IS STEM LENGTH IMPORTANT IN UNCEMENTED ENDOPROSTHESES

In an uncemented total hip replacement where the femoral stem is thinn er than the medullary canal it may be hypothesized that the distal por tion of the stem has no mechanical function. In this study an uncement ed total hip replacement has been modelled mathematically using finite element analysis and mechanical tests of a similar system have been c arried out loading implants in cadaveric proximal femora. Two implants have been tested mechanically; one with a full length stem and the se cond with the stem shortened, but three implants have been modelled wi th an additional intermediate length stem analysed. Additionally the f inite element analysis has been done with a high neck resection and a standard level resection. The finite element model showed that the ful l length sta produced lower interface contact stress levels under the proximal neck, particularly when the neck was resected, and this was b orne out by the mechanical testing.