Musculoskeletal · Orthopedics
The facts most likely to be tested
Chronic corticosteroid use and excessive alcohol consumption are the two most common non-traumatic risk factors for avascular necrosis (AVN).
Patients typically present with insidious onset of groin pain that is exacerbated by weight-bearing activities and internal rotation of the hip.
MRI of the hip is the gold standard diagnostic modality due to its superior sensitivity in detecting early-stage disease before radiographic changes occur.
Early-stage radiographs often appear normal, but advanced disease demonstrates the crescent sign, representing a subchondral fracture of the femoral head.
Sickle cell disease and other hemoglobinopathies cause AVN through microvascular occlusion and subsequent ischemic bone necrosis.
Legg-Calvé-Perthes disease is the pediatric equivalent of AVN, characterized by idiopathic osteonecrosis of the femoral head in children aged 4 to 10.
Definitive management for advanced disease with femoral head collapse is total hip arthroplasty to restore joint function and alleviate pain.
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A 42-year-old male presents with a 3-month history of progressive right groin pain that worsens with walking. He has a significant medical history of systemic lupus erythematosus managed with long-term high-dose prednisone therapy. Physical examination reveals limited internal rotation and abduction of the right hip. Radiographs of the hip show no acute fracture or joint space narrowing. The patient is currently unable to bear weight comfortably on the affected side.
What is the most appropriate next step in the diagnostic evaluation?
MRI of the hip
The patient's history of chronic corticosteroid use and clinical presentation are classic for AVN; MRI is the most sensitive test to confirm the diagnosis when initial radiographs are negative.
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Etiology / Epidemiology
Common in chronic corticosteroid use and alcoholism. Often presents in patients aged 30-50.
Clinical Manifestations
Insidious onset of groin pain exacerbated by weight-bearing. Crescent sign on imaging.
Diagnosis
MRI is the gold standard for early detection. Plain radiographs are often normal in early stages.
Treatment
Core decompression for early stages; total hip arthroplasty for advanced collapse.
Prognosis
High risk of femoral head collapse and secondary osteoarthritis requiring surgical intervention.
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Epidemiology & Etiology
Primary risk factors include prolonged corticosteroid use, excessive alcohol intake, and trauma (femoral neck fractures). Other associations include sickle cell disease, Gaucher disease, and systemic lupus erythematosus. It is most prevalent in the 30-50 age demographic.
Pertinent Anatomy
The femoral head relies on the medial circumflex femoral artery. Disruption of this blood supply leads to osteocyte death and subsequent structural failure of the subchondral bone.
Pathophysiology
Ischemia leads to osteocyte necrosis and bone marrow death. The repair process is insufficient, resulting in subchondral bone resorption and structural weakening. Eventually, the articular cartilage collapses, leading to secondary osteoarthritis.
Clinical Manifestations
Patients present with groin pain that radiates to the thigh or knee. Pain is typically worse with weight-bearing and at night. Physical exam shows limited internal rotation and abduction. Red flag: sudden worsening of pain suggests femoral head collapse.
Diagnosis
MRI is the most sensitive test for early diagnosis. Plain radiographs may show the crescent sign (subchondral lucency) in later stages. Bone scintigraphy is an alternative if MRI is contraindicated.
Treatment
Early-stage management focuses on core decompression to reduce intraosseous pressure. Bisphosphonates may be used to delay collapse in early disease. Avoid weight-bearing during the acute phase. Advanced disease requires total hip arthroplasty.
Prognosis
Without intervention, the majority of patients progress to femoral head collapse within 2-3 years. Total hip arthroplasty is the definitive treatment for end-stage disease.
Differential Diagnosis
Septic arthritis: acute fever and elevated inflammatory markers
Osteoarthritis: older age and joint space narrowing on X-ray
Transient osteoporosis of the hip: self-limiting, usually in middle-aged men
Femoral neck fracture: acute trauma history
Referred lumbar radiculopathy: pain follows a dermatomal distribution