The ankle is a very complex joint. When everything works together, the ankle function correctly. But, if one part becomes damaged, it can affect other parts of the foot and ankle, leading to problems. The unique design of the ankle makes it a very stable joint. This is important because it must withstand 1.5x your body weight when you walk and up to 8x your body weight with running. The ankle acts like a hinge, but it is much more complex than just a simple hinge. The ankle functions to help propel the body with a smooth and nearly effortless gait.
The ankle joint is actually made up of two joints: the true ankle joint and the subtalar joint. The true ankle joint is formed by the connection of three bones: the talus, the tibia (shinbone) and the fibula (smaller bone on the outside of the lower leg). The top of the talus sits in a socket formed by the end of the tibia and the fibula. This acts like a hinge allowing your foot to move up and down. The subtalar joint sits beneath the true ankle joint. It consists of the talus on top and the calcaneus (heel bone) on the bottom. The subtalar joint allows side-to-side motion of the foot.
Articular cartilage covers the ends of bones in all joints. It is a white, shiny material that is about a quarter of an inch thick in the ankle. In the ankle, this durable material covers the ends of the tibia, fibula, talus, and calcaneus bones. It allows the surfaces to glide over one another aiding in motion as well as allowing for shock absorption for weight bearing.
Ligaments are strong bands of tissue that connect bone to bone. The ligaments on either side of the ankle joint help hold the bones together. The lateral ligament complex, on the outside of the ankle, is made up of three major ligaments. These are the anterior talofibular ligament (ATFL), the calcaneofibular ligament (CFL) and the posterior talofibular ligament (PTFL). On the inside of the ankle, the deltoid ligament provides medial stability to the ankle.
Ligaments also support the end of the lower leg between the tibia and fibula. This set of ligaments is called the syndesmosis. A long sheet of connective tissue, called the interosseous ligament, lies between the tibia and fibula along their entire length from the ankle to the knee. This also aids with stability of the lower leg. The joint capsule is a watertight sac that surrounds all joints. It is made up of the ligaments and soft tissue that surround the ankle joint.
The muscles of the lower leg whose tendons pass the ankle and connect to the foot cause most of the motion of the ankle. Nearby tendons also help support the ankle joint. The achilles tendon is an important tendon for walking, running and jumping. It attaches the calf muscles to the calcaneus and helps us go up on our toes or push-off with our feet. The anterior tibial tendon in front of the ankle raises the foot upward. The posterior tibial tendon helps support the arch and turns the foot inward. The two tendons that run behind the smaller bone on the outside of the ankle, the peroneal tendons, help push the foot down and rotate outward.
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