Joints of the Foot Anatomy
These joints include those between the tarsal bones, the metatarsals and the phalanges. They are all synovial and have shapes related to their movements.
Although the tarsal joints are articulations between individual bones, they are usually classified into groups according to their locations (Fig. 6.92). The posterior tarsal group involves the talus and calcaneus; the midtarsals are between the talus and navicular on the medial side of the foot and between the calcaneus and cuboid on the lateral side; the anterior tarsals include the navicular, three cuneiforms and cuboid. All these joints are extremely stable.
There are two articulations between the talus and calcaneus, each with a separate synovial cavity. Posteriorly is a saddle joint between the convex surface on the middle third of the calcaneus and the reciprocally concave surface on the body of the talus (Fig. 6.93). Anteriorly, two small flat facets on the anterior part of the calcaneus, including the sustentaculum tali, articulate with corresponding facets beneath the head of the talus (Fig. 6.93).
The head of the talus forms a ballandsocket joint with the posterior surface of the navicular. This joint shares a common synovial cavity with the anterior part of the talocalcaneal articulation. The combined joint, which involves the head of the talus, is termed the talocalcaneonavicular joint. The posterior talocalcaneal and talocalcaneonavicular joints form the subtalar joint.
At this plane joint, the flat anterior surface of the calcaneus articulates with the posterior surface of the cuboid (Fig. 6.92).
Other tarsal joints
Plane joints occur between the opposing surfaces of the navicular, the three cuneiforms and the cuboid (Fig. 6.92) and their synovial cavities freely communicate.
Capsules and ligaments
The fibrous capsules are attached around the margins of the articular surfaces. Short ligaments on the dorsum of the joints (Fig. 6.93) reinforce the capsules and, with the interosseous ligaments (Fig. 6.92), keep the articulating surfaces closely opposed. The strong interosseous talocalcaneal ligament (Fig. 6.93) in the sinus tarsi holds the talus and calcaneus together. The stem of the bifurcated ligament attaches to the anterior part of the calcaneus and its limbs to the navicular and cuboid. Beneath the tarsals, the long and short plantar ligaments (Fig. 6.56) unite the plantar sur faces of the calcaneus and cuboid. The plantar calcaneonavicular (spring) ligament (Fig. 6.93) unites the navicular and sustentaculum tali, supporting the head of the talus and completing the socket by which the head articulates with the navicular and calcaneus.
The most mobile of the tarsal joints is the talocalcaneonavicular joint. Its ballandsocket shape permits rotation around an oblique axis, which passes upwards, forwards and medially through the neck and head of the talus. This rotation, together with gliding movements at the other tarsal joints, enables the anterior part of the foot to twist in respect to the more posterior part. These twisting movements involve raising either the medial or lateral border of the foot. Raising the medial border is called inversion and is produced by tibialis anterior and posterior, assisted by extensor hallucis longus. Raising the lateral border is called eversion and is brought about by fibularis longus, brevis and tertius.
Because of the oblique axis of the talocalcaneonavicular joint, inversion is always accompanied by plantar flexion and adduction of the foot, while eversion is accompanied by dorsiflexion and abduction. These additional movements can be compensated by simultaneous movements at other joints. Thus, the plantar flexion accompanying inversion can be offset by slight dorsiflexion at the ankle joint, while adduction can be offset by lateral rotation of the leg at the knee and hip joints.
The tarsal joints are innervated by branches of the medial and lateral plantar nerves and the deep fibular nerve.
Tarsometatarsal and intermetatarsal joints
These are plane joints in which the bases of the fourth and fifth metatarsals articulate with the cuboid, while the bases of the first, second and third metatarsals articulate with the respective cunei forms (Fig. 6.94). Dorsal, plantar and interosseous ligaments rein force the joint capsules. These joints allow gliding movements during alterations in the height of the arches. Innervation is by plantar and deep fibular nerves.
In each of the ballandsocket metatar sophalangeal joints, the metatarsal head articulates with the base of the proximal phalanx and the associated fibrocartilaginous plantar plate (Figs 6.95 & 6.96). A capsule enclosing the articular surfaces is reinforced on each side by a collateral ligament and dorsally by the extensor expansion. The principal movements are flexion and extension with only minimal abduction or adduction. The first metatarsophalangeal joint is especially important, bearing body weight during walking. Two sesamoid bones (Figs 6.101 & 6.102) are usually present in the plantar plate of this joint, closely associated with the insertions of the intrinsic muscles of the great toe (p. 282).
The interphalangeal joints (Figs 6.95 & 6.97) are hinge joints, allowing flexion and extension. The muscles moving these joints are described on p. 282. The joints of the toes are innervated by digital branches of the medial and lateral plantar nerves.