In patients where the proximal femur shows gross deformity due
to degenerative changes or fracture, the contralateral femur is
often used to perform preoperative templating for hip arthroplasty.
However, femurs may not be symmetrical: the aim of this study was
to determine the degree of variation between hips in healthy individuals and
to determine whether it is affected by demographic parameters. CT-scan based modelling was used to examine the pelvis and bilateral
femurs of 345 patients (211 males, 134 women; mean age 62 years
(standard deviation (Aims
Materials and Methods
The contralateral femur is frequently used for preoperative templating of total hip arthroplasty assuming femoral symmetry. We aimed to define the degree of asymmetry between left and right proximal femurs and whether if affected by demographics parameters. A CT-scan based modeling and analytics system of 346 CT-scans was used for this study, including pelvis and bilateral femora from 211 men and 135 women (mean age 61 ±16 years, mean BMI 26± 5 kg/m2). The femoral neck shaft angle (NSA), femoral offset (FO), femoral neck version (FNV), femoral length (FL), canal flare index (CFI) and femoral head diameter (FHD) were calculated for each patient. We then, analyzed symmetry based on absolute differences(AD) and percentage of asymmetry(%AS). An asymmetry >2% was found for NSA (mean AD=2.9°; mean %AS=2.3; p=0.03), FO (AD=3.8mm; %AS=9.1; p=0.01), FNV (AD=5.1°; %AS=46.7; p=0.001) and CFI (AD=0.2mm; %AS=5.4; p=0.7). Percentage of asymmetry was <2% for FL (AD=3.6mm; %AS=0.8; p=0.7) and FHD (AD=0.3mm; %AS=1.2; p=0.8). No correlation and predictive value was found between either AD or %AS and age, ethnicity, gender, height, weight or BMI. Our data support assumptions of substantial asymmetry of the proximal femur which is not affected by demographics or proximal femoral size. Clinical relevance: Upper femurs are not symmetric. Preoperative planning on contralateral femur might be affected this geometrical bias.
