Diagnosing Avascular Necrosis of the Femoral Head

Initial Imaging Approach

• The American College of Radiology recommends starting with plain radiographs of the hip in two planes as the first-line imaging study for clinically suspected osteonecrosis, despite their limited sensitivity in early disease 1
• If radiographs are normal or show only suspicious findings in a patient with clinical suspicion for AVN, proceed immediately to MRI, as recommended by the American College of Radiology 1

MRI Without IV Contrast: The Gold Standard

• MRI without intravenous contrast is the most sensitive and specific imaging modality for diagnosing osteonecrosis, with sensitivity and specificity nearing 100%, according to the American College of Radiology 1
• A meta-analysis of 43 studies reported 93% sensitivity and 91% specificity for early detection of femoral head osteonecrosis, as cited by the American College of Radiology 1
• MRI characterizes the osteonecrosis, including location, volume (necrotic angle), and presence of associated bone marrow edema or joint effusion, as recommended by the American College of Radiology 1
• MRI detects asymptomatic disease in the contralateral hip, which is crucial since nontraumatic osteonecrosis is bilateral in 70-80% of cases, although this specific statistic is not directly cited, the importance of bilateral assessment is 1
• MRI differentiates AVN from mimics such as transient bone marrow edema syndrome and subchondral insufficiency fracture, as recommended by the American College of Radiology 1

Optimal MRI Protocol

• The American College of Radiology suggests that a coronal STIR sequence alone shows 100% sensitivity for detecting AVN 2
• Adding a coronal T1-weighted sequence increases confidence and specificity, as recommended by the American College of Radiology 2

Alternative Imaging Modalities: When and Why to Avoid

• CT without IV contrast is less sensitive than MRI and bone scintigraphy for detecting early osteonecrosis, according to the American College of Radiology 1
• CT is superior to MRI only for showing location and extent of articular collapse and osseous details of secondary osteoarthritis, as noted by the American College of Radiology 1
• Bone scintigraphy is not beneficial for characterization due to poor spatial resolution, low specificity, and inability to quantify necrotic lesion size, as stated by the American College of Radiology 1
• MRI with IV contrast is not necessary for diagnosis of osteonecrosis itself but can be useful in differentiating osteonecrosis from transient bone marrow edema syndrome or subchondral insufficiency fracture, as recommended by the American College of Radiology 1

Algorithmic Approach

• The American College of Radiology recommends obtaining plain radiographs first (AP and lateral hip views) 1
• If radiographs are negative or equivocal and clinical suspicion remains high, proceed directly to MRI without IV contrast, as recommended by the American College of Radiology 1
• If MRI is contraindicated, CT without contrast is an acceptable but less sensitive alternative, according to the American College of Radiology 1
• Once AVN is confirmed on MRI, measure necrotic angle and document risk factors for prognosis and treatment planning, although specific guidelines are not provided in the cited references, the importance of MRI in this context is 1
• If articular collapse is present on radiographs, either MRI or CT is appropriate for preoperative planning, with CT superior for depicting collapse extent, as noted by the American College of Radiology 1

Hip Osteonecrosis: Risk Factors, Symptoms, and Clinical Considerations

Risk Factors

• The American College of Radiology identifies corticosteroid therapy as one of the most common causes of hip osteonecrosis 3
• Chemotherapy is a risk factor for hip osteonecrosis 3
• Radiation therapy is a risk factor for hip osteonecrosis 3
• Alcohol consumption is a major risk factor for hip osteonecrosis 3
• HIV infection is a risk factor for hip osteonecrosis 3, 4
• Lymphoma/leukemia is a risk factor for hip osteonecrosis 3
• Gaucher disease is a risk factor for hip osteonecrosis 3
• Caisson disease (decompression sickness) is a risk factor for hip osteonecrosis 3
• Hemoglobinopathies are risk factors for hip osteonecrosis 4
• Hypercoagulability states are risk factors for hip osteonecrosis 4
• Hyperlipidemia is a risk factor for hip osteonecrosis 4
• Direct hip trauma or fracture is a risk factor for hip osteonecrosis 3

Prognostic Risk Factors

• Age >40 years worsens outcomes in hip osteonecrosis 5, 6
• BMI >24 kg/m² worsens outcomes in hip osteonecrosis 5, 6
• Joint effusion worsens outcomes in hip osteonecrosis 5, 6
• Increased bone marrow edema worsens outcomes in hip osteonecrosis 5, 6

Clinical Symptoms

• Hip pain is the cardinal symptom that prompts patients to seek medical attention for hip osteonecrosis 4
• The American College of Radiology emphasizes that early diagnosis is critical because symptoms indicate the disease process is already underway 3, 7
• Approximately 5% of HIV patients may have asymptomatic disease detected only on MRI 4

Critical Clinical Considerations

• Nontraumatic osteonecrosis is bilateral in 70-80% of cases, requiring evaluation of both hips even when symptoms are unilateral 5, 6
• The American College of Radiology emphasizes that early diagnosis is important to exclude other causes of pain and allow for possible early surgical prevention to prevent articular collapse and need for joint replacements 3, 7
• Lesions involving <30% of the femoral head have <5% progression to collapse, while lesions >30% have 46-83% risk of progression 5, 6

Osteonecrosis of the Femoral Head Diagnosis and Presentation

Clinical Presentation and Diagnosis

• The American College of Radiology suggests that osteonecrosis of the femoral head characteristically causes hip pain that increases with activity and weight-bearing, not pain that is relieved by activity 8, 9
• The described night pain is more consistent with inflammatory arthropathy, infection, or malignancy rather than osteonecrosis 8
• The American College of Radiology recommends plain radiographs as the initial imaging step for suspected osteonecrosis 10, 11
• MRI without IV contrast is the gold standard for definitive imaging with sensitivity and specificity approaching 100% 10, 11, 12, 13
• A meta-analysis showed 93% sensitivity and 91% specificity for early detection of femoral head osteonecrosis using MRI 11, 12

Alternative Diagnoses and Laboratory Studies

• Inflammatory arthritis should be considered as it typically improves with movement and worsens with rest 9
• Malignancy is a consideration due to unrelenting night pain being a red flag 11
• Transient bone marrow edema syndrome also causes activity-related pain worsening 11, 12, 13
• Laboratory tests may identify underlying risk factors but do not confirm the diagnosis of osteonecrosis 9
• No specific biomarker exists for osteonecrosis diagnosis 8, 9

Corticosteroid Dose, Cyclosporine Use, and Dialysis Duration as Risk Factors for Avascular Necrosis of the Femoral Head

High‑Dose Corticosteroid Therapy

• In patients receiving corticosteroid therapy, daily prednisolone doses of ≥30 mg markedly increase the risk of developing avascular necrosis of the femoral head, especially when the dose is escalated rapidly without prior tapering. 14

Cyclosporine A as a Steroid‑Sparing Agent

• Administration of Cyclosporine A may reduce the incidence of avascular necrosis by allowing lower cumulative corticosteroid doses, although the supporting studies have methodological limitations. 14

Prolonged Dialysis Prior to Renal Transplantation

• Individuals who undergo extended periods of dialysis before receiving a renal transplant have a higher probability of developing avascular necrosis of the femoral head. 14

Corticosteroid‑Related Risk and Management of Avascular Necrosis of the Hip

Risk Stratification Based on Corticosteroid Exposure

• High‑dose glucocorticoid therapy (e.g., daily prednisolone ≥ 30 mg) increases the risk of hip avascular necrosis by at least 1.5‑fold compared with low‑dose regimens. 15
• A meta‑analysis of studies comparing high‑ versus low‑dose corticosteroid regimens found a significantly higher incidence of avascular necrosis with high‑dose exposure (P < 0.001; odds ratio = 2.74), indicating strong evidence for a dose‑response relationship. 15

Modifiable Risk‑Factor Management

• When medically feasible, clinicians should discontinue or reduce the corticosteroid dose to lower the risk of progression or development of avascular necrosis. 15