Investigation into the affect of cementing techniques on load transfer in the resurfaced femoral head: a multi-femur finite element analysis.

BACKGROUND Femoral head resurfacing is a popular procedure for younger active hip replacement patients. Two major cementing techniques are used in femoral component fixation; producing varying cement mantle thicknesses. Each technique has benefits, but it is not known if cement mantle thickness is detrimental to load transfer within the proximal femur. METHODS This study uses computer tomography based finite element analysis to determine the effect of cement mantle thickness on strain in the resurfaced femoral head. A group of 16 femurs were investigated to take into account inter-patient variation; a factor often over-looked in such studies. FINDINGS Results showed strain in the proximal femoral head to decrease with increasing cement thickness, with a slight increase in strain in the posterior-superior neck. Cementing of the implant guide-pin produced marked reductions in strain in the head and neck except for the posterior-inferior neck; where it increased slightly. INTERPRETATION The study concluded that a thicker cement mantle increases strain shielding within the superior resurfaced femoral head; although short to medium term clinical trials do not suggest these factors to be of much concern. The analysis also found strain to increase around the inferior head-neck junction with a thinner mantle. Cementing the guide pin resulted in increased strain shielding whilst simultaneously shifting peak loads distally along the femoral neck. This work found that modelling a group of femurs was a useful tool for better interpreting the loading in the resurfaced femur.