the spine, there is typically a hypoplastic dens which leads to spinal instability and as in this patient leads to fusion to help prevent a catastrophic event. The presence of an os odontoideum or non fused tip of the dens may be seen but is not as typically present.

The vertebral bodies are decreased in height and at times may be completely flat yielding platyspondyly. Ovoid or trapezoidal bodies in the pediatric patient typically than yield vertebrae in the adult with decreased height, increased AP diameter, and end plate irregularities as seen here. Severe stenosis or C1/C2 kinking may be found as compared to the typical cervicomedullary kinking found in achondroplasia. In this patient, no myelopathic symptoms were present, astonishingly so. Imaging of the other appendicular structures would have shown multiple areas of epiphyseal dysplasia and advanced arthrosis.

Case 42 Diagnosis: Loosening of femoral component in THA.

In the setting of potential loosening of a component in joint arthroplasty, evaluation at the multiple interfaces (bone/prosthesis/cement) is of great consequence and requires close scrutiny. Frequently described evidence of loosening is greater than 2mm lucencies propagating among multiple Gruen zones (especially beyond those of the periarticular zones of 1,7,8,15). On arthography, propagation beyond the intertrochanteric line is often frequently used as an indicator of loosening. These findings do require correlation with clinical history and physical exam.

As a means to obviate the need for percutaneous intervention, MRI protocols have been developed over the last decade to accurately asses for loosening without joint injection/aspiration. The accuracy of this modality has been validated multiple times in the literature. As a way to improve this, new prototype pulse sequences, as shown here, are being fabricated to reduce susceptibility artifact at metal/tissue interfaces as to allow even better interpretation. This is particularly important in the setting of markedly ferrous components as used in metal on metal constructs that produce a tremendous amount of susceptibility artifact.

Case 41 Diagnosis: Ankle syndesmotic and deltoid ligament tears with Maissoneuve fracture.

Maissoneuve fracture is a proximal fibular fracture typically seen in the setting of an external rotation injury yielding a disruption of the syndesmotic complex, propagating into the interosseous ligament, and then extending into the fracture of the proximal fibula.  Often seen in association with a medial malleolar fracture or disruption of the deltoid ligament rendering an unstable ankle.  The deltoid ligament disruption can be identified directly on the MRI or by the widening of the medial clear space beyond 4-5mm.  As the ankle has been rendered unstable, fixation is then required.

Case 40 Diagnosis: Serous atrophy/gelatinous transformation of marrow with superimposed, post traumatic olecranon bursitis.

In the setting of anorexia or cachexia, the body will use whatever fat stores are available for survival. As such, the fat from marrow can be replaced with an interstitial infiltration of a ground gelatinous substance (acidic mucopolysaccharides). In addition, the intra-peritoneal fat and subcutaneous fat are also utilized. This yields the appearance seen in this case. The marrow in this situation has a much higher T2 signal related to the deposited gelatinous substance. The T1 signal is low but may not be as low as expected related to the underlying nature of the mucopoysaccharides. This condition is also referred to as serous atrophy of the marrow or starvation marrow.

There is no association with the post traumatic bursitis but that is what led the patient to seek medical attention. These patients are however, at times pancytopenic related to the abnormality of the underlying marrow and at times this will require medical attention. In younger women, a triad of eating disorder, amenorrhea, and osteoporosis/stress fractures is a well known triad also known as the female athletic triad. Awareness of this condition may help prevent further health problems.

Case 39 Diagnosis: Bisphosphonate Associated Subtrochanteric Stress Fractures

Bisphosphonate treatment has become a mainstay in the treatment of osteoporosis. More recently PTH analogs have also gained increasing favor. Bisphosphonates work by inhibiting osteoclast activity and inducing apoptosis so that bone is not resorbed. Although extremely useful in patients with osteoporosis to help prevent fractures, adverse reactions do occur.

The most well known is avascular necrosis of the jaw which is associated with high dose intravenous treatment in the cancer patient. In the orthopedic community, bisphosphonate treatment has been associated with subtrochanteric stress fractures and frank, complete fractures. It is postulated that microfractures occur and because of the decreased bone turnover from the bisphosphonate treatment, healing can not occur and these atypical fractures subsequently propagate. There occurrence is however markedly decreased compared to hip fractures and the benefit of treatment is thought to outweigh the risks. That being said, these fractures are difficult to treat and can require subsequent surgery.

Case 38 Diagnosis:

Gout is an arthropathy based on urate crystal deposition. The deposition is typically in a juxta-articular location but may also be within tendons particularly within certain tendons such as the Achilles or knee extensor mechanism. On radiographs, gout produces classically juxta-articular erosions with well defined margins or overhanging edges related to the long standing process and subsequent bone repair. The soft tissue mass or tophus may become dense or frankly calcified related to dystrophic calcification

On MRI, the lesions are classically defined as having low signal intensity on all pulse sequences, but as seen in this example, mild hyperintensity may be encountered. The overall constellation of findings must be taken into account to make the diagnosis. In this case, the soft tissue mass of the left hand was resected and urate crystals were identified via microscopic analysis.

Case 37 Diagnosis: Ollier’s Disease with malignant transformation

A non-hereditary condition of multiple enchondroma or enchondromatosis yielding expansion and deformity of the bone and often rendering short bones or limb length discrepancies. At times the lesions are pedunculated, simulating osteochondroma and referred to as enchondroma protuberans. Lesions tend to predominate in the long bones as well as within the metacarpals/metatarsals. Lesions in the flat bones are not as common. In childhood, lesions are subject to fracture and in adulthood there is an increased risk of malignant transformation. After a child has reached skeletal maturity, the lesions should no longer grow. Continued growth with destruction of the underlying bone indicates malignant transformation which is said to occur in up to 30% of individuals. Typically, malignant transformation is to a chondrosarcoma. Lesions are treated with excision and patients are closely monitored for potential malignant transformation as in this case.

Case 36 Diagnosis: CPPD Arthropathy

Calcium pyrophosphate dihydrate arthropathy (CPPD) is a type of CPPD crystal deposition disease. The CPPD crystals can be deposited in fibrocartilage such as menisci, the TFCC, or pubic symphysis; hyaline cartilage; synovial membrane/synovial fluid; and in tendons and ligaments. The crystals may be seen in the setting of an asymptomatic patient or may yield joint damage leading to an arthropathy similar to degenerative joint disease (DJD) but with distinctive features.

As compared to DJD, large subchondral cysts often predominate and can become so large as to yield pathologic fractures as in this case. In addition, the distribution of joints tends to be somewhat different with increased proclivity in CPPD arthropathy for the wrist and MCP joints as again seen in this case. Although DJD and CPPD arthropathy both heavily affect the knee, in CPPD there is often isolated or severe patellofemoral disease or lateral compartment disease.

Case 35 Diagnosis: ASIS avulsion and posttraumatic subiliacus bursitis

Avulsion injuries at the apophyses are common in the athletic, skeletally immature patient. As the apophyseal plate is less able to sustain load than tendons, the apophyseal plate tends to be the site of failure in the skeletally immature patient. In the pelvis, multiple apophyses are present particularly with injury often seen at the ASIS, anterior inferior iliac spine, ischial tuberosity, and lesser trochanter. Although not discussed in the literature, anecdotally reported are avulsion injuries of the subiliacus muscle yielding posttraumatic bursitis in the skeletally immature patient. This may be similar to abdominal and gluteal muscle injuries sustained at the iliac crest in the skeletally mature patient.

Case 34 Diagnosis: DRUJ Instability

DRUJ (distal radioulnar joint) instability is a complex pathology related to the triangular fibrocartilage complex and particularly the volar and dorsal radioulnar ligaments (vrul and drul). With pronation, the drul will tighten with subsequent “dorsal displacement of the ulna” and with supination the vrul will tighten with subsequent “ volar displacement of the ulna”. With hyperpronation, there is a checkrein via the vrul, but in extreme circumstances this will fail. Failure of the vrul will lead to a persistent posterior positioning of the ulna in a neutral position.

With pronation there may be exaggeration of the posterior positioning or as seen in this case, the loss of competency of the vrul prevents adequate tightening to have the ulna move volarly with supination. Subsequently, the ulna will remain somewhat more posteriorly positioned than the contralateral side. The same pathology, but involving the drul, would occur in a hypersupination injury. The vrul and drul converge at the proximal ulnar attachments and hence all of these structures must be evaluated when assessing for DRUJ instability.

Case 33 Diagnosis: Distal Biceps Rupture

Distal avulsion of the biceps tendon from the radial tuberosity typically occurs in middle aged men who participate in weight lifting. The mechanism is typically eccentric contraction against the flexed elbow where the patient feels a snap or tearing sensation followed by soft tissue swelling at the level of the humerus. The soft tissue swelling relates to muscle retraction as well as soft tissue injury and given the prominence is often identified as a “Popeye” sign. Without repair, the injury can result in prominent weakness of flexion and supination.

Case 32 Diagnosis:

FAI relates to a mismatch at the hip joint either along the femoral side or the acetabular side. Patients typically present with pain exacerbated by certain motions, particularly those related to flexion and internal rotation. Cam lesions involve the femoral side and relate to a loss of the anterior femoral head neck offset. Bone and subchondral cysts form at this location causing subsequent degeneration of the anterosuperior labrum and early cartilage loss.

The pincer lesions relate to ossification along the acetabular side leading to overcoverage of the femoral head. Although anterosuperior labral degeneration is seen, cartilage wear is often found at a contre-coup location of the posterior inferior acetabulum. Pincer pathology is also implicated in the setting of coxa profunda and focal retroversion of the acetabulum. In order to help prevent early degeneration of the hip joint, progression of degeneration, and alleviate patient’s pain surgeons, using new arthroscopic techniques, are able to debride the bone and labrum and restore normal architecture to the hip joint.

Case 31 Diagnosis:

Stress fractures can either be insufficiency fractures or overuse fractures. Previously, a case had demonstrated an insufficiency fracture where abnormal bone had fractured in the setting of normal load. The overuse injury is increased load transmitted to normal bone relating in a stress fracture. One of the classic overuse injuries is of the calcaneus with other bones such as the tibia and distal femur often frequently involved.

The lesion of the distal tibia is an incidental non-ossifying fibroma. The lesion is sclerotic as it has healed. It demonstrates classic features of a metaphyseal, eccentric lesion that is well demarcated and not aggressive nature.

Case 30 Diagnosis:

Facet joints are synovial joints that undergo the same degenerative processes as other joints and inflammatory processes as other joints.  Synovial cysts emanate from multiple joints and in the facet joints of the lumbar spine they can cause mass effect on adjacent, critical neural structures. Most common is that the cysts cause compression of the thecal sac, traversing nerve roots, or of the proximal nerve roots. In this circumstance, somewhat less common, the cyst is causing compression of the nerve root in the neural foramen extending to the exit zone of the neural foramen.

Case 29 Diagnosis: Insufficiency Fracture

Stress fractures are typically related to repetitive force applied to bone. They are typically classified as overuse where there is increased load transmitted to normal bone or insufficiency fractures where there is normal load transmitted to abnormal bone. Insufficiency fractures are frequently seen in the setting of osteoporosis, either postmenopausal, senile, or related to other factors. In the pelvis, the classic sites for insufficiency fractures are the sacral ala, superior acetabulum, pubic symphysis, superior/inferior pubic rami, and the subcapital femoral neck.

Stress fractures can be diagnosed on radiographs by either a thin lucent line in the cortex typically perpendicular to the long axis of the bone, periosteal bone or cortical thickening, or by bands of sclerosis in the medullary cavity. The sensitivity of MRI is vastly superior to radiographs and allows earlier establishment of a diagnosis. On MRI, the fracture line is seen as a low signal band typically surrounded by a prominent amount of increased T2 weighted signal representing marrow edema. Alternative means of diagnosis are on a bone scan where focal, typically oval or band like areas of increased radiotracer uptake are seen at the fracture site.

In this case, there is a clear stress fracture at the superior acetabulum. The low signal band at the femoral neck and mild edema pattern at this location likely represent sequelae of a more remote stress fracture.

Case 28 Diagnosis:

Injuries of the pectoralis major tendon occur as a result of typical eccentric contraction and are seen particularly with lifting as in weight lifting. The muscle has three heads with a clavicular, sternal, and a small abdominal head. The tendon has a complex, bilaminar attachment to the lateral aspect of the intertubercular groove with a superior clavicular and inferior sternal head. Partial tears typically occur at the myotendinous junction and more frequently involve the sternal head. Complete tears occur more frequently at the tendon attachment on the proximal humerus. As the injury occurs at the tendon bone interface, these complete tears frequently produce edema directly about the proximal humerus.

Case 27 Diagnosis:

Periprosthetic left femur fracture eliciting a small adjacent fluid collection containing post traumatic/synovial debris. Additional sacral alar insufficiency fracture.

In the older patient population the presence of osteoporosis makes the bone more predisposed to insufficiency type stress fractures. These fractures occur when normal stress is transmitted to abnormal and in this case weakened bone. In this case the patient recalls focal trauma but at times a defined, inciting event is difficult to recall.

Evaluation of arthroplasties is limited for various reasons in different modalities. Radiographs as in this case may show radiolucency which may represent stress shielding or a focal area of osteolysis. Bone scans are often helpful to locate the site of abnormality but are frequently non-specific. Given the intensity and focal nature of the uptake in this case, the findings would be most consistent with a fracture. MRI is hampered by field inhomogeneity, difference in magnetization, and mismapping artifacts yielding areas of signal void and spurious high signal. Multiple technical parameters are employed to overcome these limitations. The linear bands representing fractures and the surrounding edema and fluid collection can be difficult to perceive and quite subtle.

Case 26 Diagnosis: Rheumatoid Arthritis

Rheumatoid arthritis is an inflammatory arthropathy that yields synovial proliferation and synovitis, accounting for the dense synovitis seen on the MRI. Inflammation leads to erosion of bone as well as cartilage loss, accounting for the joint space loss and articular findings seen well on both the CT and MRI. Rheumatoid is a diffuse process and, as such, typically involves joints in a symmetric pattern with uniform joint space narrowing.

This uniform joint space narrowing is what leads to the concentric or axial type narrowing seen of the hip joints in rheumatoid arthritis. The finding of protrusio is not unique to rheumatoid but is related to the joint remodeling often seen in inflammatory arthropathies. Although strictly diagnosed via medial displacement of the acetabular line relative to the ilioischial line, an easier substitute is the femoral head crossing the ilioischial line.

Case 25 Diagnosis: Hemophilia

Hemophilia is a classically X-linked recessive disease affecting men where there is deficiency of a clotting factor (Factor VIII or IX) that  leads to repetitive episodes of bleeding into the joint or hemarthrosis with subsequent hemosiderin deposition and synovial proliferation. This in turn leads to erosion of the cartilage, subchondral cystic change, and hemophilic arthropathy. Secondary degenerative changes are frequently seen as well.

This underlying pathology accounts for the findings on the MRI of the thickened synovium, subchondral cysts, and bony erosions. The extensive cartilage loss is seen well particularly on the axial images of the current case. The blooming artifact or exaggerated low signal within the synovium relates to the physics in the acquisition of the gradient echo sequence and is seen in the presence of particularly pigment or hemosiderin and to a lesser degree calcification. Hemophilia has a proclivity to affect the hinge joints (elbow, ankle, and knee) secondary to the tendency for hemarthrosis in these joints.

Case 24 Diagnosis: Gaucher's Disease

Gaucher’s disease is a lysosomal storage disorder where the patient lacks the enzyme glucocerebrosidase that leads to accumulation of glucocerebroside within the lysosomes of macrophages. These Gaucher cells tend to deposit in the organs of the reticuloendothelial system such as the liver, spleen, and bone marrow. Accumulation in the bone marrow leads to osteopenia, or foci, of radiolucency, which can also predispose to fracture.

Gaucher’s also predisposes to bone infarcts, which can be seen in the medullary space or ends of the bone. Accumulation within the marrow can also cause expansion of the bone yielding an Erlenmeyer flask deformity. H-shaped vertebrae are thought to be secondary to an ischemic growth disturbance at the central portion of the chondro-osseous junction.

Replacement of the marrow tends to yield low signal T1 and low signal T2 marrow, but this may be patchy in appearance. Areas of increased T2 signal may be seen in the setting of infarction and a more “active marrow process” such as ongoing ischemia.

Case 23 Findings/Diagnosis: Lunatotriquetral Ligament Disruption with VISI

Radiographs and MR images demonstrate a volar flexion of the lunate on sagittal/lateral views and an abnormal triangular configuration of the lunate on the frontal radiograph.  MR images demonstrate a lack of the normal low signal intensity lunatotriquetral ligament and a high signal, granulation tissue is interposed at the site of the previous ligament.  Axial images demonstrate the high signal of the lunotriquetral interval spanning from dorsal to volar.

The lunatotriquetal (LT) ligament is one of the main intrinsic ligaments of the wrist along with the scapholunate (SL) ligament. The LT ligament is a complex structure with the volar fibers providing the majority of functional stability. In the setting of a lunatotriquetral ligament injury, a volar intercalated segment instability can sometimes be yielded. The proximal row of the wrist functions as a synchronous. The assessment of volar intercalated segment instability is provided on a sagittal or lateral image by evaluating the capitolunate and scapholunate angles. The normal capitolunate angle of 0 to 20 degrees is increased and the scapholunate angle of 30 to 60 degrees is decreased secondary to the palmar angulation of the lunate. On the contrary, DISI abnormality yields an increase in both the scapholunate and capitolunate angles.

Case 22 Finding/Diagnosis: Meniscal Tear

Multiple planes of imaging demonstrate a displaced lateral meniscal tear with the posterior horn and body displaced into the intercondylar notch. This is in the setting of a long standing ACL disruption with anterior translation of the tibia and focal scarring at the synovial reflection of the ACL or a so called cyclops lesion.

Discussion:Tears oriented along the longitudinal axis of the meniscus may displace either into the intercondylar notch, anteriorly, or both. Meniscal fragments displaced into the intercondylar notch are rare on the lateral side because of the ACL. In the setting of a disrupted ACL, the meniscal tissue may displace into the intercondylar notch as in this case. About the ACL is a synovial reflection accounting for its intracapsular, extrasynovial position. In the setting typically of ACL reconstruction, there may be prominent focal scar tissue at the reflection yielding a block to extension. The arthroscopist sees this as a focal nodular density similar to the one eyed cyclops; hence the term cyclops lesion. Although not as common, a similar focal fibroproliferative process can occur in the setting of a long standing ACL tear without previous reconstruction as in this case.

Case 21 Diagnosis: Intermetatarsal Bursitis

In the forefoot, where the digital nerves traverse the deep transverse metatarsal ligament, there is often entrapment with fibrosis. This leads to a Morton’s neuroma. However, also at this location is the intermetatarsal bursa, which usually contains a minimal amount of fluid. With irritation of the nerve or directly of the bursae, an increasing amount of fluid may yield a pathological intermetatarsal bursitis. This may contain synovitis, as is seen in this case. Intemetatarsal bursitis is frequently seen with an underlying Morton’s neuroma, but may be seen in isolation, also as seen in this case.

Case 20 Diagnosis: Juvenile Chronic Arthritis (JCA)

JCA is a heterogeneous collection of inflammatory arthropathies occurring in patients less than 16 years of age. It is typically divided into juvenile onset ankylosing spondylitis, juvenile onset psoriasis/inflammatory bowel disease, juvenile onset adult type RA, and Still’s disease. Still’s disease is then separated into pauciarticular, polyarticular, or systemic variants. Systemic implies serositis, renal disease, hepatosplenomegaly, and lymphadenopathy. The radiologic findings of JCA are similar to adult onset RA except that typically JCA will involve the larger joints first (knees, ankles, and elbow) and the smaller joints of the hand and wrist later. The early findings of JCA are pronounced osteopenia and periarticular soft tissue swelling. With continued hyperemia to the joint there is a ballooning of the ends of the bones, and as the disease progresses, erosions and then ankylosis become present.

Case 19 Diagnosis: Bucket Handle Tear

Bucket handle tear of the medial meniscus in the setting of a chronic disruption of the ACL. Additional anatomic variant of an oblique meniscomeniscal ligament that extends from the posterior horn of the lateral meniscus to the anterior horn of the medial meniscus. The bucket handle tear is a longitudinal tear with displacement of the meniscal fragment within the intercondylar notch. In a small percentage of people, 1 to 4 %, apart from the transverse meniscal ligament, meniscofemoral ligaments, and meniscotibial ligament, an oblique meniscomeniscal ligament can occur. This courses from the posterior horn of one meniscus to the anterior horn of the other. This can be confused with a bucket handle tear and is crucial to be identified prior to surgery to prevent inappropriate resection.

Case 18 Diagnosis: Tarsal Coalition

Tarsal coalition is an abnormal fusion of the tarsal bones. The fusion is either osseous or non-osseous (fibrous/cartilaginous). Coalitions can be congenital, related to trauma, or secondary to multiple other conditions. Tarsal coalition is one cause of a congenital rigid flatfoot with congenital vertical talus being the other. On imaging, there is bony or fibrocartilaginous tissue fusing the bones with irregular surfaces at the site of the fusion. Edema is elicited secondary to abnormal mechanics and can generate pain. Tarsal coalitions are bilateral 50-60% of the time.

Case 17 Diagnosis: Aneurysmal Bone Cyst

Aneurysmal Bone Cyst, or ABC, is described histologically as an intraosseous vascular malformation with blood filled spaces. This accounts for the multiple fluid fluid levels seen on cross sectional imaging. Approximately 1/3 of ABC’s occur in the setting of another primary tumor with secondary ABC formation. Periosteal reaction does not occur typically unless there is associated trauma. Lesions are classically expansile, eccentric, and metaphyseal. Diaphyseal and epiphyseal extension does occur.

Case 16 Diagnosis: Stump Neuroma

Stump neuroma represents a disorganized proliferation of nerve fascicles and fibrosis at the site of a transected nerve in the setting of amputation. Stump neuromas are thought to play a part not only in the localized phenomenon of stump pain but in a more globalized phantom pain of the amputated extremity. The role of peripheral vs. central neurologic factors in the etiology of these phenomena is still to be explained. Recent therapies have utilized neurosclerosing agents such as phenol with limited success.

Case 15 Diagnosis: Ankylosing Spondylitis with insufficiency fracture

Ankylosing spondylitis has been previously described in an aforementioned case and again represents one of the seronegative arthropathies which causes prominent bone production within the axial skeleton or at the entheses. Although prominent bone is present, it is more predisposed to fracture secondary to rigidity, and fractures often will occur with minor trauma. Pseudarthrosis in ankylosing spondylitis is another common complication thought to represent sequelae of localized inflammatory process centered at the disc space or of previously undiagnosed minor trauma.

Case 14 Diagnosis: Myositis Ossificans

Muscle that has sustained trauma undergoes a process of formation of ossification in the musculature. In the first 8 weeks following the injury on MRI, a heterogeneous mass is frequently seen with a profound amount of surrounding edema. With time, a peripheral low signal intensity rim forms corresponding to peripheral ossification. In its early forms, the peripheral ossification may have a somewhat amorphous appearance on CT or radiograph without clear trabecular formation.

Frequently, patients do not recall a discrete event, and with aging, less significant trauma is needed to cause these changes. Ultrasound is useful to demonstrate acoustic shadowing indicating a dense substance (often calcification, ossification, or marked fibrosis). Ultrasound can also be used, as in this case, for biopsy to confirm the diagnosis.

*Special thanks to the Department of Pathology for their assistance in this diagnosis.

Case 13 Diagnosis: CRMO

Chronic recurrent multifocal osteomyelitis (CRMO) is a poorly understood inflammatory process that overlaps with other inflammatory processes such as SAPHO and the seronegative arthropathies. SAPHO (synovitis, acne, pustulosis, hyperostosis, and osteitis) is more typical of adults while CRMO predominates in children. The delineation between these syndromes is not clear at the present time. CRMO is intermittent with exacerbations and typically has a good prognosis although medical management is somewhat limited at the present.

Case 12 Diagnosis: Amyloidosis

Amyloidosis can occur as a primary, idiopathic process but is more commonly seen in the setting of renal pathology or multiple myeloma. There are multiple types of amyloid that can be deposited about the musculoskeletal system. Deposition is typically in the periarticular soft tissue, within tendons or ligaments, or within the bones about a joint. Deposition of the ossesous structures is seen as nonspecific radiolucencies which can appear as soft tissue or cyst like lesions on cross sectional imaging. There is classically a relative preservation of the joint space which on occasion may be narrowed from a long standing process or secondary processes such as osteonecrosis with secondary arthrosis.

Case 11 Diagnosis: Insufficiency Fracture with post-traumatic osteolysis

Post traumatic osteolysis is commonly thought of as occurring in the distal clavicle secondary to trauma but is becoming more prominent in the pubis as the population ages. It most typically occurs, as in this case, in post menopausal women and typically with concomitant sacral insufficiency fractures. The differential diagnosis includes infection or tumor, although as in this case, a fluid collection can be present and not a soft tissue component, mitigating against tumor. Biopsy was performed with cultures obtained, both of which were negative.

Case 10 Diagnosis: Hemangioma

Osseous hemangioma is a common vascular tumor most frequently encountered in the vertebral body of the lower thoracic or lumbar vertebrae. Imaging findings reflect prominent bony resorption of the majority of the osseous trabeculae with the remaining trabeculae demonstrating a thickened, coarsened architecture frequently referred to as “corduroy” or “polka dot." Often will be associated with focal areas of fatty signal (high T1, high T2, low IR) and typically show no uptake of radionuclide on bone scan but may demonstrate up to moderate uptake.

Case 9 Diagnosis: Lisfranc Ligament Disruption

Comments: High resolution MRI demonstrates a high grade partial disruption of the Lisfranc ligament in the first case and a complete disruption in the second case. The ligament acts as the keystone in support of the midfoot as it courses from the base of the second metatarsal to the medial cuneiform. Recent literature has helped substantiate that any offset is probably amenable to surgical fixation as malalignment will precipitate pain and early, profound arthrosis.

Case 8 Diagnosis: Melorheostosis

Comments: A benign bony proliferative process typically identified in early adulthood but sometimes becoming symptomatic only later in adult life when there is pain and limitation of joint movement secondary to bony encroachment. Additionally, there may be adjacent soft tissue inflammation as in this case which is precipitating an iliotibial band friction type syndrome. There is a typical candle wax cortical thickening and trabecular condensation in a sclerotomal (distribution of the skeleton supplied by a sensory nerve) distribution. In approximately one quarter of the cases, soft tissue masses with calcification are seen.

Case 7 Diagnosis: Infectious Bursitis/Osteomyelitis

Comments: A true bursa such as the olecranon bursa is a synovial lined sac that can become inflamed from infectious and non infectious entities. In either situation, the underlying bone is susceptible to the same aggressive process. MRI is highly suggestive for infection when a marrow edema pattern is present in a diffuse pattern with adjacent soft tissue edema. Thick, enhancing soft tissue or bony lesions in the setting of possible infection are essentially diagnostic. The triceps destruction with avulsion is just a “collateral” injury.

Case 6 Diagnosis: Scleroderma

Comments: Connective tissue disorder more prevalent in women than men that produces symptomatology generally in the second to third decade and continues to progress. Underlying pathology is a fibrosis that affects multiple organ systems. Classic findings include myositis of the proximal musculature that later precipitates fatty atrophy and large, conglomerate tumorlike or sheet like calcification of the soft tissue. It is frequently associated with other syndromes and produces an interstitial lung disease, preferentially at the lung bases, and esophageal dysmotility or a patulous esophagus.

Case 5 Diagnosis: Ankylosing Spondylitis

Seronegative arthropathy that produces syndesmophytes (ossification of the annulus fibrosus) that start at the thoracolumbar junction and extend cranially and caudally, sacroiliitis with eventual fusion, and enthesopathic change. In cases of marked disease and later in the time course dural ectasia may become manifest with associated cauda equina syndrome.

Case 4 Diagnosis: Paget Sarcoma

Comments: Paget disease is a fairly common disease of the older patient population classically manifest by cortical thickening, enlarged bone, and thickened, coarsened trabeculae. Multiple complications are well known including fracture, cranial nerve impingement, and malignant transformation. Most commonly this involves degeneration to an osteosarcoma as in this case but may alternatively be a fibrosarcoma, malignant fibrous histiocytoma, or chondrosarcoma.

Case 3 Diagnosis: Osteoid Osteoma

Bony lesion of osteoid and immature bone that incites an adjacent reactive bony/inflammatory response secondary to prostaglandin release. Typically in younger patients (5-25 ) and with a classic clinical pattern of night time pain alleviated with aspirin. Classified as cortical, cancellous, and subperiosteal. This case presents the rarest type, a subperiosteal lesion. Current standard of care is radiofrequency ablation if possible or resection.

Case 2 Diagnosis: Bone Infarcts in Systemic Lupus Erythematosus

Bone infarcts are seen in a multitude of conditions, predominantly at our institution from previous trauma, steroid use, and in the setting of a vasculitis. Infarcts associated with Lupus are thought to be in part secondary to steroid treatment but also secondary to the underlying vasculitis that afflicts multiple organ systems in these patients. The nonerosive subluxation, or Jacoud type arthropathy of the hand is classic for SLE, and helps in narrowing the differential of a bone infarct.

Case 1 Diagnosis: Osteofibrous Dysplasia

Osteofibrous dysplasia is a rare bone tumor of the tubular bones, most commonly in the anterior cortex of the tibia, which is often referred to as an ossifying fibroma of the tubular bones. Thought to exist within a spectrum of benign to malignant with adamantinoma. Treatment is controversial but follow up radiographs and careful observation is paramount to asses for possible degeneration to adamantinoma.