Foot kinematics as a function of ground orientation and weightbearing.

The foot is responsible for the bodyweight transfer to the ground, while adapting to different terrains and activities. Despite this fundamental role, the knowledge about the foot bone intrinsic kinematics is still limited. The aim of the study is to provide a quantitative and systematic description of the kinematics of all bones in the foot, considering the full range of dorsi/plantar flexion and pronation/supination of the foot, both in weightbearing and nonweightbearing conditions. Bone kinematics was accurately reconstructed for three specimens from a series of computed tomography scans taken in weightbearing configuration. The ground inclination was imposed through a set of wedges, varying the foot orientation both in the sagittal and coronal planes; the donor body-weight was applied or removed by a cable-rig. A total of 32 scans for each foot were acquired and segmented. Bone kinematics was expressed in terms of anatomical reference systems optimized for the foot kinematic description. Results agree with previous literature where available. However, our analysis reveals that bones such as calcaneus, navicular, intermediate cuneiform, fourth and fifth metatarsal move more during foot pronation than flexion. Weightbearing significantly increase the range of motion of almost all the bone. Cuneiform and metatarsal move more due to weightbearing than in response to ground inclination, showing their role in the load-acceptance phase. The data here reported represent a step toward a deeper understanding of the foot behavior, that may help in the definition of better treatment and medical devices, as well as new biomechanical model of the foot.