Protrusio acetabuli

 Protrusio. There is bilateral acetabular protrusio White arrows). The femoral head should not extend medial to a line drawn from the lateral aspect of the pelvis and the lateral aspect of the obturator foramen (blue line). The distance between the acetabulum and the ilioischial line (yellow arrow) should not be > 3mm in males and >6 mm in females.

Acetabular ProtrusioProtrusio Acetabuli General Considerations Intrapelvic displacement of the medial acetabular wall Most common cause is osteoarthritis Primary form – Otto pelvis Marked female to male predominance Usually occurs in young to middle-aged Bilateral in 1/3 to 2/3 of patients No underlying causative mechanism is demonstrated Secondary form Rheumatoid arthritis Paget disease Central fracture-dislocation Hip implants Marfan Syndrome Osteomalacia Clinical Findings May be asymptomatic, or have Limitation of motion Joint stiffness Pain Imaging Findings Bilateral axial migration of the femoral heads with or without moderate degenerative changes Distance between the acetabulum and the ilioischial line should be >3 mm in males and >6 mm in females in protrusio Femoral head should not project medial to a line joining the inner border of the pelvis and the lateral margin of the obturator foramen Complications Coxa vara and decreased femoral anteversion Treatment Depends on age and degree of degenerative changes Medial wall bone grafts Joint replacement surgery may be necessary