Sex differences in femoral deformity determined using three-dimensional assessment for osteoarthritic knees

Purpose To characterize femoral deformities and determine sex differences in varus knee osteoarthritis (OA), femoral morphology and limb alignment were evaluated by using three-dimensional (3D) assessment, comparing healthy, elderly volunteers with osteoarthritic knees. Methods A total of 178 lower limbs of 169 subjects with knee osteoarthritis (136 women, 33 men; mean age 74.9 ± 5.2 years) and 80 lower limbs of 45 healthy, elderly subjects (24 women, 21 men; mean age 65 ± 4.9 years) were examined. A 3D extremity alignment assessment system was used to examine the subjects under weight-bearing conditions on biplanar long-leg radiographs using a 3D-to-2D image registration technique. The evaluation parameters were (1) femoral bowing in the coronal plane, (2) femoral bowing in the sagittal plane, (3) femoral neck anteversion, (4) hip–knee–ankle angle, and (5) femoral torsion. Results Higher femoral lateral bowing and slightly higher femoral internal torsion in the proximal diaphysis were observed in women with OA compared with healthy subjects. No difference in the higher varus malalignment, no alteration in the femoral anterior bowing, and no difference in the lower femoral neck anteversion were found between men and women when comparing healthy and OA subjects. Conclusions The higher femoral lateral bowing and slightly higher femoral internal torsion in the proximal diaphysis in women are possibly a structural adaptation to mechanical use. The clinical significance is that the femoral deformities and the sex differences in knee OA have the potential to improve the understanding of the aetiology of primary varus knee OA. Level of evidence IV.