The ankle joint is made up of three bones: the shinbone (tibia), the smaller bone next to the shinbone (fibula) and the bone that fits into the socket formed by the tibia and the fibula (talus). The talus sits on top of the heel bone (calcaneus), forming a secondary joint. On either side of the talus is a small bony protrusion - in some people, the outer one of these lumps is naturally separated, forming a separate bone (the os trigonum).
Strong ligaments on both sides of the ankle hold the bones together - helping to stabilise the joint and to control the range of movement.
Cris-crossing the ankle joint are many tendons, which connect the muscles to the bones of the foot, enabling movement. The large Achilles tendon in the back of the ankle connects the calf muscles to the heel bone and gives the foot the power to walk, run and jump.
Inside the joint, the bones are covered with a slick, smooth material called articular cartilage, which enables smooth movement.
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