Healthy middle-aged Asian and Caucasian populations present with large intra- and inter-individual variations of lower limb torsion

Abstract

Purpose There is a lack of standardization in the measurement of lower limb torsional alignment. Normal values published in the literature are inconsistent. A 3D-CT-scan-based method was used in a healthy population to define the femoral neck version (FNV) and the tibial torsion (TT) and their relationship with demographic parameters. The study objectives were (1) to define normal values of lower limb torsional alignment, (2) to estimate inter- and intra-individual variations of torsional deformity of healthy individuals' lower limbs. The hypothesis was that FNV and TT values would be influenced by patient characteristics such as gender, age, and ethnicity, and would have low side-to-side asymmetry. Methods Torsional landmarks of the lower limbs from 191 healthy subjects were automatically calculated with a 3D CT-scan-based program. The FNV was defined by the angle between the femoral neck axis and the femoral posterior condylar line. The TT angle was considered between the tibial plateau axis and the axis of the ankle. For the former, two alternatives were considered: the line connecting the more medial and lateral point of the medial and lateral plateau, respectively (method 1TT1), or the line connecting the two more posterior points of the medial et lateral plateau (method 2TT2). The ankle axis was defined as the line connecting the medial and lateral malleoli. These reference lines were automatically calculated. Age, gender, ethnic group, and BMI were recorded for every subject. Apvalue < 0.05 was considered as statistically significant. Results Overall, the mean FNV was 15.3 +/- 9.5 degrees and the mean TT was 31.6 +/- 6.3 degrees. Female hips were more anteverted than male hips. Caucasians had less anteverted hips than Asians, but more externally rotated tibias. Age and BMI were not correlated with any anatomical parameter. A substantial side-to-side asymmetry was found for FNV {[}absolute difference (AD) = 6.3 degreespercentage of asymmetry (\%As) = 47\%], TT1 (AD = 3 degrees\%As = 12\%), and TT2 (AD = 4.9 degrees\%As = 9\%) (p = 0.008). Conclusion The findings showed that lower limb torsional parameters were highly variable from patient to patient and from one leg to the other for the same patient. The understanding of normal values concerning femoral version and external tibial torsion in the present healthy population will help surgeons to define pathological values of FNV and TT, as well as corrections to perform in case of torsional deformities.