The medial surface of the calcaneus is concave and has one prominent feature associated with its upper margin (the sustentaculum tali; Fig. 6.98A), which is a shelf of bone projecting medially and supporting the more posterior part of the head of the talus.
The underside of the sustentaculum tali has a distinct groove running from posterior to anterior and along which the tendon of the flexor hallucis longus muscle travels into the sole of the foot.
The superior surface of the sustentaculum tali has a facet (middle talar articular surface) for articulation with the corresponding middle facet on the head of the talus.
Anterior and posterior talar articular surfaces are on the superior surface of the calcaneus itself (Fig. 6.98A):
The anterior talar articular surface is small and articulates with the corresponding anterior facet on the head of the talus.
The posterior talar articular surface is large and is approximately near the middle of the superior surface of the calcaneus.
Between the posterior talar articular surface, which articulates with the body of the talus, and the other two articular surfaces, which articulate with the head of the talus, is a deep groove (the calcaneal sulcus; Fig. 6.98A,C).
The calcaneal sulcus on the superior surface of the calcaneus and the sulcus tali on the inferior surface of the talus together form the tarsal sinus, which is a large gap between the anterior ends of the calcaneus and talus that is visible when the skeleton of the foot is viewed from its lateral aspect (Fig. 6.99).
The intermediate tarsal bone on the medial side of the foot is the navicular (boat shaped) (Fig. 6.96). This bone articulates behind with the talus and articulates in front and on the lateral side with the distal group of tarsal bones.
One distinctive feature of the navicular is a prominent rounded tuberosity for the attachment of the tibialis posterior tendon, which projects inferiorly on the medial side of the plantar surface of the bone.
From lateral to medial, the distal group of tarsal bones consists of (Fig. 6.96):
The cuboid (Greek for “cube”), which articulates posteriorly with the calcaneus, medially with the lateral cuneiform, and anteriorly with the bases of the lateral two metatarsals—the tendon of the fibularis longus muscle lies in a prominent groove on the anterior plantar surface, which passes obliquely forward across the bone from lateral to medial.
Three cuneiforms (Latin for “wedge”)—the lateral, intermediate, and medial cuneiform bones, in addition to articulating with each other, articulate posteriorly with the navicular bone and anteriorly with the bases of the medial three metatarsals.
There are five metatarsals in the foot, numbered I to V from medial to lateral (Fig. 6.100). Metatarsal I, associated with the great toe, is shortest and thickest. The second is the longest.
Each metatarsal has a head at the distal end, an elongate shaft in the middle, and a proximal base.
The head of each metatarsal articulates with the proximal phalanx of a toe and the base articulates with one or more of the distal group of tarsal bones. The plantar surface of the head of metatarsal I also articulates with two sesamoid bones.
The sides of the bases of metatarsals II to V also articulate with each other. The lateral side of the base of metatarsal V has a prominent tuberosity, which projects posteriorly and is the attachment site for the tendon of the fibularis brevis muscle.
The phalanges are the bones of the toes (Fig. 6.100). Each toe has three phalanges (proximal, middle, and distal), except for the great toe, which has only two (proximal and distal).
Each phalanx consists of a base, a shaft, and a distal head: