The ankle joint consists of an articulation between the tibia, fibula and talus. It is a hinge type synovial joint, allowing dorsiflexion and plantarflexion.
The Articulating Surfaces of the Ankle Joint
The tibia and fibula are bound distally by strong tibiofibular ligaments. The malleoli of the tibula and fibula produce a bracket shaped socket, called a mortise.
The talus bone has an expanded upper part for articulation with the leg bones. The articulating surface of the talus is wider anteriorly and thinner posteriorly. This is significant; during dorsiflexion of the foot, the wider articulating surface moves into the joint, and it is held snugly. During plantarflexion, the thinner articulating surface moves into the joint, and the fit is less tight, thus the joint is weaker. More injuries occur to the ankle joint when it is plantarflexed.
Ligaments of the Ankle Joint
There are two sets of ligaments, one originating from each malleolus. They act to stablise the ankle joint.
Medial ligament – this ligament reinforces the joint on the medial side. It is also called the deltoid ligament, as it is triangular in shape. It consists of four separate ligaments, which fan out from the medial malleolus. It resists over-eversion of the foot.
The lateral ligament resists inversion of the foot, and resists over-inversion of the foot. It is comprised of three separate ligaments:
- Posterior talofibular
- Anterior talofibular
Clinical Relevance: The Ankle Ring
The ankle can be thought of as a ring in the coronal plane. The upper part is formed by the articular surfaces of the tibia and fibula, the lower part is formed by the subtalar joint (between the talus and the calcaneus). The medial and lateral sides of the ring are formed by the medial and lateral ligaments.
When a ring breaks, it usually does so in two locations. So when dealing with an injury to the ankle joint, a clinician must bear this in mind. For example, a fracture in one location on the ‘ring’ may cause damage to the ligaments in another area – which would not show up on x-ray.
Movements of the Ankle Joint and the Muscles Involved
Plantarflexion and dorsiflexion are the main movements that occur at the ankle joint. A small amount of ‘wobble’ can occur, which is able to produce adduction, abduction, inversion and eversion.
Plantarflexion – produced by the muscles in the posterior compartment of the leg; gastrocnemius, soleus, plantaris and posterior tibialis.
Dorsiflexion – produced by the muscles in the anterior compartment of the leg; tibialis anterior, extensor hallucis longus and extensor digitorum longus.
Clinical Relevance: Common Conditions Affecting the Joint
A sprain of the ankle is the most common injury to this joint, and almost always by forced inversion of a plantarflexed, weight bearing foot. The lateral ligament is most often damaged, this is because of two reasons:
1) The lateral ligament is weaker than the medial ligament
2) The lateral ligament resists inversion
The anterior talofibular ligament is the lateral ligament most at risk of irreversible damage.
This injury occurs when the foot is everted, and occurs in a series of stages:
1) Forced eversion pulls on the medial ligaments, will causes an avulsion fracture of the medial malleolus
2) The talus moves laterally, breaking off the lateral malleolus, or causing a fracture of the fibula above the tibiofibular joint.
3) If the tibia is pushed anteriorly, the talus shears off the distal, proximal portion.
Other Joints of the Foot
There are many joints in the foot, but the three main ones are the subtalar, talocalcaneonavicular and calcaneocuboid joints. These joints allow for inversion and eversion of the foot to occur.
The talocalcaneonavicular and calcaneocuboid joints are sometimes referred to as a collective joint, the transverse tarsal joint.
Subtalar – articulation between the inferior surface of the talus and the superior surface of the calcaneus
Talocalneonavicular - articulation between the talus, the calcaneus and navicular
Calcaneocuboid – articulation between the calcaneus and the cuboid