[Biomechanics of the joints of the large toe. Shape and movement of the first tarsometatarsal joint and of the medial cuneonavicular joint].

90% of the first (hallucal) tarsometatarsal joints are screw-shaped; the axis is directed upwards to the front touching the lateral edge of the joint. Thus the plantar flexion is inevitably accompanied by an adduction and a pronation, and vice versa a dorsiflexion is consequently accompanied by an abduction and a supination, when the articular surfaces exactly slide along each other. 10% of these joints, however, are ellipsoid-shaped; in this case the distal articular surface of the medial cuneiform bone has the form of an ovoid head, and a strong ligament situated next to the lateral edge of the joint effects the same kind of motion described above. The medial cuneonavicular joint is always ellipsoid-shaped, the head of which is made up by the medial facet of the distal articular surface of the navicular bone. Each of the two joints mentioned has a considerable range of mobility.