Talus

The talus is a centrally located tarsal bone in the ankle that forms the primary connection between the leg and the foot. It articulates superiorly with the tibia and fibula to form the ankle (tibiotalar) joint and inferiorly with the calcaneus and navicular bones to complete the subtalar and talonavicular joints. Unlike most bones, the talus has no direct muscular attachments, which gives it a unique role in weight transmission and multidirectional motion while relying entirely on ligamentous and articular support.

Structure

The talus is an irregular, roughly cuboidal bone divided into three major parts: the body, neck, and head. It is covered extensively with articular cartilage and contains a central cancellous core surrounded by dense cortical bone. Approximately 60–70% of its surface is covered in hyaline cartilage, which facilitates smooth articulation but limits direct vascular penetration.

Body of Talus

• Trochlea: The superior surface of the body, articulates with the distal tibia and forms the main surface of the ankle joint. It is wider anteriorly than posteriorly, allowing greater stability in dorsiflexion.
• Medial surface: Articulates with the medial malleolus of the tibia.
• Lateral surface: Articulates with the lateral malleolus of the fibula; features the lateral process, a common site for fractures.
• Posterior process: Contains the groove for the flexor hallucis longus tendon; may include a separate ossicle called the os trigonum.

Neck of Talus

• Connects the body to the head and projects anteromedially
• Angled about 10–20° medially from the body
• Contains vascular foramina that transmit arteries into the body

Head of Talus

• Articulates anteriorly with the navicular bone
• Forms part of the talonavicular joint, essential for inversion and eversion
• Inferior surface articulates with the anterior and middle facets of the calcaneus

Location

The talus is located between the leg and the foot, forming the keystone of the ankle joint complex. It lies superior to the calcaneus and posterior to the navicular. It is the second largest tarsal bone and centrally positioned within the hindfoot.

• Superior: Tibia and fibula
• Inferior: Calcaneus
• Anterior: Navicular
• Posterior: Achilles tendon (via calcaneus) and flexor hallucis longus tendon groove

Function

• Weight transmission: Transfers body weight from the tibia to the foot during standing and gait
• Motion facilitation: Allows dorsiflexion and plantarflexion at the ankle joint, and inversion/eversion via the subtalar and talonavicular joints
• Structural keystone: Central to the medial longitudinal arch of the foot

Articulations

The talus articulates with four bones to form three major joints:

Articulating Bone	Joint	Joint Type
Tibia	Tibiotalar (ankle) joint	Synovial hinge
Fibula	Tibiotalar (ankle) joint	Synovial hinge
Calcaneus	Subtalar joint	Synovial plane
Navicular	Talonavicular joint	Synovial ball-and-socket

Blood Supply

The blood supply of the talus is precarious and predominantly extraosseous, making it highly susceptible to avascular necrosis after fracture or dislocation. It is supplied by three main sources:

• Posterior tibial artery: Via the artery of the tarsal canal and the deltoid branch, supplying the body and medial aspect
• Dorsalis pedis artery: Via the artery of the sinus tarsi, which enters from the lateral side
• Perforating peroneal artery: Contributes through lateral anastomoses

These arteries anastomose within the tarsal canal and sinus tarsi. The limited vascular access through the non-articular neck region is crucial for internal perfusion.

Nerve Supply

Innervation to the talus is primarily sensory and comes from articular branches of the:

• Tibial nerve
• Deep fibular (peroneal) nerve
• Saphenous and sural nerves: Supply the overlying skin and contribute to periosteal sensation

Ossification

The talus ossifies from a single center of ossification, unlike many other tarsal bones. This process begins early in fetal development and is nearly complete at birth.

• Primary center appears: Around 7–8 months in utero
• Fully ossified at birth: Though secondary centers may rarely form in the posterior process (os trigonum)

Ligament Attachments

Though the talus has no muscular attachments, it is stabilized by numerous ligaments that secure it to the tibia, fibula, calcaneus, and navicular bones.

Key Ligaments

Ligament	Attachment	Function
Deltoid ligament (medial)	Medial malleolus to talus, navicular, and calcaneus	Stabilizes medial ankle, resists eversion
Anterior talofibular ligament	Lateral malleolus to neck of talus	Resists inversion and anterior translation
Posterior talofibular ligament	Fibula to posterior talus	Prevents posterior translation
Calcaneofibular ligament	Fibula to lateral calcaneus crossing talus	Stabilizes lateral ankle
Talonavicular ligament	Neck of talus to navicular	Maintains midfoot stability

Clinical Significance

• Talus fractures: Commonly involve the neck and may disrupt vascular supply, leading to avascular necrosis. Often result from dorsiflexion injuries or high-energy trauma (e.g., falls, car accidents).
• Avascular necrosis (AVN): A frequent complication after talar neck fractures, especially when blood supply through the artery of the tarsal canal is compromised.
• Talar dome lesions: Osteochondral defects from trauma or repetitive microtrauma, often presenting with chronic ankle pain and swelling.
• Os trigonum syndrome: Involves irritation or impingement of the posterior talar process or accessory bone during plantarflexion, common in ballet dancers or soccer players.
• Coalitions: Talocalcaneal coalition (fusion between talus and calcaneus) may cause limited inversion/eversion and chronic ankle pain.

Imaging

• X-ray: Standard AP, lateral, and mortise views assess alignment, fractures, and joint congruency
• CT scan: Preferred for detailed evaluation of talar fractures, comminution, and osseous coalitions
• MRI: Best for assessing AVN, talar dome lesions, bone marrow edema, and cartilage integrity
• Bone scan: May detect early AVN or delayed union post fracture