Corpus: Ankle joint

The term ankle joint refers to the main joint of the foot, which consists of two component joints: the talocrural joint and the talotarsal joint. Functionally, the ankle joint combines the characteristics of a hinge joint and a ball-and-socket joint.

2.1. Talocrural joint

The talocrural joint connects the lower leg bones (tibia and fibula) to the talus. It functions as a pure hinge joint. The joint socket is formed by the malleolar fork, which includes the medial malleolus of the tibia and the lateral malleolus of the fibula. The joint head is formed by the trochlea of talus.

2.2. Talotarsal joint

The talotarsal joint combines features of a pivot joint and a ball-and-socket joint. It is made up of two smaller joints.

2.2.1. Anterior talotarsal joint

The anterior talotarsal joint (also called talocalcaneonavicular joint) is formed by the talus (joint head) and the calcaneus, navicular bone, and the plantar calcaneonavicular ligament (joint socket).

2.2.2. Posterior talotarsal joint

The posterior talotarsal joint (also called subtalar joint) is made up of the concave surface of the talus and the convex surface of the calcaneus.

3.1. Talocrural joint

The talocrural joint's capsule is relatively thin and attaches to the cartilage-bone boundaries of the tibia and fibula, as well as to the neck of the talus. The malleoli lie outside the joint capsule. The capsule is reinforced by several ligaments:

• Medial Side: The deltoid ligament (also called the medial collateral ligament) is a strong, fan-shaped ligament that extends from the medial malleolus to the tarsal bones (talus, calcaneus and navicular bone). It is made up of four parts (tibionavicular, tibiocalcaneal, anterior tibiotalar and posterior tibiotalar part).
• Lateral Side, extending from the lateral malleolus to the tarsal bones:
  • Anterior talofibular ligament
  • Posterior talofibular ligament
  • Calcaneofibular ligament

These three ligaments are often summarised as the lateral collateral ligament.

3.2. Talotarsal joint

The talotarsal joint contains two separate chambers with distinct joint capsules, which are attached to the periphery of the joint surfaces. Several ligaments help reinforce these capsules:

• Deltoid ligament (tibiocalcaneal and tibionavicular parts): Limits pronation
• Calcaneofibular ligament: Limits supination
• Interosseous talocalcaneal ligament: Separates the two parts of the talotarsal joint
• Medial talocalcaneal ligament
• Lateral talocalcaneal ligament
• Posterior talocalcaneal ligament
• Talonavicular ligament: Connects the talus to the navicular bone
• Long plantar ligament: A broad ligament running from the plantar surface of the calcaneus to the cuboid bone and the bases of the metatarsals

The talocrural joint allows the following movements:

• Dorsiflexion (extension) of the foot: up to 20°
• Plantar flexion of the foot: up to 30°

The talotarsal joint enables the following movements:

• Supination (lifting of the medial edge of the foot while lowering the lateral edge): up to 50°
• Pronation (lifting of the lateral edge of the foot while lowering the medial edge): up to 30°
• Inversion (combination of supination, plantar flexion and adduction)
• Eversion (combination of pronation, dorsiflexion and abduction)

Proprioception in the ankle joint relies on mechanoreceptors in the ligaments and muscle spindles in the lower leg muscles. The central nervous system interprets the tension in the ligaments and muscles to determine the joint's position, which is crucial for maintaining balance.

The ankle joint is prone to injuries due to its exposed position and the significant forces it endures. Common injuries include damage to the ligaments, such as sprains or tears, which are collectively referred to as ankle sprains. Other potential injuries include:

• Ankle fractures
• Ankle dislocations

In cases of supination trauma, the anterior talofibular ligament is most frequently injured.

Diagnosis of ankle injuries is based on clinical examination, as well as imaging techniques like ultrasound and X-rays.