In tuberculosis of the hip, the 'wandering acetabulum' deformity describes which radiological finding indicating advanced disease?
- A Protrusion of the acetabulum medially into the pelvis due to destruction of the acetabular floor, causing the femoral head to migrate medially ✓
- B Migration of the femoral head superolaterally out of the acetabulum due to capsular distension
- C Lateral displacement of the acetabulum due to growth plate destruction in children
- D Superior migration of the acetabulum due to pelvic obliquity from longstanding hip flexion contracture
Correct answer: A. Protrusion of the acetabulum medially into the pelvis due to destruction of the acetabular floor, causing the femoral head to migrate medially
Explanation
In advanced TB of the hip, destruction of the acetabular floor allows the femoral head — driven by muscle forces — to erode medially into the pelvis, producing 'protrusio acetabuli' or 'wandering acetabulum.' The acetabulum effectively 'wanders' medially due to bone loss, a sign of severe articular and periarticular disease. This is distinct from superior migration seen in osteoarthritis or the lateral subluxation of early septic arthritis. Radiologically it manifests as breaking of Kohler's line (medial wall of acetabulum projects medial to ilioischial line).
Reference: Maheshwari Essential Orthopaedics, 6th ed.
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