Human ankle is one of the most stable joints in the human body and according to scientists; it is made to withstand a weight of more than eight times the body weight, which occurs during running. However, with all its stability and strength, the ankle joint allows the flexibility for a person to stand on their toes as well as to move the foot from side to side.
The ‘true’ and ‘subtalar’ ankle joints:
The ankle joint consists of two segments known as the ‘true ankle joint’ and the ‘subtalar’ joint. The true ankle joint is the main joint between its bones and consists of articular surfaces of the tibia, the fibulae and the talus. The tibial bone is also known as the ‘shin bone’ and is the main bony element out of the three. Parallel to the tibial bone, a smaller thin bone known as the ‘fibulae’ plays a minor role in forming the ankle joint. Both these bony elements join the horizontally arranged talus to form the ‘true ankle joint’.
Underneath the talus, it forms another joint with the ‘heel bone’ or the ‘calcaneous’. This is the joint, which is referred to as the ‘subtalar joint’ and is where the horizontal movements of the ankle take place. The true ankle joint can be described as a hinge joint as it only allows vertical movements to take place. However, in order to maintain the steadiness of these bony contacts, the ankle joint consist of many other elements which includes ligaments, muscles, articular cartilages and a joint capsule.
The articular cartilages:
The articular cartilages are arranged to cover the joint surfaces of all the bones involved. They provide the necessary strength to sustain the frictional forces taking place during movements while providing the ability to absorb shock during such movements. However, in case of injury to these cartilages, they may lose their tensile strength and may not last a lifetime as the healthy articular cartilages does.
The ligaments of the ankle joint are strong fibrous bands formed by collagen fibers. They provide stability to the joint and therefore to the movements as well. Among the major ligaments of the ankle joint, the tibio-fibular ligament provides stability from the front as it joins the tibia and the fibulae in its lower ends. The deltoid ligament provides stability from the medial side by linking up the tibia, talus and the calcaneous. The lateral collateral ligament extends from the fibulae to the calcaneous and provides lateral stability to the ankle joint.
The movements of the ankle joint is mainly done by the muscles which overlie and attach themselves to each of these bones through the tendons. Among these muscles, the calf muscle with its achillis tendon is the strongest and perhaps the most useful. It extends from the calf muscle and attaches itself to the calcaneous of the foot. The peronials, posterior tibialis and anterior tibialis are the other main muscles which override the ankle joint and supports in many ways to produce the movements that take place at this joint.
As with many other joints, the ankle joint is also encompassed in a joint capsule, which contains certain amount of fluid to lubricate the contact surfaces of each bony element.
The nerve supply to the ankle joint is mainly by the tibial nerve and there are several other nerves, which supply the region as well. Similarly, the blood supply is also through an artery known as the ‘posterior tibial artery’ with dorsalis pedis artery also contributing to a certain extent.