Effects of coronally slotted femoral prostheses on cortical bone strain.

The photoelastic method was used to assess the effects on femoral cortical strain of total hip arthroplasty cementless femoral prostheses containing distal coronal slots. Eight cadaveric femurs were tested, although three were eliminated secondary to fractures. Loaded and unloaded cortical strains were determined at 72 points on the implanted femoral cortex and compared with the values obtained in the intact femur. Three different prostheses were sequentially implanted, in a random order, into each femur. The prostheses consisted of a standard solid stem, an identical stem with a coronal slot in its distal one fourth, and an identical stem with a coronal slot in its distal one half. The slotted stems did not enhance axial load transfer to the proximal medial femur but did result in increased proximal medial assembly strains and statistically significant (P < .05) decreased anterior and posterior assembly strains. The increased proximal medial assembly strains are hypothesized to enhance proximal medial femoral loading, while the decreased anterior and posterior assembly strains may minimize operative implantation fractures.