The foot itself can be divided into 3 parts
- Hindfoot or rearfoot
The talus is the second largest tarsal bone, and is situated above the calcaneus in the hindfoot.
Talus is a unique bone. Two thirds of the talar surface is covered with articular cartilage. Neither tendons nor muscles insert or originate from this bone.
The talus articulates with 4 bones: the tibia, fibula, calcaneus, and navicular.
Structure of Talus
Talus is composed of body, neck and head. It also has two processes- the lateral and posterior.
Body of Talus
The body is cuboidal in shape and has five surfaces.
- Superior Surface
- Inferior Surface
- Medial Surface
- Lateral surface
- Posterior Surface
The superior surface is also called trochlear surface and bears an articular surface, which articulates with the lower end of the tibia to form the ankle joint. It is shaped like a pulley, with the groove of the pulley termed the trochlea, closer to the medial border.
It is convex from before backwards and concave from side to side.
In front, it is continuous with the upper surface of the neck of the bone.
It bears an oval, concave articular surface called posterior facet or posterior calcaneal articular surface which articulates with the posterior facet of the calcaneum to form the subtalar joint.
The posterior calcaneal articular surface is deeply concave in the direction of its long axis, which runs forward and lateralward at an angle of about 45° with the median plane.
It is continuous above with the superior articular surface with posterior part of the being separated from the trochlea by an ill-defined, small triangular area which articulates with the inferior transverse tibiofibular ligament.
Along the posteroinferior border of this lateral surface lies a groove for the attachment of the posterior talofibular ligament.
The anterior talofibular ligament inserts at anterior border of the triangular lateral process at 2 tubercles.
A posterior tubercle is also present . Sometimes it is separate and in such cases, it is called os trigonum.
The posterolateral tubercle is more prominent of the two and gives attachment to the posterior talofibular ligament.
Neck of Talus
This is the constricted part of the bone between the head and the body. It is set obliquely on the body, so that inferiorly it extends further backwards on the medial side than on the lateral side. However, when viewed from dorsal side, the long axis of the nack is directed downwards, forwards and medially. The neck-body angle is 130 to 140 degrees in infacts and 150 degrees in adults.
This portion of the talus is most vulnerable to fracture.
The superior surface of the neck is limited posteriorly by the anterior border of the trochlea of the talus (the dome or body) and anteriorly by the articular surface of the talar head. The tibiotalar capsule inserts along this superior surface just proximal to the insertion of the capsule of the talonavicular joint.
The lateral surface of the neck is concave and is continuous below with the deep groove for the interosseous talocalcaneal ligament. It provides an insertion for the medial aspect of the inferior extensor retinaculum.
The inferior surface of the neck forms the roof of the sinus tarsi and sinus canal. It forms a deep groove called sulcus tali which separates the posterior facet of body and middle facets on the headi. The groove runs obliquely forward and lateralward, becoming gradually broader and deeper in front. A similar groove is on upon the upper surface of the calcaneus, and both the grooves together form a tarsal canal termed the sinus tarsi. It contains interosseous talocalcaneal ligament.
Inferior surface of the neck contains numerous holes for nutrient arteries.
The medial surface provides an area for insertion of the talonavicular ligaments.
Head of Talus
Head of the talus is directed forwards and slightly downwards and medially. Its anterior articular 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 middle 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.
The head of the talus nests within an articulation known as the acetabulum pedis, or foot socket formed by the calcaneal middle and anterior surfaces connected to the large navicular articular surface by the inferior and superomedial calcaneonavicular ligaments.
Following video would make understanding the anatomy easier.
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 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.
- 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 attachments to the interosseus talo-calcanean and cervical ligaments.
- The lateral part of the neck provides attachment to the anterior talofibular ligament.
Ossification of Talus
The talus ossifies from one centre which appears during the sixth month of intrauterine life.
Blood Supply of The Talus
Talus bone is supplied by posterior tibial and anterior tibial artery through various branches. Negligible contribution can be thorugh peroneal artery.
Following video would explain importance of blood supply of talus.
Posterior Tibial Artery
Artery of the Tarsal Canal
Artery of tarsus canal arises from posterior tibial around 1 cm proximal to its division and passes anterior to flexor digitorum longus. It enters the tarsal canal [other structure present is the interosseous ligament] and gives branches to talus which enter the talus from medial and inferior side.
It also anastomoses with arteries in tarsal sinus to produce vascular sling
It is a branch of the artery of the tarsal canal. Sometimes it takes its origin from the posterior tibial artrey.
It travels between two parts of deltoid ligament and gives branches that enter via medial side of the talar body
It is responsible for blood supply to the medial half of the talar body
Anterior Tibial Artery
Superior neck branches are given by Dorsalis Pedis.
It supplies the lateral half of the talar body
Distribution of of blood supply of the talus
- Head of Talus
- Medially from branches of the Dorsalis Pedis
- Laterally from the artery of the Tarsal Sinus
- Body of talus
Talus is common bone to get fractured. Neck part of this bone is quite vulnerable to fracture and may cause necrosis of talus due to disruption of blood supply
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 tibia during extreme dorsiflexion of the tibia during extreme dorsiflexion of the ankle.
The acetabulum pedis has a variable volume capacity and adapts to the changing position of the talar head during gait.
Side Determination of Talus
- 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.
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