The ankle: joint structure, movements, muscles

Can you try to imagine how your walking would look like if you didn't have ankles? If this seems clumsy, imagine running without ankle... Although we often take the ankles for granted they are essential for our ability to walk, dance and drive a car.

Joint structure 
​
The ankle joint forms where the upper, inner, and outer surfaces of the talus meet the lower ends of the tibia and the fibula. It is a hinge joint capable of a specialised type of flexion (dorsiflexion) and extension (plantar flexion) in the sagittal plane. The ankle is a relatively simple structure, providing a stable link between the body and its base of support, the foot.
 
The ankle resembles a bony mortise. Medially, it is bounded by the malleolar process at the distal end of the tibia. The flat surface of the distal end of the tibia is situated superiorly and the malleolar process of the distal end of the fibula lies laterally. Distally and posteriorly stretches the smaller fibular malleolus. Anteriorly, the anterior tibiofibular ligament deepens the mortise. The posterior malleolus and the posterior tibiofibular ligament support it posteriorly. The body of the talus lies within this mortise.
 
The talus is wider in front than behind which allows a gentle side to side rocking movement during extension. That’s because in this position the narrower portion of the astragalus is in the tibiofibular socket. During flexion, on the other hand, the wider part of the talus is forced into the socket. This ‘locks’ the joint, so to speak, so that inversion and eversion of the foot can only be done through outside force.
 
It is the ankle’s sole responsibility to transmit all weight-bearing forces from the body to the foot. Perhaps due to its stability and limited degree of movement it seems immune to the degenerative changes observed in other synovial articulations.
 
The ankle is complemented by a set of accessory articulations comprising the foot. This makes it easier to cope with the stresses of daily activities and adapt to ground surface changes.

By OpenStax College [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons

​Ligaments
 
The primary ligaments of the ankle joint are the medial and the lateral.
 
The medial ligament is comprised of the deltoid ligament and the calcaneonavicular (spring) ligament.
 
The deltoid ligament’s primary role is to restrain valgus tilting of the talus. It also resists over-eversion of the foot and stabilises the ankle against pronation, external rotation, and plantarflexion. It extends from the distal part of the medial malleolus to the navicular, talus, and calcaneus bones. It is essentially four separate ligaments connecting to bones of the foot.
 
Calcaneonavicular ligament or Spring ligament stabilises statically the medial longitudinal arch and the head of the talus. It extends from the sustentaculum tali to the inferior aspect of the navicular.
 
 
The lateral ligament extends from the lateral malleolus and its primary role is to resist over-inversion. It consists of three distinct parts:
 

• From the anterior border of the lateral malleolus to the talus, in front of its lateral articular surface extends the anterior talofibular ligament.

 

• The calcaneofibular ligament stretches from the apex of the lateral malleolus to the lateral side of the calcaneus.

 

• The posterior talofibular ligament is situated between the depression on the medial and posterior aspect of the lateral malleolus in a horizontal direction to the posterior surface of the talus.

 
Some sources also include the lateral talocalcaneal and the syndesmosis (includes the anterior-inferior tibiofibular, posterior-inferior tibiofibular, transverse tibiofibular, and interosseous ligaments) as a part of the lateral ligament.
 
The described ligaments form a capsule that completely surrounds the joint.
 
There is a synovial membrane that lines the ligaments, covers the pads of fat in the joint and stretches upwards between the tibia and the fibula for a short distance.
 
There is also a number of ligaments between the bones of the foot which are beyond the scope of the present discussion. 

Movements and muscles
 
The primary movements possible at the ankle are dorsi-flexion and plantar-flexion.
 
Tibialis anterior, extensor digitorum longus, extensor hallucis longus, and peroneus tertius act together to produce dorsiflexion.
 
Plantar flexion is generated by the actions of gastrocnemius, plantaris, soleus, tibialis posterior, peroneus longus and brevis, flexor digitorum longus and flexor hallucis longus.
 
Secondary motions such as inversion, eversion and rotation are also possible.

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