Influence of foot posture on the functioning of the windlass mechanism.

The absence of a functioning windlass mechanism may delay re-supination of the foot during locomotion and put excess stress on the mid-tarsal joint and soft tissues of the foot. The purpose of this study was to describe the foot posture of individuals that have an impaired or absent windlass mechanism. Forty-seven individuals (34 females and 13 males) with a mean age of 26 years were recruited to participate in this study. The Foot Posture Index was used to visually assess the posture of both feet. In addition, a digital gauge was used to measure dorsal arch height and midfoot width in bilateral resting standing. Dorsal arch height and mid-foot width were also measured in non-weight bearing. Finally, for those individuals without a functioning windlass mechanism, the amount of medial wedging needed to restore its function was measured. Subjects with an "absent" or "impaired" windlass mechanism had a mean Foot Posture Index of +6.8 (sd=2.5) compared to +2.5 (sd=3.1) for those with a functioning windlass mechanism. A series of independent t-tests showed that individuals without a functioning windlass mechanism had a more pronated foot posture, a lower dorsal arch height and a wider mid-foot width compared to those that had a functioning windlass mechanism. Finally, an average medial wedge of 5.1mm (sd=2.1) was able to produce a functioning windlass mechanism in those individuals that previously lacked one.