The function of the muscles of the lower leg in relation to movements of the tarsus

Abstract

This study was designed to obtain more information regarding the function of the lower leg muscles in relation to the movements of the tarsus. Until now, no quantitative data have appeared in the literature concerning the movements of the tarsal bones; the authors began therefore, with an investigation of these latter movements. In the functional-anatomical part of this study bone ligament preparations of lower leg and foot were mounted in the loaded position in an apparatus, called the cage. In this manner a combination of supination of the foot with exorotation of the lower leg or of pronation of the foot with endorotation of the lower leg could be studied. Firstly, the rotations of the tarsal bones during supination were measured. Thereafter the tendon slip of the lower leg muscles during movement of the tarsus was measured in four of these preparations from the same positions mentioned above. It appears that, during maximal supination of the tarsus, the navicular rotates 29° and the cuboid 23° in a supinatory fashion in a more or less frontal plane. The mobility of the navicular with respect to the cuboid is slight. The talus exorotates 33° in a more or less horizontal plane. The navicular endorotates 33° in the same plane with respect to the talus. The calcaneus supinates 120 and exorotates through 16°. It appears from these measurements that the movements of the bones in the tarsus during supination are considerable. The remodelling of the tarsus can be explained from these findings. The author has to correlate the experiments in vitro with the findings of the investigations in vivo. E.M.G. recordings were made of the eleven lower leg muscles and of one foot muscle in two groups of experimental subjects. These subjects made with their feet the same supinatory movements as performed in the experiments in vitro. The author calculated and expressed as a percentage how frequently a muscle was active during a number of given movements. Tibialis posterior and flexor digitorum are both active during supination in a high frequency. In addition to the supinatory movements, a so-called clawing movement was introduced. In this clawing movement both arches, medial and lateral, became higher. There is no exorotation of the lower limb and talus. Three muscles are active in a high frequency during simultaneous raising of the medial and lateral arches, namely, tibialis anterior, extensor digitorum and the peroneus brevis.