# Individual Bilateral Difference of Femur, Tibia, and Leg Rotation: A Clinical Study of 141 Healthy Japanese Individuals Using Computed Tomography

## TL;DR

This study measured natural rotation differences in femur and tibia bones among healthy Japanese individuals using CT scans to inform surgical practices.

## Contribution

The study provides population-specific data on bilateral femur and tibia rotation differences in Japanese individuals using CT scans.

## Key findings

- Mean absolute bilateral difference in femur rotation was 6.5° with 95% within 15°.
- Right tibia showed higher external rotation (3.3°) compared to the left side.
- Rotation differences between men and women were significant, but absolute and relative differences were not.

## Abstract

Background

The malrotation of a femur and tibial fracture after surgery has been described in many articles. However, these studies have not considered individual bilateral differences (IBDs). The IBD of femur and tibial rotation has been identified via computed tomography (CT) in recent American studies. The IBD in rotation should be considered during femur and tibial surgery. However, IBDs in femur and tibial rotation remain unknown in the Japanese population. This study aimed to evaluate the rotation of the femur, knee, tibia, and leg, sex differences, and IBD in rotation among Japanese individuals with healthy bones by using CT analysis.

Materials and methods

In total,141 patients who underwent CT angiography or venography were included (70 men, 71 women; mean age, 44.7 years). The bilateral axial femur, knee, tibia, and leg rotation alignment were independently measured. The distribution, sex, and IBD were analyzed. The IBD in rotation had two statistical factors: absolute bilateral difference (ABD) and relative bilateral difference (RBD).

Results

The mean ABD of femur rotation was 6.5°, and the distribution of ABD of femur rotation ≤15° was 95%. The mean ABD of tibia rotation was 5.1°, and the distribution of ABD of tibia rotation ≤10° was 89%. The RBD of femur rotation was not significantly different between the right and left sides. The RBD of tibia rotation showed a higher mean external rotation of 3.3° on the right side (<0.001). The Pearson correlation coefficients of the femur, knee, tibia, and leg rotation between the right and left sides were high (r= 0.702-0.81; all, p<0.001). All elements of rotation showed significant differences between men and women, whereas the ABD and RBD of all elements showed no significant difference.

Conclusion

The distributions of ABD in femur and tibia rotation supported the previous definition of an acceptable rotation difference between the normal and fractured femur and tibia of ≤15°and ≤10°, respectively. The possibility of higher external rotation on the right side needs to be taken into account during tibial surgery.