A Biomechanical Study of Femoral Neck Notching Using The Birmingham Hip Resurfacing

"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: A three dimensional femoral model was used and molded with a femoral component constructed from the dimensions of a Birmingham Hip Resurfacing. Multiple constructs were made with the component inferiorly translated in order to cause a notch in the superior femoral neck.

The component angulation was kept constant. Once constructed the model was imported into the Ansys finite element model software for analysis. Elements within the femoral model were assigned different material properties depending on cortical and cancellous bone distributions. Von Misses stresses were evaluated near the notches and compared in each of the cases.

Results: In the un-notched case the maximum Von Mises stress was only 40MPa. However, with the formation of a 1mm notch the stress rose to 144MPa and in the 4 mm notch the stress increased to 423MPa. These values demonstrated that a 1mm notch increased the maximum stress by 361% while a 4mm notch increased the maximum stress by 1061%.

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