Tarsals

Introduction

Introduction to the Tarsal Bones

The tarsus is the proximal part of the foot, composed of seven irregularly shaped short bones: the talus, calcaneus, navicular, medial cuneiform, intermediate cuneiform, lateral cuneiform, and cuboid. Together they form the bony framework of the hindfoot and midfoot, transmit body weight from the leg to the forefoot, and provide the mechanical basis for the longitudinal and transverse arches. Each bone has a unique shape and specific articular relationships that contribute to the complex movements of the ankle, subtalar, and transverse tarsal joints. The tarsals are also the site of common fractures, dislocations, and degenerative conditions.

Study

1. General Arrangement of the Tarsus

The seven tarsal bones are arranged in two rows: the proximal (hindfoot) row consists of the talus superiorly and the calcaneus inferiorly; the distal (midfoot) row, from medial to lateral, consists of the medial cuneiform, intermediate cuneiform, lateral cuneiform, and cuboid. The navicular is interposed between the talus and the cuneiforms, forming part of the medial column. The bones are linked by strong interosseous, dorsal, and plantar ligaments that maintain the arches.

2. Talus

The talus is the second largest tarsal bone and the only one to articulate with the leg bones. It consists of a body, neck, and head. The body bears the trochlea (dome), which articulates with the distal tibia and fibula to form the ankle mortise. Posteriorly, the body has a posterior process with medial and lateral tubercles, separated by a groove for the flexor hallucis longus tendon. The lateral tubercle may be separate, forming an os trigonum. Inferiorly, the body articulates with the calcaneus at the subtalar joint via the posterior calcaneal facet. The neck is a constricted region between the body and head, roughened inferiorly for the talocalcaneal interosseous ligament within the sinus tarsi. The head is directed anteriorly and medially, articulating with the navicular (anteriorly) and the calcaneus (inferiorly via the anterior and middle calcaneal facets). The talus has no muscular attachments; it relies on its rich ligamentous and capsular attachments for vascular supply, primarily from the artery of the tarsal canal (posterior tibial artery) and sinus tarsi (peroneal artery).

3. Calcaneus

The calcaneus is the largest tarsal bone, forming the heel. It is an elongated, irregular bone with six surfaces. The posterior surface receives the insertion of the Achilles tendon (calcaneal tendon) on its middle roughened area. The superior surface bears three articular facets (posterior, middle, anterior) for the talus. The middle facet is supported by a bony shelf—the sustentaculum tali—which projects medially and has a groove inferiorly for the flexor hallucis longus tendon. The anterior surface articulates with the cuboid. The lateral surface is marked by the peroneal tubercle, which separates the grooves for peroneus brevis (superior) and peroneus longus (inferior) tendons. The medial surface bears the sustentaculum tali and the groove for the flexor hallucis longus. The inferior surface has the calcaneal tuberosity, which transmits weight to the ground and gives origin to the plantar fascia and the short muscles of the sole. The calcaneus is the first bone to strike the ground during heel strike, and its trabecular architecture reflects the transmission of forces.

4. Navicular

The navicular is a boat‑shaped bone located on the medial side of the foot, between the talus posteriorly and the three cuneiforms anteriorly. Its proximal surface is concave and articulates with the head of the talus. Its distal surface is divided into three facets for the three cuneiforms. A prominent tuberosity on the medial side receives the insertion of the tibialis posterior tendon. The navicular tuberosity is palpable and serves as a landmark; a separate ossicle—the os tibiale externum (accessory navicular)—may be present. The plantar surface has a groove for the tendon of flexor hallucis longus. The navicular is the keystone of the medial longitudinal arch.

5. Cuneiforms

The three cuneiforms are wedge‑shaped bones that form the transverse arch of the foot. The medial cuneiform is the largest, with its wedge‑shaped base directed inferiorly, articulating with the navicular behind, the first metatarsal in front, and the intermediate cuneiform laterally. It receives the insertions of tibialis anterior and peroneus longus. The intermediate cuneiform is the smallest, articulating with the navicular, second metatarsal, medial and lateral cuneiforms. The lateral cuneiform articulates with the navicular, third metatarsal, intermediate cuneiform, and cuboid laterally. The cuneiforms and the first three metatarsals form the rigid medial column of the foot.

6. Cuboid

The cuboid is the most lateral bone of the distal tarsal row, articulating posteriorly with the calcaneus, anteriorly with the fourth and fifth metatarsals, medially with the lateral cuneiform and navicular. Its lateral border is roughened and subcutaneous. The plantar surface is crossed by a deep groove—the peroneal sulcus—for the tendon of peroneus longus, which courses obliquely across the sole. The cuboid forms the lateral column of the foot and is important in lateral foot stability.

7. Ossification of the Tarsals

The tarsal bones ossify in a predictable sequence. The calcaneus begins to ossify at about the sixth fetal month; the talus at the seventh fetal month; the cuboid at about the tenth postnatal month; the lateral cuneiform during the first year; the medial cuneiform during the second year; the intermediate cuneiform during the third year; and the navicular around the third to fourth year. The navicular is the last to ossify and its centre may be irregular, mimicking osteonecrosis (Köhler disease). Accessory ossicles are common, including the os trigonum (posterior talus), os tibiale externum (accessory navicular), os peroneum (near the cuboid in peroneus longus tendon), and os vesalianum (near the fifth metatarsal base).

8. Clinical Considerations

Talar neck fractures are often caused by forced dorsiflexion (e.g., vehicle accidents) and are at high risk of avascular necrosis due to the vulnerable retrograde blood supply to the talus. Calcaneal fractures, most commonly from falls from a height, are often comminuted and can disrupt the subtalar joint, leading to post‑traumatic arthritis. A fall onto the heel can also cause a fracture of the sustentaculum tali. Accessory navicular bone (os tibiale externum) may become symptomatic, presenting as medial foot pain and tenderness. Navicular stress fractures occur in athletes and may be difficult to detect. Cuboid syndrome is a subluxation of the cuboid causing lateral foot pain. Köhler disease is an osteochondrosis of the navicular in children, causing pain and limping. The tarsal tunnel is a fibro‑osseous canal behind the medial malleolus, bounded by the talus and calcaneus, transmitting the tibial nerve and vessels; entrapment here causes tarsal tunnel syndrome.

Summary

Summary of the Tarsal Bones

The tarsus comprises seven bones: talus, calcaneus, navicular, three cuneiforms, and cuboid. The talus articulates with the leg bones and calcaneus, lacks muscle attachments, and has a tenuous blood supply. The calcaneus forms the heel and transmits body weight. The navicular and cuneiforms form the medial column; the cuboid forms the lateral column. Ossification follows a predictable sequence, with the calcaneus earliest and navicular latest. Clinical pathologies include fractures (talar neck, calcaneal), avascular necrosis, accessory ossicles, and tarsal tunnel syndrome.