Abstract
Introduction: It has been suggested that notching of the femoral neck during hip resurfacing weakens the proximal femur and predisposes to femoral neck fracture. We aimed to examine the effect of neck notching during hip resurfacing on the strength of the proximal femur.
Methods: 3rd generation composite femurs that have been shown to replicate the biomechanical properties of human bone were utilised. The bone was secured in a position of single leg stance and tested with an Instron mechanical tester. Imageless computer navigation was used to position the initial guide wire during head preparation. Six specimens were prepared without a superior notch being made in the neck of the femur, six were prepared in an inferiorly translated position to cause a 2mm notch in the superior femoral neck and six were prepared with a 5mm notch. The femoral component was then cemented in place. All specimens had radiographs taken to ensure that the stem shaft angle was kept constant. The specimens were then loaded to failure in the axial direction.
Results: The 2mm notched group (mean load to failure 4034N) were significantly weaker than the un-notched group (mean load to failure 5302N) when tested to failure (p=0.017). The 5mm notched group (mean load to failure 3121N) were also significantly weaker than the un-notched group (p=0.0003) and the 2mm notched group (p=0.046). All fractures initiated at the superior aspect of the neck, at the component bone interface. All components were positioned in the same coronal alignment +/−2 degrees.
Discussion: A superior notch of 2mm in the femoral neck weakens the proximal femur by 24% and a 5mm notch weakens it by 41%. This study provides biomechanical evidence that notching of the femoral neck may lead to an increased risk of femoral neck fracture following hip resurfacing.
Correspondence should be addressed to The Secretary, BHS, c/o BOA, The Royal College of Surgeons, 35–43 Lincoln’s Inn Fields, London WC2A 3PE.
