Calcaneus

Bony landmarks

Articulations

The calcaneus provides insertion points for the abductor hallucis and the abductor digit minimi muscles. At the back of the heel, the Achilles tendon inserts into the rough area located on the superior side. This tendon, as well as other ligaments and muscles, is necessary for standing and walking. Therefore a broken or fractured calcaneus will cause difficulty in standing and walking.

There are two articulations (with three facets) with the talus and one saddle-shaped articulation with the cuboid. The sustentaculum tali is a horizontal shelf that arises from the anteromedial portion of the calcaneus. The superior surface is concave and articulates with the middle calcaneal surface of the talus. The inferior surface has a groove for the tendon of flexor hallucis longus.

The sustentaclulum tali bears the greatest weight per area and also has a lot of soft tissue structures attaching around it. The lateral wall of the calcaneus is thin and has attachments for the calcaneofibular ligament and the osseus reflection of the peroneal tendons. On the medial aspect, the bone is thicker and there is close proximity to the toe flexors and neurovascular structures.

Muscle and ligament attachments

As the calcaneus is the largest of the bones in the foot, it provides a large surface area for the complex attachment of many muscles and ligaments. The calcaneal sulcus provides attachments for the:

• interosseous,
• talocalcaneal,
• cervical ligaments and
• medial root of the inferior extensor retinaculum 

There is also a non-articular area on the calcaneus, distal to the posterior talar facet which provides an attachment surface for:

• extensor digitorum brevis
• the main band of the inferior extensor retinaculum
• the stem of the bifurcate ligament

There is a prominent medial margin on the medial process of the calcaneal tuberosity which provides attachments for the superficial part of the flexor retinaculum and distally the plantar aponeurosis. Some muscles also attach there including abductor hallucis and flexor digitorum brevis. The abductor digiti minimi attaches mainly to the lateral process however it does extend medially onto the medial process.

There is a rough region between these processes which extends to the anterior tubercle distally. It provides an attachment surface for the long plantar ligament. Near this is the attachment of the head of the flexor accessories muscle. The short plantar ligament is attached to the tubercle and the area distal to it.

Plantaris attaches to the posterior surface near the calcaneal tendon. The fibular tendons cross on the lateral surface and the calcaneofibular ligament attaches just proximal to the fibular trochlear. Many structures also attach around the sustentaculum tali. Its plantar surface is grooved by the tendon of flexor hallucis longus and this gives attachments to the deep part of the flexor retinaculum.

The plantar calcaneonavicular ligament attaches to the medial margin of the sustentaculum tali. Proximal to this are the attachments of the tendon of tibialis posterior, superficial fibres of the deltoid ligament and medial talocalcaneal ligaments. On the margin of the sustentaculum tali are the attachments of the tendon of flexor digitorum longus and the large medial head of flexor accessorius is attached distal to the groove for flexor hallucis longus.

Role with the talus and cuboid

The calcaneus articulates with two bones: the talus and the cuboid. There are three articular surfaces for the talus. The largest is the slightly convex oval surface for the body of the talus. Anteromedial to this is the medial articular surface for the talus on the dorsal aspect of the sustentaculum tali. Anterolateral to this surface is the small anterior facet for the talus, which may sometimes blend with the medial facet. The latter two facets are shallowly concave. The distal end forms an obliquely directed, oval, articular surface that is convex in the transverse plane and concave in the vertical plane. This surface articulates with the cuboid bone.