Factors that influence femoral neck length. Analysis of 1543 patients with advanced osteoarthritis of the hip.
There is little known about the relationship between patient characteristic and the variance in geometrical properties of the femoral neck. The length of the femoral neck is relevant when considering a femoral neck preserving hip replacement. Based on surgical experience we hypothesised that femoral neck length (FNL) decreased with age. We investigated whether certain patient characteristics were related to FNL and the femoral head diameter/FNL ratio. The femoral neck length of 1543 patients with osteoarthritis grade 3 and 4 was measured on calibrated pelvic radiographs. Increasing age and height were associated positively, while increasing CCD angle and femoral head diameter were associated negatively with femoral neck length. Female gender and height were associated negatively and CCD angle positively with the femoral head diameter/FNL ratio. The FNL in 10 year older individuals was on average 0.2 mm (1%) longer. Moreover, every 10 extra degrees in CCD coincided with a neck length decrease of 1.5 mm (8%) in our population. It seems justified to conclude that age is not a clinical relevant factor in the indication for femoral neck preserving hip arthroplasty. In this respect, CCD angle seems the most clinical relevant factor. Severe valgus angled hips are not a very suitable indication for femoral neck preserving prosthesis.