Avascular Necrosis of the Hip

Avascular Necrosis of the Hip

Avascular necrosis of the hip is an often missed diagnosis. It is also known as osteonecrosis . Similar to the scaphoid, the hip is extremely susceptible to this disease because of its tenuous blood supply.

The blood supply of the hip is easily disrupted, often leaving the proximal portion of the bone without nutrition, thereby leading to osteonecrosis.

Avascular necrosis of the hip is a disease of the fourth and fifth decades of life and is more common in men, with an 8:1 male-to-female preponderance, except for patients with avascular necrosis of the hip secondary to collagen-vascular disease. The disease is bilateral in 50% to 55% of cases.

Predisposing factors to avascular necrosis of the hip are listed in below and include trauma to the proximal femur and acetabulum; corticosteroid use; Cushing disease; alcohol abuse; connective tissue diseases, especially systemic lupus erythematosus; osteomyelitis; human immunodeficiency virus (HIV); organ transplantation; Legg-Calvé-Perthes disease; hemoglobinopathies, including sickle cell disease; hyperlipidemia; gout; renal failure; pregnancy; and radiation therapy involving the femoral head.

A patient with avascular necrosis of the hip reports pain over the affected hip or hips, which may radiate into the groin, buttocks, and proximal lower extremity. The pain is deep and aching, and the patient often reports a catching sensation with range of motion of the affected hip or hips. Range of motion decreases as the disease progresses.

Predisposing Factors for Avascular Necrosis of the Hip

Trauma to proximal femur and acetabulum
Corticosteroid use
Cushing disease
Alcohol abuse
Connective tissue diseases, especially systemic lupus erythematosus
Osteomyelitis
Human immunodeficiency virus
Organ transplantation
Legg-Calvé-Perthes disease
Hemoglobinopathies, including sickle cell disease
Hyperlipidemia
Gout
Renal failure
Pregnancy
Radiation therapy

Signs and Symptoms

Physical examination of patients with avascular necrosis of the hip reveals pain to deep palpation of the hip joint. The pain becomes worse with passive range of motion and weight bearing on a single extremity. A click or crepitus may be appreciated by the examiner when putting the hip joint through range of motion. A Trendelenburg gait may be noted, and decreased range of motion is invariably present.

How is Avascular Necrosis of the Hip diagnosed?

Plain radiographs are indicated in all patients with avascular necrosis of the hip to rule out underlying occult bony pathological processes and identify sclerosis and fragmentation of the femoral head, although early in the course of the disease, plain radiographs are unreliable.

Based on the patient’s clinical presentation, additional tests, including complete blood cell count, uric acid, erythrocyte sedimentation rate, and antinuclear antibody testing, may be indicated. Magnetic resonance imaging (MRI) of the hip is indicated in all patients suspected to have avascular necrosis of the hip or if other causes of joint instability, infection, or tumor are suspected.

Administration of gadolinium followed by postcontrast imaging may help delineate the adequacy of blood supply, with contrast enhancement of the proximal hip being a good prognostic sign. Computed tomography scanning may provide additional information regarding the condition of the hip joint and guide treatment decisions. Electromyography is indicated if coexistent lumbar radiculopathy, plexopathy, or both are suspected. A gentle injection of the hip joint with small volumes of local anesthetic provides immediate improvement of the pain and helps show the nidus of the patient’s pain is, in fact, the hip. Ultimately, total joint replacement is required in most patients with avascular necrosis of the hip.

Differential Diagnosis

Coexistent arthritis and gout of the hip joints, bursitis, and tendinitis may coexist with avascular necrosis of the hips and exacerbate the pain and disability of the patient. Tears of the labrum, ligament tears, bone cysts, bone contusions, bone fractures, and occult metastatic disease also may mimic the pain of avascular necrosis of the hip.

Treatment

Initial treatment of the pain and functional disability associated with avascular necrosis of the hip should include a combination of nonsteroidal antiinflammatory drugs (NSAIDs) or cyclooxygenase-2 (COX-2) inhibitors and decreased weight bearing of the affected hip or hips. Local application of heat and cold may be beneficial. For patients who do not respond to these treatment modalities, an injection of a local anesthetic into the hip joint may be a reasonable next step to provide palliation of acute pain. Vigorous exercises should be avoided because they would exacerbate the patient’s symptoms. Ultimately, surgical repair in the form of total joint arthroplasty is the treatment of choice.

Complications and Pitfalls

Failure to treat significant avascular necrosis of the hip surgically usually results in continued pain and disability and in most patients leads to ongoing damage to the hip. Injection of the joint with local anesthetic is a relatively safe technique if the clinician is attentive to detail, specifically using small amounts of local anesthetic and avoiding high injection pressures, which may damage the joint further. Another complication of this injection technique is infection. This complication should be exceedingly rare if the clinician adheres to strict aseptic technique. Approximately 25% of patients report a transient increase in pain after this injection technique and should be warned of such.

Clinical Pearls

Avascular necrosis of the hip is a diagnosis that is often missed, leading to much unnecessary pain and disability. The clinician should include avascular necrosis of the hip in the differential diagnosis with all patients with hip pain, especially if any of the predisposing factors listed below are present. Coexistent arthritis, tendinitis, and gout may contribute to the pain and may require additional treatment. The use of physical modalities, including local heat and cold and decreased weight bearing, may provide symptomatic relief. Vigorous exercises should be avoided because they would exacerbate the symptoms and may cause further damage to the hip. Simple analgesics and NSAIDs may be used concurrently with this injection technique.

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