The calcaneus, also referred to as the calcaneum, (plural: calcanei or calcanea) is the largest tarsal bone and the major bone in the hindfoot. It articulates with the talus superiorly and the cuboid anteriorly and shares a joint space with the talonavicular joint, appropriately called the talocalcaneonavicular joint. The calcaneus transfers most of the body weight from the lower limb to the ground.
The calcaneus is an irregular, roughly box-shaped bone sitting below the talus. Its long axis is oriented along the mid-line of the foot, however deviates lateral to the mid-line anteriorly. It projects posteriorly to form the core of the heel.
The posterior part of the calcaneus is circular, with three facets (superior, middle and inferior). The superior facet is separated from the calcaneal tendon by the retrocalcaneal bursa. The middle facet provides the attachment site for the calcaneal tendon (Achilles tendon). The inferior facet curves anteriorly and is continuous with calcaneal tuberosity on the plantar surface. The plantar surface of the calcaneal tuberosity projects forward on the plantar surface as a medial (larger) and lateral (smaller) process and at its most anterior projection is the calcaneal tubercle, where the short plantar ligament attaches.
On the otherwise fairly smooth lateral aspect of the calcaneus is the fibular trochlea (peroneal tubercle) anterior to the middle of the surface, where the tendons of the fibularis brevis and longus muscles pass above and below respectively. Posterior and superior is the raised area for the attachment of the calcaneofibular part of the lateral collateral ligament of the ankle joint.
Protruding anteromedially from upper margin of the medial surface is the sustentaculum tali which supports the more posterior part of the head of the talus. At its inferior aspect is a groove accommodating the flexor hallucis longus tendon. Superiorly is a cartilage covered facet (middle talar articular facet) for the corresponding middle facet of the head of talus as part of the subtalar joint, which is inclined anteriorly.
The anterior and posterior facets of the talocalcaneal joint are on the superior surface of the calcaneus. The anterior facet is small and the posterior facet is large, inclined anteriorly and located near the middle of the superior surface. Between these two facets runs a fairly deep sulcus, the calcaneal sulcus, which together with the opposing talar sulcus forms the tarsal sinus (sinus tarsi). The tarsal sinus is a large gap between the anterior ends of the talus and calcaneus on its lateral aspect.
The anterior surface has a convex articular facet for the cuboid bone.
- triceps surae, i.e. gastrocnemius and soleus (insertion: middle facet of posterior surface of calcaneus through calcaneal/Achilles tendon)
- abductor hallucis (origin: the medial process of calcaneal tuberosity)
- flexor digitorum brevis (origin: the medial process of calcaneal tuberosity and plantar aponeurosis)
- quadratus plantae (origin: the plantar surface of calcaneus)
- abductor digiti minimi (origin: the medial and lateral process of calcaneal tuberosity)
- extensor digitorum brevis (origin: dorsolateral surface)
- extensor hallucis brevis (origin: dorsal surface, tarsal sinus)
- lateral: lateral collateral ligament of the ankle joint (calcaneofibular ligament)
- inferior: short plantar ligament (at calcaneal tubercle), long plantar ligament (in front of calcaneal tuberosity), plantar aponeurosis (medial process of calcaneal tuberosity proximal to flexor digitorum brevis)
- superior: tarsal sinus ligaments, including:
- cervical ligament
- talocalcaneal interosseous ligament,
- lateral, intermediate, and medial roots of the inferior extensor retinaculum
- bifurcate ligament
- anterior: plantar calcaneonavicular ligament (anterior margin of the sustentaculum tali of the calcaneus)
Superiorly, the calcaneus articulates with the talus at the talocalcaneal joint, also known as the (anatomic) subtalar joint, making contact at anterior, middle and posterior facets.
Anteriorly, the calcaneus articulates with the cuboid (calcaneocuboid joint) bones.
- superior: talocalcaneal joint, talus
- inferior: fat pad of calcaneus, long plantar ligament, short plantar ligament, plantar aponeurosis, quadratus plantae, flexor digitorum brevis
- anterior: calcaneocuboid joint, cuboid bone
- posterior: Achilles tendon, posterior talocalcaneal ligament
- medial: flexor retinaculum and structures deep to it (tendon of flexor hallucis longus, calcaneal branches of posterior tibial artery, tibial nerve, tendon of flexor digitorum longus, tendon of tibialis posterior), abductor hallucis, flexor digitorum brevis, spring ligament, deltoid ligament of ankle, medial talocalcaneal ligament
- lateral: tendon of fibularis brevis, tendon of fibularis longus, superior and inferior fibular retinaculum, calcaneal branches of fibular artery, calcaneofibular ligament, lateral talocalcaneal ligament, abductor digiti minimi, lateral calcaneal branches of sural nerve
- medial calcaneal arteries (from posterior tibial artery)
- lateral calcaneal arteries (from fibular artery)
- posterior calcaneal arterial anastomosis (by above mentioned)
- medial and lateral plantar arteries
- artery of the tarsal sinus and tarsal canal (branches of lateral tarsal artery)
- tibial nerve
- sural nerve
- deep fibular nerve
- talocalcaneal coalition
- calcaneonavicular coalition
- os calcaneus secundarius
- enlarged peroneal tubercle
- retrotrochlear eminence
- assimilated os sustentaculum tali