Active and passive mechanisms in the control of heel supination

Abstract

Heel supination when standing tiptoe may be related to the function of tibialis posterior, the plantar aponeurosis or the skeletal structure of the foot. We attempted to determine the relative importance of these different mechanisms in 20 individuals. Heel supination was measured in response to toe extension, tiptoe standing and using a specially designed platform that enabled tiptoe standing without toe extension, thus eliminating the windlass mechanism. Intra-observer and intersubject variability were assessed. Passive toe extension produced 5.0 ± 3.2° heel supination and normal tiptoe standing (active and passive mechanisms) 7.8 ± 3.5°. Standing tiptoe on the platform without toe extension (active mechanism alone) caused heel supination to 3.3 ± 2.7°. This simple study demonstrates that heel supination on standing tiptoe is caused by a number of mechanisms. The windlass mechanism of the plantar aponeurosis would appear to contribute, on average, 50% of this movement in most individuals, although there was significant intersubject variation. Complete loss of heel supination associated with tibialis posterior rupture implies failure of other mechanisms also.