Although it is typically referred to as a single joint, the ankle is actually two joints:
The true ankle joint, which is composed of three bones:
- the tibia, the larger and stronger of the two lower leg bones, which forms the inside part of the of the ankle
- the fibula, the smaller bone of the lower leg, which forms the outside part of the ankle
- the talus, a small bone between the tibia and fibula and the calcaneus, or heel bone.
The subtalar joint, which is composed of two bones:
- the talus
- the calcaneus
The ends of the bones are covered by articular cartilage. The space in the joint is lined with a thin membrane called the synovium, which cushions the joint and secretes a lubricating fluid, called synovial fluid.
Several strong bands of connective tissue, called ligaments, hold the bones of the ankles together. They include the following:
- anterior tibiofibular ligament, which connects the tibia to the fibula
- lateral collateral ligaments, which connect the fibula to the calcaneus and provide stability to the outsides of the ankles
- deltoid ligaments, which attach the tibia to the talus and calcaneus and provide stability to the insides of the ankles
A number of tendons run through the ankle, attaching muscles of the lower leg to the bones of the foot and ankle. The major tendons include the following:
- Achilles tendon, which attaches the calf muscle and calcaneus
- flexor hallicus longus, which runs along the inside of the ankle and attaches to the big toe
- flexor digitorum, which runs along the inside of the ankle and attaches to the other toes
- peroneal tendons, a set of three tendons which run along the outside of the ankle and attach at the 5th metatarsal (the shaft of the small toe) and the bottom of the foot
- posterior tibialis tendon, which attaches at the mid-foot and helps maintain the foot's arch
- anterior tibialis tendon, which runs down the front of the leg and attaches to the bones of the midfoot. These tendons pull the foot toward the body and help control their motion.