Diagnosis Index

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 hemorraghic 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. Atrhroscopic 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 ganlion 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 avulation is a Bankart variant or variant of an anteroinferor 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 tendonitits. 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 diruption 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 anterorsuperior 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 glucocerbrosidase 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.

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