FOOT MOVEMENT AND TENDON EXCURSION - AN IN-VITRO STUDY

The purpose of this study was to determine tendon excursions resulting from selected foot movement and to derive moment arms with respect to the eversion-inversion and flexion-extension axes of the foot. A lowe r leg-holding device with 6 degrees of freedom was used for the in vit ro investigation of 15 fresh foot-leg specimens. Although high variati on among the subjects existed, there was a pronounced uniformity of te ndon excursion throughout a given foot eversion-inversion or flexion-e xtension range of motion. With reference to the tibialis posterior (1. 00), average invertor moment arms with respect to the foot eversion-in version axis were found to be as follows: flexor digitorum longus, 0.7 5; flexor hallucis longus, 0.62; tibialis anterior, 0.59; soleus, 0.24 ; extensor hallucis longus, 0.22; extensor digitorum longus, -0.26; pe roneus longus, -0.82; and peroneus brevis, -0.86. A trend toward decre asing evertor/invertor moment arms was observed during the ranges of f oot eversion, as well as when the foot was in flexion. Flexor and exte nsor moment arms were found to be substantially dependent on foot flex ion-extension angle. Increasing flexor moment arms were observed when rotating the foot throughout the range from extension to flexion. The obtained results may have significant implications in foot surgery, mu scle function analysis, and general considerations of foot function.