Foot inversion is defined as turning the footsole inwards, and eversion is turning the ... Van Zwieten, K.J., Lippens, P.L., Lamur, K.S. (2003) Aspects of arthrology.
NON-SAGITTAL MOVEMENTS OF THE FOOT DURING THE SWING PHASE F.H.M. Narain 1, K.J. van Zwieten 2, I. Robeyns 2, M. Vandersteen 2, S. Biesmans 2, K.P. Schmidt 2, A. Reyskens 2, P. L. Lippens 2, R.V. Mahabier 1, K.S. Lamur 1 1 2
Department of Anatomy, University of Suriname, Paramaribo, Suriname
Department Medische Basiswetenschappen, BioMed Institute, Universiteit Hasselt, Diepenbeek, Belgium
Introduction: Tibialis anterior muscle, a main foot dorsiflexor, causes foot inversion too. Foot inversion is defined as turning the footsole inwards, and eversion is turning the footsole outwards. In this study, the moment arm length of m. tibialis anterior respective to the axis of foot inversion was measured on biplanar radiograms, made of ten dissected anatomical specimens of lower leg and foot. Our outcome data were compared to movie stills of freely moving feet in vivo, especially during the swing phase of gait. Impaired gait and loss of stability, by decreasing tibialis anterior functions, do belong to the major symptoms of various chronic neuropathies like Multiple Sclerosis.
Backgrounds: Quadrupedal locomotion in arboreal primates and their precursors is characterized by a.o. moving forward of the body in the parasagittal plane, while the forefoot keeps clinging to the substratum. This, as a consequence, imposes an external rotation on the lower leg, which in turn is transferred to an inversion movement of the foot, thanks to the cardan-like function of the ankle joint. Such rotational movements in the tarsus include the calcaneo-cuboid pivoting, in lower primates and their precursors, as well as in the two-legged hominids including man. The axis of primate foot inversion and eversion runs through this calcaneo-cuboid pivot, as it does in a primate predecessor, the opossum. Remarkably, at the beginning of stance, opossum and lower primates lack initial heel contact, while higher primates including man have heel contact from touchdown on. A prerequisite for this heel strike at the beginning of stance in bipedal human gait is dorsiflexion of the foot by activity of the foot extensor muscles such as m. tibialis anterior, just prior to touchdown.
Material and methods: In each of ten otherwise normal human anatomical specimens, prior to radiography, metal marking wires were wound around the tendon of m. tibialis anterior, in order to identify precisely the muscle’s course on antero-posterior and mediolateral radiograms of the foot.
The longitudinal axis of inversion and eversion of the transverse tarsal joint (Chopart’s joint) was introduced in tracings made of each radiogram, by drawing an oblique line connecting the lateral tubercle of tuber calcanei and the cuboid’s processus calcaneus, up to the first interdigital cleft of each foot. By combining the measurements from each orthogonal pair of biplanar radiograms, the distance between the straight line representing the course of the tibialis anterior tendon, and the axis of foot inversion, at the point of their crossing, was calculated. This distance represents the moment arm length of tibialis anterior muscle, respective to the axis of inversion, in the specimens.
Results and conclusions: The average length of the inversion-eversion moment arm of m. tibialis anterior, measured in 10 anatomical specimens, is 2.3 cm. This is in accordance with comparable recently published in vivo data (Lee & Piazza, 2007). To acquire data on live foot movements in the swing phase as well, detailed anterior views of feet during barefoot stride were studied, derived from random movie stills. At the end of each swing phase just prior to touchdown, the visibly active m. tibialis anterior initiating foot dorsiflexion, can be observed to cause clearly visible simultaneous foot inversion as well. Directly after heel strike, this inversion abruptly ceases in order to guarantee optimal positioning of the foot during the single-support phase of stance, thus maintaining stability.
References
Narain, F.H.M., Van Zwieten, K.J., Lippens, P.L., Lamur, K.S. (2003) Aspects of arthrology in the lower leg of the opossum. European Journal of Morphology, 41, 1, 68.
Lee, S., Piazza, S. (2007) In vivo measurement of the inversion-eversion moment arms of gastrocnemius and tibialis anterior. In: Proceedings of the 31st Annual Meeting of the American Society of Biomechanics, Stanford, CA, August 22-25, 2007, P9-6.
Keywords : Gait analysis, Lower leg neuropathy, Foot inversion movements
