Calcaneus

Contents

Name of bone

Calcaneus (Latin: Os calcis

Location/Articulation

The calcaneus is the largest of the tarsal bones, constituting the heel. The calcaneus is situated at the lower and back part of the foot, serving to transmit the weight of the body to the ground, and forming a strong lever for the muscles of the calf.

Figure 1. In this AP view of the foot, the talus sits above and obscures part of the calcaneus.

Figure 2. In this view, the talus is removed, showing the calcaneus. The sustentaculum tali projects medially to support the middle facet of the talo-calcaneal articulation.

Figure 3. This is an AP view of the ankle. The calcaneus is in red, with the talus directly above it.

Figure 4. A medial view of the foot, showing the calcaneus in red, articulating with the talus above and navicular in front. Both of these articulations can fail to separate, leading to a tarsal coalition.

Figure 5. In this lateral view of the foot, the calcaneocuboid joint is seen.

The main angulations (dorsiflexion, plantar flexion) of the ankle occur at the tibio-talar joint. The calcaneal articulations primarily position the foot relative to the ankle in the various stages of gait and to allow “tilt” (inversion/eversion) of the foot especially on uneven ground.

Figure 6. An AP drawing showing subtalar inversion.

Several important structures can be distinguished on the surfaces of the calcaneus.

Figure 7. Lateral view of the calcaneus. The inverted V depicts a groove for the peroneus longus.

Figure 8. The medial surfaces of the calcaneus. Shown in red are the surfaces for the talar articulation and Achilles attachment (tuberosity). The talar articulation is divided into 3 regions, with the middle supported by the sustentaculum tali, as seen.

The posterior half of the bone is the tuberosity. This is the attachment site of the Achilles tendon calcanei. The superior surface has a V-like depression in which the talus sits. This area is divided into three articular facets:

anterior
middle
posterior.

The middle facet is supported by a projection coursing medially, the sustentaculum tali. The sustentaculum is also an attachment site of the plantar calcaneonavicular ligament and part of the deltoid ligament of the ankle-joint. On the lateral side, there is a peroneal trochlea, under which is a groove for the tendon of the peroneus longus.

The really important message is that the geometry of the calcaneus is complex, and therefore fractures and other processes that distort this anatomy can have severe functional consequences.

Muscle and ligament attachments

The only tendon inserting on the calcaneus is the Achilles tendon, comprising the terminal fibers of the gastrocnemeus and soleus muscles.

Figure 9. A lateral view showing the insertion of the Achilles onto the calcaneus.

The plantar fascia, a band of connective tissue supporting the arch, runs from the tuberosity of the calcaneus to the undersurface of the metatarsal heads.

Figure 10. The plantar fascia, shown in purple, connects the calcaneus to the metatarsal heads and keeps the arch of the foot (black) arched, just as the string keeps the limbs of a bow under tension.

The extensor digitorum brevis, the flexor digitorum brevis, the abductor hallucis and abductor digit minimi all originate from the calcaneus as well.

Surface anatomy

Figure 11. In this photo, the approximate location of the calcaneus is shown, along with the attachment of the Achilles.

Figure 12. In this view from behind, the calcaneus is outlined.

Factoids

An ossification center is developed during the 4th through 7th intrauterine months.
Subject to tarsal coalition.
Fractures from axial load.
Subtalar arthrosis may form.
Heel pain may be from stress fractures of the calcaneus.