Calcaneus or heel bone is the largest of tarsal bones. It projects posteriorly to form the prominence of heel, thus acting as a short lever for muscles of the calf.
Structure of calcaneus:
Calcaneus is irregularly cuboidal in shape. It consists of five different surfaces: Superior, Anterior, Posterior, Plantar and Lateral.
- Superior surface: Its superior surface is divisible into three parts. The most posterior 1/3 is rough and concavo-convex. The middle 1/3 carries the posterior talar facet. The anterior 1/3 is partly articular. Anterior to the articular region, there is a rough depression leading to a groove, the sulcus calcanei, on the medial side. The sulcus calcanei completes the sinus tarsi with talus.
- Anterior surface: The anterior surface is the smallest of all, and is actually an obliquely set concavo-convex articular facet for the cuboid bone.
- Posterior surface: It is divided into three regions: Proximal, Middle and Distal. The middle region is the largest and is limited above by a groove and below by a rough ridge for calcaneal tendon. The distal region is the subcutaneous weight-bearing surface.
- Plantar surface: It is rought and forms the calcaneal tuberosity proximally. There are two laterally extending processes, separated by a notch.
- Lateral surface: It is almost flat and palpable on the lateral aspect of heel. Distally, it presents the peroneal tubercle. There is a deep groove for tendon of peroneus longus and a shallow groove for tendon of peroneus brevis on the lateral surface.
- Medial surface: This surface is vertically concave. The sustantaculum tali projects distally from the distal part of its upper border.Superiorly, the process bears the middle talar facets and inferiorly a groove continuous with that on the talar posterior surface for the tendon of flexor hallucis longus.
Blood supply of calcaneus:
Blood supply of calcaneus is derived from medial and lateral calcaneal arteries. The medial calcaneal artery arises from posterior tibial artery while the lateral calcaneal artery arises from peroneal artery. There is also some degree of blood supply coming from peroneal artery, posterior calcaneal anastomosis, medial and lateral plantar arteries.
Nerve supply to calcaneus:
The calcaneus receives its nerve supply by branches of the tibial, sural and the deep peroneal nerves.
Ossification of calcaneus:
Calcaneus is the only tarsal bone, which has two centers of ossification. The main center appears prenatally in the third month. The second center appears in the sixth year and fuses in fourteenth year. This center covers most of posterior surface and a part of plantar surface.