Abstract
Acetabular protrusio is defined radiographically as migration of the femoral head medial to Kohler's line (a line from the lateral border of the obturator foramen to the medial border of the sciatic notch). Protrusio can develop in association with metabolic bone diseases such as osteogenesis imperfecta, Marfan's Syndrome, and Paget's disease, inflammatory arthritis or osteoarthritis, tumors, or result from prior trauma. Acetabular protrusio can cause limited hip motion due to impingement of the femoral neck against the acetabular rim. When protrusio develops in association with osteoarthritis, coxa vara is often also present.
Surgical treatment of acetabular protrusio during total hip arthroplasty should lateralise the center of the hip to its anatomic position. This typically can be achieved with use of a larger, slightly oversized, rim fit cementless acetabular component and medial morselised femoral head bone autograft. In cases with more severe deformity, a reconstruction cage may be required. Alternatively a medialised acetabular shell can be used with a lateralised liner. If coxa vara is also present, standard femoral component position (approximately 1cm above the lesser trochanter) can result in an increase in leg length. Careful pre-operative templating should be performed and may require more distal placement of the femoral component to avoid overlengthening the limb.
