Avascular necrosis (AVN) of the femoral head is a pathologic process that results from interruption of blood supply to the bone. AVN of the hip is poorly understood, but this process is the final common pathway of traumatic or nontraumatic factors that compromise the already precarious circulation of the femoral head. Femoral head ischemia results in the death of marrow and osteocytes and usually results in the collapse of the necrotic segment. (See also the Medscape Reference article Imaging in Avascular Necrosis of the Femoral Head, as well as Hip Arthroscopy in Staging Avascular Necrosis of the Femoral Head on Medscape News.)
Osteonecrosis of the femoral head was first described in 1738 by Munro. In approximately 1835, Cruveilhier depicted femoral head morphologic changes secondary to interruption of blood flow. Since 1962, when Mankin described 27 cases of AVN, the number of reported AVN cases has increased steadily. (See also the Medscape Reference article Hip Osteonecrosis.)
Early radiographic findings in femoral head AVN include femoral head lucency and subchondral sclerosis. With disease progression, subchondral collapse (ie, crescent sign) and femoral head flattening become evident radiographically. Joint space narrowing is the end result of untreated femoral head AVN.
Magnetic resonance imaging (MRI) is the study of choice in patients who demonstrate signs and symptoms that are suggestive of AVN but whose radiographs are normal.
Essentially, nonoperative treatment for symptomatic AVN of the hip yields unfavorable results. Small asymptomatic lesions do not warrant surgical intervention and are closely monitored with serial examination. If symptoms ensue, repeat imaging and surgical treatment are indicated.
Surgical treatment of AVN can be broadly categorized as either prophylactic measures (to retard progression) or reconstruction procedures (after femoral head collapse).
For excellent patient education resources, see eMedicineHealth’s patient education article Total Hip Replacement.