• Usually presents with pain upon weight-bearing and motion of the affected joint.
  
• The most common site is the femoral head, but the distal femur, ankles, shoulders, wrists and elbows may also be affected.
  
• There are many predisposing conditions but glucocorticoid therapy, alcohol abuse, and trauma account for the great majority of cases.
  
• MRI has sensitivity for early disease and can detect characteristic abnormalities before radiographic changes are apparent.

Osteonecrosis results from impaired delivery of adequate oxygen to underlying bone. It typically affects the poorly vascularized fatty marrow and is characterized by areas of dead marrow and trabecular bone extending to the subchondral plate. Other terms frequently used for this condition are “ischemic necrosis,” “avascular necrosis” and “aseptic necrosis.” Osteochondritis dessicans and Kienböck disease are forms of osteonecrosis.

The femoral head is particularly susceptible to osteonecrosis. Typically, osteonecrosis of the femoral head develops in the anterolateral aspect just below the weight-bearing articular surface; this is the site of greatest mechanical stress. Once radiographic abnormalities are apparent, collapse of the femoral head is usually inevitable, at intervals ranging from weeks to years.

Osteonecrosis is not a discrete disease but represents the final common pathway of multiple conditions, most of which result in impaired blood supply to bone. Proposed mechanisms include occlusion of smaller arteries of the femoral head by lipid droplets, sickled red blood cells, or nitrogen bubbles from caisson disease. Alternatively, structural damage to the arterial or venous walls from trauma, vasculitis, radiation, or release of vasoactive substances may lead to ischemia. In some conditions, increased intraosseous pressure from enlargement of intramedullary fat cells or osteocytes may play a role. Through one or more of these pathways, osteonecrosis begins with interruption of the blood supply to bone; subsequently, the adjacent area becomes hyperemic, leading to demineralization, trabecular thinning and, if stressed, bony collapse. The process is usually progressive, resulting in joint destruction within 3–5 years if left untreated.

Elderly persons seem to be at decreased risk for developing osteonecrosis. In this age group, fat cells become smaller. The space between fat cells fills with a loose reticulum and mucoid fluid, resistant to ischemic necrosis. This is termed “gelatinous marrow,” and even in the presence of increased intramedullary pressure, interstitial fluid is able to escape into the blood vessels, leaving the spaces free to absorb additional fluid.

The true prevalence of osteonecrosis is unknown, but it is estimated that there are approximately 10,000 to 20,000 new cases annually in the United States. Osteonecrosis is the underlying diagnosis in approximately 10% of all total hip replacements. For the most part, osteonecrosis affects the epiphyses of the long bones, such as the femoral and humeral heads, but other bones (eg, carpal and tarsal) can also be affected. The disease occurs more frequently in men than women, with the overall male to female ratio in the range of 8:1. The age distribution is wide, but most patients are younger than age 50 at the time of diagnosis. The average age of female cases exceeds that of males by almost 10 years.

Osteonecrosis can develop in a variety of clinical settings (Table 59–1). Trauma, glucocorticoid use, and excessive alcohol intake account for more than 90% of adult cases in the United States.

Trauma that results in the dislocation or fracture of the femoral neck, especially in the subcapital region, can interrupt the blood supply to the femoral head, leading to ischemia and osteonecrosis. Osteonecrosis can occur within 8 hours of traumatic disruption of the blood supply. The superior retinacular vessels and the nutrient artery can be damaged as they enter the femur. Intracapsular hematoma increases intracapsular pressure, which can cause tamponade of the joint capsule. The incidence of osteonecrosis in such cases, which is at least 30%, increases for badly displaced fractures, particularly in young adults. Intertrochanteric and extracapsular fractures of the femur rarely lead to osteonecrosis. Following hip dislocation, circulation is interrupted because of tears of the artery of the ligamentum teres. Tearing of the joint capsule compromises the vessels within the capsular reflections. Osteonecrosis following subcapital fractures of the femur may develop as late as 10 years following the fracture. Dislocation of the hip is much less common than hip fracture, but the incidence of osteonecrosis is quite high if reduction is delayed by more than 6 hours. A fracture of the wrist (scaphoid or lunate) is associated with an increased risk of osteonecrosis. Osteonecrosis of the lunate, known as Kienböck disease, may occur without an identifiable event.

Many studies have linked glucocorticoid use to the development of osteonecrosis. The incidence of osteonecrosis among patients treated with glucocorticoids is affected by the dose and duration of therapy with prolonged high doses (eg, prednisone >20 mg daily) conferring the greatest risk. The incidence of osteonecrosis is higher among patients treated with prednisone in whom a cushingoid appearance develops. In contrast, most studies have found that the risk is low (<3%) among patients treated with doses of prednisone <15–20 mg daily. Osteonecrosis is a rare but recognized complication of Cushing syndrome due to pituitary or adrenal pathology.

Osteonecrosis develops in 3–30% of patients with systemic lupus erythematosus (SLE). SLE is an independent risk factor for osteonecrosis, but patients who have taken glucocorticoids, particularly doses of prednisone consistently >20 mg daily, are at greatest risk. Osteonecrosis can develop in SLE patients within a relatively short time following the initiation of glucocorticoid therapy. A decrease in bone mineral density within the first year of glucocorticoid initiation may be a predictor of osteonecrosis. Risk factors for the development of osteonecrosis in SLE include use of cytotoxic drugs, black race, Raynaud phenomenon, antiphospholipid antibodies, and hyperlipidemia.

Osteonecrosis affects 4–25% of patients following renal transplantation and, in this setting, is often multifocal. The risk decreases following the introduction of cyclosporine, tacrolimus, and mycophenolate mofetil and consequent reduction in glucocorticoid dose. Apart from glucocorticoid dose, risk factors for osteonecrosis include acute rejection, delayed graft function, preexisting hyperparathyroidism, and osteopenia. Osteonecrosis occurs in other transplantation settings including hematopoietic transplantation where the sex of donor and recipient affects risk (female donor to female recipient carries the highest risk).

Excessive alcohol use and the development of osteonecrosis have been linked for decades. An elevated risk for regular drinkers and a clear dose-response relationship have been noted.

Osteonecrosis develops in about 50% of patients with sickle cell disease by age 35, likely due to the combined effects of sickled red blood cells and bone marrow hyperplasia. Concomitant α-thalassemia increases the risk, while elevated hemoglobin F appears to be protective.

Gaucher disease is an autosomal recessive disorder of glucocerebroside metabolism that leads to the accumulation of cerebroside-filled cells within the bone marrow. This may result in compression of the vasculature and subsequent osteonecrosis, which has been reported in 60% of patients with Gaucher disease.

In dysbaric syndromes such as caisson disease and diver’s disease (“the bends”), decompression causes the formation of intravascular nitrogen bubbles that can occlude arterioles. Osteonecrosis can develop years after the exposure and is often multifocal. The pressure and number of decompressions are important risk factors.

Inherited thrombophilia

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