Hemispheric cups do not reproduce acetabular rim morphology

Background Iliopsoas impingement is a recurrent complication following THA, caused by muscle friction against a protrusive prosthetic cup.This study was designed to quantify the dimensional variations in acetabular rim proiles, with particular regard to the iliopubic valley, in order to suggest means to prevent iliopsoas impingement.

Material and methods 34 cadaver pelvises were analyzed using a hip navigation system.The morphometric data were processed to plot proiles of all acetabular rims with particular regard to the shape and depth of the psoas valley.

Results The acetabular rim is an asymmetric succession of 3 peaks and 3 troughs.The psoas valley is a salient feature in most pelvises and there is only a weak correlation between its depth (mean 3.8 mm, SD 2.0) and acetabular diameter, anteversion, or inclination.

Interpretation It would be dificult to obviate the anterior overlap of the acetabulum using a hemispheric cup, a fortiori in certain morphotypes, without compromising range of motion or risk of dislocation.The solution for prevention of iliopsoas impingement would be to adapt cup design to acetabular anatomy, which may require different implants for the right and left sides, and hence a doubled inventory.