Avascular necrosis (AVN), also known as osteonecrosis of the hip, is a condition that results from a significant loss of blood supply to an area of the femoral head, the top of the thighbone where it fits in the hip socket. This disabling condition can lead to collapse of the femoral head and loss of joint congruity. Without blood, the head of the femur dies and collapses, making hip movement painful and may lead to rapid progression of hip joint arthritis.
Bony abnormalities refers to hip conditions involving irregularities in the hip joint such as femoroacetabular impingement (FAI), cam impingement, pincer lesions, and dysplasia.
It has been well documented that nearly 90 percent of all young patients with labral pathology have associated bony abnormalities and that conditions such as hip impingement and dysplasia are the two most common underlying factors associated with the development of osteoarthritis in the hip. As the medical profession’s knowledge about the mechanics of the hip has grown, it has become clear that there are often times complex combinations of both dynamic and static mechanical factors that cause damage to the labrum and eventual hip arthritis.
Throughout the body, small sacs called bursae, sometimes filled with a little fluid, act as cushions between bones, tendons and muscles. Several bursae are located around the outer area of the hip, near the portion of the thighbone (femur) called the greater trochanter (tro-KAN-ter). The greater trochanter is a broad, flat area of bone that anchors several large muscles. An inflammation of a trochanteric bursa is a common cause of hip pain. Learn more about bursitis of the hip.
Articular cartilage, the soft tissue coating the surfaces in the body, allows for the pain-free motion of the joints. Injuries to, or loss of, the articular cartilage exposes the underlying “subchondral” bone surface. This region is richly innervated and as such is the primary source of pain when there is loss of the articular cartilage. Treatment options include non-operative regimens such as diet, exercise and avoidance of impact activities. The role for cartilage enhancing agents such as oral supplements as well as injections of synovial fluid analogs is not entirely clear at this time. Surgical treatments for articular cartilage loss are wide-ranging, and include attempts to stimulate the joint to make a reparative type of cartilage through the process of microfracture, tissue banked cartilage transplantation for small, isolated areas of cartilage loss, joint replacement surgery may be necessary when there is full thickness cartilage loss from large areas of the weight bearing surface of the joint.
The labrum, the ring of soft tissue that follows the outside rim of the socket of the hip joint, helps to cushion the joint and works a little like a suction cup to help hold the hip joint together.
Pain with hyperflexion, internal rotation, and adduction (impingement position) occurs in the majority of patients suffering from a detachment of the hip labrum. Labral tears are typically the result of some underlying etiology including: traumatic subluxation or dislocation, atraumatic microinstability or capsular laxity, underlying bony abnormalities such as femoroacetabular impingement or dysplasia, and psoas impingement or symptomatic internal coxa saltans.
Disorders about the hip can be thought of as either related directly to the joint (intra-articular) or to conditions which are outside of the joint (external to the joint capsule) known as extra-articular. These can include tendon injuries, muscular injuries, and nerve entrapment syndromes, as well as non-orthopedic conditions such as hernias, pelvic floor disorders, or genitourinary conditions.
Many mechanical factors are related to the development of hip joint damage and pain. The position in which the femoral head sits in the hip joint is defined as femoral torsion. If you imagine the center of the femoral head pointing directly to the center of the acetabulum, this is defined as neutral femoral torsion. When the center of the femoral head points more toward the anterior aspect of the hip joint, then it is known as anteversion. If the center of the femoral head points to the back of the hip joint, it is known as retroversion. Excessive femoral anteversion and retroversion lead to symptomatic, painful hips and progressive cartilage wear. A patient suffering from excessive torsion may consider femoral rotational osteotomies as a long-term solution.
Hip dysplasia is a congenital condition of the hip joint socket, or acetabulum, where the cavity in the pelvic bone that forms the hip socket has limited coverage of the head of the femur (the round ball that fits inside socket). To compensate for this loss of coverage, the body forms more soft labrum tissue, the fibrous cartilage that rings the acetabulum. As a result, the labrum becomes overloaded and predisposed to tearing. Learn more about hip dysplasia.
Types of hip dysplasia
Femoroacetabular impingement (FAI) occurs when the ball (head of the femur) does not have its full range of motion within the socket (acetabulum of the pelvis). This causes a decreased range of hip joint motion, in addition to pain. Most commonly, FAI is a result of excess bone that has formed around the head and/or neck of the femur, otherwise known as “cam”-type impingement. FAI also commonly results from an overgrowth of the acetabular (socket) rim, otherwise known as “pincer”-type impingement, or when the socket is angled in such a way that abnormal impact occurs between the femur and the rim of the acetabulum.
When the extra bone on the femoral head and/or neck hits the rim of the acetabulum, the cartilage and labrum that line the acetabulum can be damaged. The extra bone can appear on x-rays as a seemingly very small “bump.” However, when the bump repeatedly rubs against the cartilage and labrum (which serve to cushion the impact between the ball and socket), the cartilage and labrum can fray or tear, resulting in pain. As more cartilage and labrum is lost, the bone of the femur will impact with the bone of the pelvis. This “bone on bone” motion is most commonly known as arthritis.
Athletes with femoroacetabular impingement usually complain of anterior groin pain that worsens with hip flexion, internal rotation, and adduction. Good results have been reported in the literature for patients treated arthroscopically for labral tears and associated femoroacetabular impingement, with as high as 93 percent of patients able to return to sports and 78 percent able to remain active at 1.5 years after surgery. For more information, see Hip Mobility and Hip Arthroscopy: A Patient's Guide to Correcting Femoro-acetabular Impingement.
Types of hip impingement
Osteoarthritis is a disease in which the spongy tissue that coats the ends of bones and joints (also known as cartilage) breaks down. Normally, damaged cartilage repairs itself as older cartilage is degraded. When the balance between degradation and repair is thrown off, cartilage breakdown occurs and damage to bone results. The outcome can be painful and cause tender, creaky joints and limitations in joint movement. Osteoarthritis is the most common form of arthritis and affects more than 20 million Americans, mostly adults over the age of 65.
The most common symptom of osteoarthritis is pain and stiffness in the joint. Sometimes there is swelling in the joint as well as downward radiating pain; sometimes the pain is so severe that it awakens a sufferer from sleep. Learn more about the Osteoarthritis Initiative at HSS.
Often times hip pathology may present as “intractable” knee pain. This is called referred pain because of the close proximity of the femoral nerve to the anterior hip capsule. Severe knee pain in a patient with an apparent “normal knee” exam warrants a close inspection of the hip.
The socket of the hip joint (acetabulum) has a rim of rubbery fibrocartilage called the labrum. In addition to providing additional cushioning at the rim of the joint, the labrum acts as a gasket, sealing in fluid. This allows the joint fluid within the femoral head to be maintained, protecting the articular cartilage layers of the femur and acetabulum so that the ball of the thighbone (femur) moves easily and comfortably in the hip socket.
A tear of the labrum can occur from an injury, repetitive motion that causes wear, or degeneration from osteoarthritis. Often a person will have a labral tear, experience no symptoms, and require no treatment. In other cases, there may be pain or a “catching” feeling in the hip joint that may require treatment in the form of physical therapy, medications or surgery.
The close anatomic relationship of the hip joint to the lower, lumbosacral spine can often present a challenge in determining the primary cause of pain. Most “true” hip disorders are manifest by anterior hip pain (often called groin pain) while posterior pain/buttock pain is, in general, a symptom of lumbar spine problems. However, there are many instances where true hip pathology presents as lateral hip pain or even buttock/gluteal pain. In addition, not all groin pain is the result of hip pathology; upper lumbar root impingement, for example, will present as groin discomfort. It is therefore key to make sure that a complete lumbar exam is performed on a new patient seeking a hip evaluation.
Muscle strains in the hip area occur when a stretched muscle is forced to contract suddenly. A fall or direct blow to the muscle, or overstretching and overuse can tear muscle fibers, resulting in a strain. The risk of muscle strain increases with prior injury to the area, improper warm up before exercising or attempting to do too much too quickly. Strains may be mild, moderate or severe, depending on the extent of the injury.
Tendonitis (also known as tendinitis) is a general term used to describe inflammation associated with a tendon. Tendons connect muscles to bone, and inflammation of these rope-like tissues is the most common cause of soft-tissue pain. Tendonitis differs from arthritis, which refers to inflammation of a joint. The onset of tendonitis can usually be attributed to overuse of the associated area. With age, repetitive motion can injure the tendon where it attaches to the bone, promoting an inflammatory response by the body. This inflammation can cause “pain on motion,” swelling, warmth, tenderness, and redness. This latter symptom is called “erythema” and refers to the dilation of small surface blood vessels, capillaries as a result of the inflammatory process.
This condition, which occurs during childhood and adolescence, involves the stopping of blood flow to the femoral head, leading to abnormalities of the femoral head anatomy. The rounded head of the femur dies, leading to softening of the bone and eventual collapse, leaving the area inflamed and irritated.
Treatment options typically require a period of bed rest, possible traction, and using crutches for limited weight bearing during the acute phase. Surgical options include: core decompression, hip arthroscopy, hip osteotomy, and in severe cases, total joint arthroplasty.
For more detail about this condition, see Legg-Calvé-Perthes Disease: An Overview.
Hip ligaments strengthen the articular capsule of the hip stabilizing the joint. Ligament strains or ruptures occur if the joint is twisted or overstretched. Usually a “snapping” or “cracking” occurs when a ligament ruptures, which is followed by bruising, swelling and pain. Movement of the involved joint will usually be limited due to pain.
Femoroacetabular impingement (FAI) occurs when the ball (head of the femur) does not have its full range of motion, and results in pinching or friction in the hip joint, which may cause damage to the labrum (a fibrous cartilage that lines the outer edge of the socket) and/or the articular cartilage. Decompression of the femoral-head neck junction restores the normal head neck junction and provides the femoral head within the acetabulum with full flexion and rotation.
Synovitis is the term for inflammation of the synovium, the inner layer of the joint capsule made up of a glossy, highly vascular inside layer of loose connective tissue. Most hip conditions overload this capsule causing its inflammation.
Slipped capital femoral epiphysis (SCFE) is the most common hip disorder among early teenagers. It occurs when the cartilage growth plate (epiphysis) at the top of the teen’s thighbone (femoral head) slips out of place. In a growing child, the plate is what controls the way the top of the thighbone grows. Most often, it occurs during a period of accelerated growth, shortly after the onset of puberty.
The occasional “snapping” that can be heard when walking or swinging one’s leg around results from the movement of a muscle or tendon (the tough, fibrous tissue that connects muscle to bone) over a bony structure. In the hip, the most common site is at the outer side where a band of connective tissue (the iliotibial band) passes over the broad, flat portion of the thighbone known as the greater trochanter (tro-KAN-ter). The snapping can also occur from the back-and-forth motion that takes place when the tendon, running from the inside of the thighbone up through the pelvis, shifts across the head of the thighbone. A tear in the cartilage or some bone debris in the hip joint can also cause a snapping or clicking sensation.
Tendinopathies refer to disorders of the tendon. Tendons are the soft tissues that connect muscle to bones. There can be conditions in which the tendon is inflamed (tendonitis), has some degree of degeneration and tearing (tendinosis), or is completely torn. The majority of these conditions respond to nonoperative treatments with rest, NSAID’s and physical therapy.
Version refers to the angle of femoral neck in relationship to the shaft of the femur. Extreme excessive version may require surgical correction, such as a procedure known as an osteotomy, which involves breaking and realigning the femur.
Femoral anteversion is a condition in which the femoral neck is excessively rotated forward on the femoral shaft. Excessive anteversion overloads the anterior structures of the hip joint, including the labrum and capsule, and can cause snapping.
Femoral retroversion is a condition in which the femoral neck is rotated backward on the femoral shaft. Femoral retroversion can result in the crushing of the labrum.