Calcar unloading after hip replacement. A cadaver study of femoral stem designs.

The load transfer from the pelvis to the femur in extension and 45 degrees of flexion was examined in normal hips and hips replaced with 11 different prostheses. The cadaver specimens were mounted in a jig and the load patterns recorded by strain gauges attached to critical points determined in a pilot study, with the aid of a photoelastic coating. All the prostheses except an "isoelastic" model showed marked reduction of strain in the calcar area compared with the normal femur. A collar increased the strain to about 40 per cent of normal. No significant difference was noted between curved and straight stems. There were no major differences between the prostheses on loading in flexion.