Effect of tibial coronal inclination on hindfoot kinematics: A biomechanical simulation study

Tibial coronal inclination is often recognized in everyday life, but the compensatory kinematic changes to maintain plantigrade of the hindfoot in response to tibial coronal inclination remain unclear. Lower legs and foot specimens obtained from seven human cadavers were loaded vertically with traction of Achilles' tendon in different tibial inclinations: 0° (neutral), 5°, and 10° medial inclination, and 5° and 10° lateral inclination. The orientations of the tibia, talus, and calcaneus were recorded under vertical load by a three-dimensional digitizing stylus. The angular changes of the talocrural and subtalar joints in the tibial inclinations from neutral were analyzed. The heights of the origins of the talus and calcaneus were also recorded. As the tibia was medially inclined from neutral, the talocrural joint was significantly more dorsiflexed. The subtalar joint was significantly more inverted, plantarflexed, and internally rotated. However, such significant changes in the joint angles were not observed when the tibia was laterally inclined. The height of the talus decreased as the tibia was medially inclined, but it was vice versa when laterally inclined. The compensatory motions of the hindfoot to tibial medial inclination involved coupled movement of both the talocrural and subtalar joints; such motions flatten the medial foot by decreasing the height of the talus. However, such compensatory capacities of the hindfoot to tibial lateral inclinations were limited. Tibial medial inclination under axial loading affects the kinematics of the hindfoot, and this is an important factor to consider in the treatment of flatfoot as well as foot orthotic/footwear intervention.