Femoral neck fracture following hip resurfacing: the effect of alignment of the femoral component.

A total of 20 pairs of fresh-frozen cadaver femurs were assigned to four alignment groups consisting of relative varus (10 degrees and 20 degrees) and relative valgus (10 degrees and 20 degrees), 75 composite femurs of two neck geometries were also used. In both the cadaver and the composite femurs, placing the component in 20 degrees of valgus resulted in a significant increase in load to failure. Placing the component in 10 degrees of valgus had no appreciable effect on increasing the load to failure except in the composite femurs with varus native femoral necks. Specimens in 10 degrees of varus were significantly weaker than the neutrally-aligned specimens. The results suggest that retention of the intact proximal femoral strength occurs at an implant angulation of > or = 142 degrees . However, the benefit of extreme valgus alignment may be outweighed in clinical practice by the risk of superior femoral neck notching, which was avoided in this study.