Effects of positioning and notching of resurfaced femurs on femoral neck strength: a biomechanical test.

PURPOSE To assess the effects of positioning and notching of resurfaced femurs on the mechanical strength of third-generation saw bone (TGSB) femurs using an in vitro analogue bone model. METHODS 30 TGSB femurs were equally divided into 6 resurfaced femur groups (intact, anatomic, varus, valgus, anatomically notched, and valgus notched) for testing the load to failure, stiffness, and total energy. RESULTS Compared to the intact femurs, the load to failure in all resurfaced femurs was significantly decreased by 29 to 57%. Among the resurfaced femurs, valgus and anatomic femurs had the highest load to failure, followed by valgus notched, varus, and anatomically notched femurs. Notching weakened the construct by a further 24 to 30%. CONCLUSION To minimise the risk of femoral neck fracture, resurfaced femoral heads should be placed in an anatomic or valgus orientation, and the superior cortex of the femoral neck should remain intact.