The bony architecture of the ankle consists of three bones: the tibia, the fibula, and the talus. The articular surface of the tibia is referred to as the plafond. The medial malleolus is a bony process extending distally off the medial tibia. The distal-most aspect of the fibula is called the lateral malleolus. Together, the malleoli, along with their supporting ligaments, stabilize the talus underneath the tibia.
The bony arch formed by the tibial plafond and the two malleoli is referred to as the ankle "mortise" (or talar mortise). The mortise is a rectangular socket. The ankle is composed of three joints: the talocrural joint (also called talotibial joint, tibiotalar joint, talar mortise, talar joint), the subtalar joint (also called talocalcaneal), and the Inferior tibiofibular joint. The joint surface of all bones in the ankle are covered with articular cartilage.
The distances between the bones in the ankle are as follows:
- Talus - medial malleolus : 1.70 ± 0.13 mm
- Talus - tibial plafond: 2.04 ± 0.29 mm
- Talus - lateral malleolus: 2.13 ± 0.20 mm
Decreased distances indicate osteoarthritis.
- The deltoid ligament supports the medial side of the joint, and is attached at the medial malleolus of the tibia and connect in four places to the talar shelf of the calcaneus, calcaneonavicular ligament, the navicular tuberosity, and to the medial surface of the talus.
- The anterior and posterior talofibular ligaments support the lateral side of the joint from the lateral malleolus of the fibula to the dorsal and ventral ends of the talus.
- The calcaneofibular ligament is attached at the lateral malleolus and to the lateral surface of the calcaneus.
Though it does not span across the ankle joint itself, the syndesmotic ligament makes an important contribution to the stability of the ankle. This ligament spans the syndesmosis, i.e. the articulation between the medial aspect of the distal fibula and the lateral aspect of the distal tibia. An isolated injury to this ligament is often called a high ankle sprain.
The bony architecture of the ankle joint is most stable in dorsiflexion. Thus, a sprained ankle is more likely to occur when the ankle is plantar-flexed, as ligamentous support is more important in this position. The classic ankle sprain involves the anterior talofibular ligament (ATFL), which is also the most commonly injured ligament during inversion sprains. Another ligament that can be injured in a severe ankle sprain is the calcaneofibular ligament.
Mechanoreceptors of the ankle send proprioceptive sensory input to the central nervous system (CNS). Muscle spindles are thought to be the main type of mechanoreceptor responsible for proprioceptive attributes from the ankle. The muscle spindle gives feedback to the CNS system on the current length of the muscle it innervates and to any change in length that occurs.
It was hypothesized that muscle spindle feedback from the ankle dorsiflexors played the most substantial role in proprioception relative to other muscular receptors that cross at the ankle joint. However, due to the multi-planar range of motion at the ankle joint there is not one group of muscles that is responsible for this. This helps to explain the relationship between the ankle and balance.
In 2011, a relationship between proprioception of the ankle and balance performance was seen in the CNS. This was done by using a fMRI machine in order to see the changes in brain activity when the receptors of the ankle are stimulated. This implicates the ankle directly with the ability to balance. Further research is needed in order to see to what extent does the ankle affect balance.
- Trochlea of Talus
- Malleolar Mortis formed by Tibia & Fibula
- Lateral & Medial Malleolus
The Joint Capsule
The articular capsule surrounds the joints, and is attached, above, to the borders of the articular surfaces of the tibia and malleoli; and below, to the talus around its upper articular surface. The joint capsule anteriorly is a broad, thin, fibrous layer, posteriorly the fibres are thin and run mainly transversly blending with the transverse ligamanet and laterally the capsule is thickened, and attaches to the hollow on the medial surface of the lateral malleolus. The synovial membrane extends superiorly between Tibia & Fibula as far as the Interosseous Tibiofibular Ligament.
Foot and Ankle Orthopedic Evaluation
Lower Extremity ROM Norms
Range of Motion
Ankle Joint Play
Lower Extremity Cutaneous Innervation
Other Great Ankle Resources
Return to Play in Athletes Following Ankle Injuries - Return to Sport