Bilateral Symmetry, Sex Differences, and Primary Shape Factors in Ankle and Hindfoot Bone Morphology

Background: Ankle injuries and joint degeneration may be related to ankle bone morphology. Little data exist to characterize healthy hindfoot bone morphology. The purpose of this study was to characterize side-to-side symmetry and sex differences in ankle and hindfoot bone morphology, and to identify the primary shape factors that differentiate ankle and hindfoot bone morphology among individuals.

Methods: Computed tomography was used to create 3D surface models of the distal tibia, talus, and calcaneus for 40 ankle and hindfoot bones from 20 healthy individuals. Morphologic differences between left and right bones of the same individual and between males and females were determined. Statistical shape modeling was performed to identify primary shape variations among individuals.

Results: Side-to-side differences in bone morphology averaged 0.79 mm or less. The average distal tibia in males was larger overall than in females. No significant sex difference was noted in the tali. The average female calcaneus was longer and thinner than the average male calcaneus. Variability in ankle and hindfoot bone morphology is primarily associated with articulating surface shape, overall length and width, and tendon/ligament attachment points.

Conclusion: In general, the contralateral ankle can serve as an accurate guide for operative restoration of native ankle morphology; however, specific regions demonstrate higher asymmetry.

Clinical Relevance: Knowledge of regions of high and low bilateral symmetry can improve hindfoot and ankle reconstruction. Design of ankle prostheses can be improved by accounting for differences in bone morphology associated with sex and shape differences among individuals.