Subtalar joint kinematics defined by a rotational axis translating along the posterior talocalcaneal facet

The subtalar joint is essential for the normal function of the human foot during bipedal walking, with its kinematics being pivotal for understanding foot biomechanics, disorders, and evolution. Traditionally, the helical axis representation has been used to assess subtalar joint movement, assuming translational motion along the rotational axis. However, recent observations challenge this assumption, revealing predominantly mediolateral translation during walking. To address this discrepancy, we propose a novel method that combines a rotational axis representation with a translational axis aligned parallel to the cylindrical axis of the subtalar joint's posterior facet. Utilizing human cadaveric lower legs, we quantified subtalar joint motion through CT scan analysis. Comparative evaluations between the conventional helical axis representation and the newly proposed cylindrical axis-based representation revealed a closer correspondence between calcaneus movement and the cylindrical axis, emphasizing the pivotal role of posterior facet morphology in subtalar joint kinematics. This innovative approach provides a more intuitive and clinically useful depiction of subtalar joint biomechanics, potentially leading to deeper insights into fundamental biomechanics and function of the human foot, and improved clinical assessment and treatment strategies for subtalar joint-related pathologies.