Talus forms the link between foot and leg, through the ankle joint. It forms lower part of ankle joint by articulating with medial and lateral malleoli. The talus is second largest tarsal bone. Talus is unique because of two important features. First, its blood supply is retrograde and second, 70% of it is covered by articular cartilage. Although it is more or less irregular in shape but still it can be subdivided into three parts:head, neck and body.
Structure of Talus:
- Head: It carries the articular surface for navicular bone. The plantar surface of head contains three articular areas, separated by smooth ridges. The most posterior and largest is known as sustantaculum tali, which rests on a shelf like projection.
- Neck: Neck is the narrow region between head and body. It presents many rough surfaces of attachments of ligaments. It contains a deep sulcus tali, which after articulation of talus and calcanues, forms a roof to the sinus tarsi. This sinus is occupied by interosseous talocalcaneal and cervical ligaments.
- Body: The body is somewhat cuboidal in shape. It is covered dorsally by a trochlear surface, which articulates with distal end of tibia. Lateral surface is triangular, smooth and verticall concave for articulation with lateral malleolus. The medial surface is covered by comma shaped facet for articulation with medial malleolus.
Posterior surface of body of talus is rough and is marked by a groove for tendon of flexor hallucis longus. The groove lies between two tubercles, the lateral of which is larger.
Muscle attachments of Talus:
Although numerous ligaments make attachment to talus, no muscles are attached to it. The number of ligaments attached to it is on the higher side because it takes part in formation of three different joints viz, ankle, subtalar and talocalcaneonavicular.
Blood Supply of talus:
Blood supply of talus is not very profuse because of lack of muscular attachment. Talus is unique because its blood supply is retrograde, which means that the arteries enter the bone at distal end. The extraosseous blood supply comes from posterior tibial artery, dorsalis pedis artery and peroneal arteries.
The intraosseous blood supply of the talar head comes medially from branches of the dorsalis pedis and laterally from branches from the anastomosis between the artery of the tarsal canal and the tarsal sinus.
Nerve supply to talus:
Talus is innervated by branches from deep peroneal, posterior tibial, saphenous and sural nerves.
Ossification of talus:
Normally the bone ossifies from a single center, which appears prenatally at 6 months. The posterior process of body of talus is a separate bone is 5% individuals and there is a separate ossification center for it, which appears between 8 and 11 years.
Fractures of talus:
Because of no muscular attachment and the fact that 70% of of its surface is covered by articular cartilage, the displaced neck fractures of talus can result in avascular necrosis of bone.