Avascular Necrosis of the Femoral Head: Causes and Management
Causes and Risk Factors
AVN of the femoral head results from inadequate vascular supply leading to bone death, with multiple identifiable risk factors that should be systematically evaluated. 1
Common etiologies include:
- Corticosteroid therapy (most common cause in nontraumatic cases, accounting for 72% of cases) 2, 3
- Alcohol use 2, 1
- Trauma (displaced subcapital or transcervical fractures, particularly in elderly patients) 4
- HIV infection 2, 1
- Hematologic disorders including lymphoma, leukemia, blood dyscrasias, and idiopathic thrombocytopenic purpura 2, 3
- Chemotherapy and radiation therapy 2, 1
- Gaucher disease and Caisson disease 2
- Idiopathic causes (12% of cases) 3
Critical clinical pitfall: Nontraumatic AVN is bilateral in 70-80% of cases, requiring evaluation of both hips even when symptoms are unilateral 2, 1. Additionally, multifocal osteonecrosis occurs frequently, affecting the knee (44%), ankle (17%), and shoulder (15%) in patients with femoral head involvement 2, 1.
Prognostic Factors
The necrotic volume is the single most critical prognostic indicator:
- Lesions involving <30% of the femoral head progress to collapse in <5% of cases 2, 1, 5
- Lesions involving >30% of the femoral head progress to collapse in 46-83% of cases 2, 1, 5
Additional poor prognostic factors include:
- Patient age >40 years 2, 1
- BMI >24 kg/m² 2, 1
- Presence of joint effusion 2, 1
- Increased bone marrow edema surrounding the necrotic focus 2, 1
Management Algorithm
Early-Stage Disease (Ficat Stage I, IIA, IIB - Before Articular Collapse)
Core decompression is the primary surgical intervention for early-stage disease, as it aims to prevent articular collapse and delay joint replacement. 1, 5
Noninvasive therapies can be attempted first, though supporting data remains limited 2, 1:
- Statins
- Bisphosphonates
- Anticoagulants
- Extracorporeal shock wave therapy
- Hyperbaric oxygen
Core decompression techniques:
Postoperative management after core decompression:
- Protected weight-bearing to prevent fracture 5
- Regular radiographic follow-up to monitor for disease progression or femoral head collapse 5
Important caveat: The overall efficacy of core decompression at preventing eventual articular collapse remains controversial, though earlier intervention yields better results 2, 4.
Late-Stage Disease (Ficat Stage III, IV - With Articular Collapse)
For late-stage disease with articular collapse, arthroplasty is the definitive treatment. 1, 5
Surgical options:
- Resurfacing hemiarthroplasty for late-stage osteonecrosis with articular collapse but preserved acetabulum 2, 1
- Total hip arthroplasty for severe secondary osteoarthritis involving both femoral head and acetabulum 2, 1, 4
Clinical context: AVN of the femoral head accounts for 10% of all total hip replacements performed in the United States 2. In elderly patients with traumatic AVN from displaced fractures, attempts to preserve the femoral head are generally not indicated, and primary arthroplasty is the treatment of choice 4.
Diagnostic Approach
Early diagnosis is crucial to prevent articular collapse and preserve treatment options. 1, 4
Imaging sequence:
- MRI is the gold standard for early detection before radiographic changes appear 2
- CT with IV contrast can retrospectively identify cases and is essential for surgical planning, showing precise location and extent of necrotic lesion 2, 5
- Plain radiographs are less sensitive for early disease but useful for staging 2
Common diagnostic pitfall: Many cases are asymptomatic and vastly underreported, particularly metadiaphyseal cases that can be retrospectively visualized on CT scans performed for other clinical purposes 2.