Lateral direction of penetration into acetabular sockets using a 32 mm diameter femoral head

A cohort of 35 explanted acetabular sockets was examined to ascertain the direction of penetration. The penetration relative to the open face of the socket was measured using the shadowgraph method and the corresponding anatomical direction was then deduced using anterior-posterior radiographs. A median anatomical penetration direction of 17.5° lateral to the sagittal plane was found (range 27° medial to 44° lateral). These observations confound explanation through analysis of the motion and loading of the hip joint.