The plantar calcaneonavicular ligament (spring ligament) is a broad thick ligament that spans the space between the sustentaculum tali behind and the navicular bone in front (Fig. 6.107B,C). It supports the head of the talus, takes part in the talocalcaneonavicular joint, and resists depression of the medial arch of the foot.
The calcaneocuboid joint is a synovial joint between: the facet on the anterior surface of the calcaneus, and the corresponding facet on the posterior surface of the cuboid.
The calcaneocuboid joint allows sliding and rotating movements involved with inversion and eversion of the foot, and also contributes to pronation and supination of the forefoot on the hindfoot.
The calcaneocuboid joint is reinforced by the bifurcate ligament (see above) and by the long plantar ligament and the plantar calcaneocuboid ligament (short plantar ligament).
The plantar calcaneocuboid ligament (short plantar ligament) is short, wide, and very strong, and connects the calcaneal tubercle to the inferior surface of the cuboid (Fig. 6.108A). It not only supports the calcaneocuboid joint, but also assists the long plantar ligament in resisting depression of the lateral arch of the foot.
The long plantar ligament is the longest ligament in the sole of the foot and lies inferior to the plantar calcaneocuboid ligament (Fig. 6.108B):
Posteriorly, it attaches to the inferior surface of the calcaneus between the tuberosity and the calcaneal tubercle.
Anteriorly, it attaches to a broad ridge and a tubercle on the inferior surface of the cuboid bone behind the groove for the fibularis longus tendon.
More superficial fibers of the long plantar ligament extend to the bases of the metatarsal bones.
The long plantar ligament supports the calcaneocuboid joint and is the strongest ligament, resisting depression of the lateral arch of the foot.
The tarsometatarsal joints between the metatarsal bones and adjacent tarsal bones are plane joints and allow limited sliding movements (Fig. 6.109).
The range of movement of the tarsometatarsal joint between the metatarsal of the great toe and the medial cuneiform is greater than that of the other tarsometatarsal joints and allows flexion, extension, and rotation. The tarsometatarsal joints, with the transverse tarsal joint, take part in pronation and supination of the foot.
The metatarsophalangeal joints are ellipsoid synovial joints between the sphere-shaped heads of the metatarsals and the corresponding bases of the proximal phalanges of the digits.
The metatarsophalangeal joints allow extension and flexion, and limited abduction, adduction, rotation, and circumduction.
The joint capsules are reinforced by medial and lateral collateral ligaments, and by plantar ligaments, which have grooves on their plantar surfaces for the long tendons of the digits (Fig. 6.109).
Four deep transverse metatarsal ligaments link the heads of the metatarsals together and enable the metatarsals to act as a single unified structure (Fig. 6.109). The ligaments blend with the plantar ligaments of the adjacent metatarsophalangeal joints.
The metatarsal of the great toe is oriented in the same plane as the metatarsals of the other toes and is linked to the metatarsal of the second toe by a deep transverse metatarsal ligament. In addition, the joint between the metatarsal of the great toe and medial cuneiform has a limited range of motion. The great toe therefore has a very restricted independent function—unlike the thumb in the hand, where the metacarpal is oriented 90° to the metacarpals of the fingers, there is no deep transverse metacarpal ligament between the metacarpals of the thumb and index finger, and the joint between the metacarpal and carpal bone allows a wide range of motion.