Arches of the Foot Anatomy
The tarsal and metatarsal bones form two longitudinal arches, medial and lateral. The medial arch is higher, forming the instep of the foot, and consists of the calcaneus, talus, navicular, three cuneiforms, and medial three metatarsals (Figs 6.98, 6.99 & 6.100). The lateral arch comprises the calcaneus, cuboid and lateral two metatarsals (Fig. 6.98). Each arch has an anterior and a posterior pillar, which together transmit body weight to the ground. The posterior pillar of each arch is the same, namely the tubercles on the inferior surface of the calcaneus. However, the anterior pillars are separate, being formed by the heads of the appropriate metatarsals. The arches are important in relation to human bipedalism, as they enhance forward propulsion.
Factors in maintaining the arches include skeletal structure, ligaments, the plantar aponeurosis, and tendons and muscles. Skeletal structure is important in the medial arch, where at its highest point the head of the talus articulates in a wedgelike manner with the navicular anteriorly and the sustentaculum tali posteriorly (Figs 6.101 & 6.102). The head of the talus is supported inferiorly by the plantar calcaneonavicular (spring) ligament (Figs 6.93, 6.101), lying immediately above the tendon of flexor hallucis longus and a slip from the tendon of tibialis posterior, which passes backwards to the sustentaculum tali (Fig. 6.56). Tibialis anterior, through the attachment of its tendon to the first cunei form and first metatarsal, may also support the medial arch, which it raises during inversion.
The lateral arch is supported by the long and short plantar ligaments and the tendon of fibularis longus. Both longitudinal arches derive support from the long flexor tendons of the toes and from the plantar aponeurosis, whose digital slips gain indirect attachment to the proximal phalanges (Fig. 6.96). When the heel rises from the ground the aponeurosis is passively tightened by extension of the toes at the metatarsophalangeal joints, thereby raising the longitudinal arches.