The fibula (also known as calf bone, Latin: (os) fibula) is the smaller of the bones forming the lower leg. It is located on the lateral side next to the tibia.

The fibula belongs to long bones, and it has three parts: a diaphysis or shaft, and two epiphyses or extremities - proximal and distal.

Proximal extremity of fibula

The proximal extremity or epiphysis is the upper end of the fibula, and it presents with the head of the fibula, which features an articular surface. The articular surface of the head of the fibula is the surface facing the tibia at the proximal end of the fibula.

Shaft of fibula

The diaphysis or shaft of the fibula has three surfaces (lateral, medial, posterior) and three margins (anterior, posterior, interosseous). The posterior surface features the medial crest.

The interosseous margin is a bony ridge located between the anterior margin and the medial crest of the fibula. A part of the interosseous membrane attaches to the interosseus margin of the fibula.

The medial crest is a ridge on the posterior surface of the fibula at the border between the origin sites of the tibialis posterior and the flexor hallucis longus muscles.

Distal extremity of fibula

The distal extremity or epiphysis of the fibula is the lower end of the bone, which features the lateral malleolus with a malleolar articular surface and the lateral malleolar fossa.

malleolus refers to a bony prominence on each side of the human ankle. The lateral malleolus is the prominence on the outer side of the ankle, specifically, on the distal end of the fibula. The malleolar articular surface is the surface of the lateral malleolus that faces the talus, articulating with it. The lateral malleolar fossa is a depression on the posteromedial aspect of the lateral malleolus. It serves for the attachment for the posterior talofibular ligament.