Strain Gauge and Photoelastic Evaluation of the Load Transfer in the Pelvis in Total Hip Replacement: The Effect of the Position of the Axis of Rotation

Aseptic loosening of the acetabular component is the principal long-term complication in total hip replacement. Radiographic evidence suggests a higher incidence of loosening with medialization of the axis of rotation of the acetabular cup. A simplified two-dimensional photoelastic investigation of the load transfer in the pelvis demonstrates that the stress distribution is substantially changed when this axis of rotation is medialized. Strain gauge measurements on three dry hemi-pelvic bones confirm this effect. It is postulated that the redistribution of load resulting from medialization may result in inadequate skeletal support for the acetabular component predisposing to loosening.