The Talus is the second largest tarsal bone. It lies between the tibia above and the calcaneum below, gripped on the sides by the two malleoli.
It has a head, a neck and a body.
The rounded head is directed forwards.
The trochlear articular surface of the body is directed upwards, and the concave articular surface downwards.
The body bears a large triangular, facet laterally, and a comma-shaped facet medially.
It is directed forwards and slightly downwards and medially.
Its anterior surface is oval and convex. The long axis of this surface is directed downwards and medially. It articulates with the posterior surface of the navicular bone.
The inferior surface is marked by three articular areas separated by indistinct ridges. The posterior facet is largest, oval and gently convex; it articulates with the middle facet of the calcaneum. The anterolateral facet articulates with the anterior facet of the calcaneum, and the medial facet with the spring ligament.
- This is the constricted part of the bone between the head and the body.
- It is set obliquely on the body, so that interiorly it extends further backwards on the medial side than on the lateral side. However, when viewed from dorsal side, the long axis of the neck is directed downwards, forwards and medially. The neck-body angle is 130 to 140 degrees in infants and 150 degrees in adults. The smaller angle in young children accounts for the inverted position of their feet.
- The medial part of its plantar surface is marked by a deep groove termed the sulcus tali. The sulcus tali lies opposite the sulcus calcanei on the calcaneum, the two together enclosing a space called the sinus tarsi.
- In habitual squatters, a squatting facet is commonly found on the upper and lateral part of the neck. The facet articulates with the anterior margin of the lower end of the tibia during extreme dorsiflexion of the ankle.
The body is cuboidal in shape and has five surfaces.
The superior surface bears an articular surface, which articulates with the lower end of the tibia to form the ankle joint. This surface is also called the trochlear surface. It is convex from before backwards and concave from side to side. It is wider anteriorly than posteriorly. The medial border of the surface is straight, but the lateral border is directed forwards and laterally.
The inferior surface bears an oval, concave articular surface which articulates with the posterior facet of the calcaneum to form the subtalar joint.
The medial surface is articular above and non- articular below. The articular surface is comma- shaped and articulates with the medial malleolus.
The lateral surface bears a triangular articular surface for the lateral malleolus. The surface is concave from above downwards, and its apex forms the lateral tubercle of the talus. The posterior part of the lateral surface is separated from the trochlea by an ill-defined, small triangular area which articulates with the inferior transverse tibiofibular ligament.
The posterior surface is small and is marked by an oblique groove. The groove is bounded by medial and lateral tubercles. A posterior tubercle is also present. It is occasionally separate and is then called the os trigonum.
Attachments on the Talus
The talus is devoid of muscular attachments, but numerous ligaments are attached to it because it takes part in three joints.
- The following ligaments are attached to the neck,
- The distal part of the dorsal surface provides attachment to the capsular ligament of the ankle joint and to the dorsal talonavicular ligament. The proximal part of the dorsal surface lies within the ankle joint,
- The inferior surface provides attachment to the interosseous talocalcanean and cervical ligaments,
- The lateral part of the neck provides attachment to the anterior talofibular ligament.
- The lower, non-articular part of the medial surface of the body gives attachment to the deep fibres of the deltoid ligament.
- The groove on the posterior surface lodges the tendon of the flexor hallucis longus. The medial tubercle provides attachment to the superficial fibres of the deltoid ligament above and the posterior talocalcanean ligament below.
The talus ossifies from one centre which appears during the 6th month of intrauterine life.