Purpose of the study: The anterior rim of the arthroplasty cup can overhang the bone in certain situations: oversized cup, insufficient anteversion, insufficient ace-tabular reaming, cylindrospherical reaming overriding the acetabular opening. The straight or concave shape of the anterior wall of the acetabulum also affects prosthetic overhang. The purpose of this anatomic study was to use a navigation system to quantify, in vitro, the height of the iliopubic psoas notch.

Material and methods: Sixty-eight acetabuli from 34 cadaver pelvi free of osteoarthritis (13 male and 21 female) were analyzed using the Stryker™ hip navigation system. Morphological data were collected for mathematical processing which defined the diameter and the center of the articular surface.

Results: Considerable intra- and inter-individual differences in the shape of the acetabular rim were noted and quantified, particularly concerning the psoas notch. When the lateral view of the acetabular rim is projected onto a plane it produces a succession of three summits and three valleys explaining the difficulty encountered in obtaining a precise mean plane for the acetabular opening.

Discussion: More or less pronounced protrusion of the cup could explain potentially painful anterior impingement of the psoas, especially for certain types of acetabular morphology.