Shank rotation: A measure of rearfoot motion during normal walking.

Motion of the shank in the transverse plane is coupled with pronation and supination of the rearfoot, and so its motion relative to the foot can be used as an indicator of the pattern of motion in the rearfoot. Compared to the more commonly used assessment of motion in the frontal plane between the heel and the shank, motion of the shank in the transverse plane relative to the foot provides a more complete measure of the pattern of motion of the rearfoot because it reflects the motion in all three joints of the rearfoot (the ankle, subtalar joint and mid-tarsal joint) not solely the ankle and subtalar components. This work aimed to provide normative data for this alternative measure of rearfoot function. Data on angular displacement, angular velocity and angular acceleration were derived from motion-analysis conducted on 25 subjects. The results suggest a difference between the pattern of angular displacement indicated when motion of the shank relative to the foot is examined and the pattern of angular displacement indicated when motion in the frontal plane between the shank and heel is examined. Specifically, the former suggests that resupination of the rearfoot after rearfoot pronation during the initial period of gait, starts at the beginning of mid-stance, while the latter suggests resupination beginning in late mid-stance. Where comparisons were possible, data on the velocity and acceleration appeared reasonable and provide further parameters with which to investigate the role of motion in the rearfoot in the development of pathologic conditions and the effects of intervention on motion in the rearfoot.