The diagnosis is avascular necrosis (AVN)or osteonecrosis of the hip. Although radiographs were previously used to evaluate for avascular necrosis, they only detect the later stages. When patients are clinically suspected of having AVN, MRI can show edema in the affected bone before trabecular collapse occurs and therefore should be performed when the diagnosis is clinically suspected. Radiography only detects later findings: (1) osteopenbia, cystic changes, bone sclerosis followed by the crescent sign and subchondral collapse without flattening of the affected bone. With trabecular bone collapse, there is flattening of the bone on radiographs. The most severe changes are those of secondary osteoarthritis with subchondral sclerosis, joint space narrowing, and osteophyte formation.

The causes of avascular necrosis are multiple including fracture, corticosteroids, thrombosis and embolism, vasculitis, increased intraosseous pressure with vascular compression, and venous hypertension, sickle cell disease, pancreatitis, alcoholism, tumors, pregnancy, and, in this case, radiation therapy causing vascular injury and ischemia(1). This patient received radiation
therapy for lymphoma. AVN may also be idiopathic, most commonly occurring in the 40-to-50-year-old man and is usually bilateral.(2)
Patients with AVN usually present with pain with exercise, but, with progression, pain may occur at rest. The course of the disease process is variable, but once there is subchondral collapse and joint space narrowing, the progression to osteoarthritis is usually slowly progressive. The disease can be divided into four stages based on symptoms, roentgenogram, bone scan results, and pathology results.(2). Symptoms may not correspond to the radiographic findings, and some patients with stage II disease have had spontaneous remission.(2)

Once early AVN is detected, conservative treatment with rest and crutches may provide some improvement. Other therapeutic approaches include: core decompression, bone grafting, vascularized fibular grafting, and transtrochanteric rotational osteotomy with variable results. With development of osteoarthritis, patients may have arthroplasty for relief of pain.