Kinematics of the normal arch of the foot and ankle under physiologic loading.

We studied 15 cadaver feet to determine three-dimensional motion of selected tarsal bones under axial loading at three different loading levels. We determined the motion of individual joints and also the rotation of the tarsal bones in relation to the tibia. Joint rotations increased consistently with higher loads. The naviculartalar joint had the greatest total screw axis rotation, which averaged 9.4 degrees +/- 2.2 degrees at 667 N of load, followed by the first metatarsal-navicular (mean, 7.2 degrees +/- 1.5 degrees), talartibial (mean, 5.2 degrees +/- 1.6 degrees), and calcaneal-talar (mean, 4.4 degrees +/- 1.7 degrees) joints. The observed changes indicate the need for assessment of foot and ankle alignment clinically and radiologically while the patient is weightbearing.