A pelvic radiograph done for other reasons shows increased sclerosis of the right femoral head with normal appearance of the right hip joint.
CT scan performed later confirms the finding of avascular necrosis (areas of mixed lysis and sclerosis in the femoral head with normal hip joint).
- Relatively common disease, femoral head most common site
- Predisposing factors: hip dislocation, femoral neck fracture, corticosteroid usage, collagen vascular disease, hemoglobinopathies
- Often affecting young adults
- Early diagnosis is important to establish AVN as the cause of hip pain (excluding infection, neoplasm, fracture, or tendon tear) and to stage AVN for treatment
- Radiograph most widely used as initial study. Both AP and frogleg views should be obtained to detect subchondral fracture or cortical depression. It may be normal, abnormal or nonspecific.
- CT can be done to determine severity of secondary degenerative joint disease or extent of collapse of the femoral head (use for planning of either osteotomy or joint replacement)
- MRI is the most sensitive imaging method.
- Suspicious for AVN in a high-risk patient with hip pain -> AP and frogleg lateral radiograph of the symptomatic hip
- If radiograph is definite for AVN -> MRI to look for AVN in the opposite side IFknowledge of asymptomatic AVN in the opposite side is clinically important
- If radiograph is equivocal or normal -> MRI to confirm the diagnosis of AVN and to exclude other causes
- If MRI cannot be performed, a bone scan with SPECT imaging reasonable