[Protrusio acetabuli. An update on the primary and secondary acetabular protrusion].

Acetabular protrusion refers to intrapelvic displacement of the medial wall of the acetabulum and is defined as inward movement of the acetabular line so that the distance between this line and the laterally located ilioischial line is 3 mm or more in adult men and 6 mm or more in adult women. As discussed in this article, acetabular protrusion may be found in many bone disorders such as degenerative joint disease, Paget's disease, rheumatoid arthritis, ankylosing spondylitis, osteomalacia, Marfan's disease and as an effect of irradiation. Protrusio acetabuli appearing in absence of any recognizable cause is termed primary acetabular protrusion or Otto pelvis. Primary acetabular protrusion usually affects both hips in young to middle aged women with a history of diminished abduction, rotation and hip pain since puberty. Radiographically one notes a bilateral axial migration of the femoral head without joint space loss and with moderate degenerative changes.