Malleolus (Latin, "small hammer") is the bony prominence on each side of the ankle.
Each leg is supported by two bones, the tibia on the inner side (medial) of the leg and the fibula on the outer side (lateral) of the leg. The medial malleolus is the prominence on the inner side of the ankle, formed by the lower end of the tibia. The lateral malleolus is the prominence on the outer side of the ankle, formed by the lower end of the fibula.
The summit of the medial malleolus is marked by a rough depression behind, for the attachment of the deltoid ligament.
Structures that pass behind medial malleolus deep to flexor retinaculum:
Tibialis posterior tendon
Flexor digitorum longus
Posterior tibial artery
Posterior tibial vein
Flexor hallucis longus
The lower extremity of the fibula, also called the distal extremity or external malleolus, is of a pyramidal form and somewhat flattened from side to side; it descends to a lower level than the medial malleolus.
The medial surface presents in front a smooth triangular surface, convex from above downward, which articulates with a corresponding surface on the lateral side of the talus. Behind and beneath the articular surface is a rough depression, which gives attachment to the posterior talofibular ligament.
The lateral surface is convex, subcutaneous, and continuous with the triangular, subcutaneous surface on the lateral side of the body.