The malleolus refers to the prominent bony projections found on either side of the ankle. These distinct structures are an integral part of the ankle joint, playing a significant role in its stability and movement. This article clarifies their location and importance.
Identifying the Malleolus
The ankle features two primary malleoli, easily felt as distinct “knobs” on either side. The medial malleolus is the bony projection on the inner side of the ankle. It is the lower, flared end of the tibia, the larger lower leg bone (shin bone). This medial prominence articulates with the talus, a foot bone.
The lateral malleolus is the bony prominence on the outer side of the ankle. It is formed by the distal end of the fibula, the thinner bone parallel to the tibia. The lateral malleolus extends lower than the medial malleolus and also articulates with the talus. These two malleoli, with the lower tibia, create a socket-like structure called the ankle mortise, where the talus fits snugly.
A third, less prominent malleolus, the posterior malleolus, is at the back of the ankle. This projection is also part of the tibia. Though not as easily palpable as the medial and lateral malleoli, it contributes to the ankle joint’s overall structure. All three malleoli are the expanded, distal ends of the tibia and fibula, forming the ankle’s crucial articulations.
Role in Ankle Function
The malleoli and talus form the talocrural joint, commonly known as the ankle joint. This joint functions as a hinge, allowing two main movements: dorsiflexion (pointing the foot upwards) and plantarflexion (pointing the foot downwards, like pressing a gas pedal).
Beyond movement, the malleoli provide stability to the ankle joint. Their shape and position create a bony enclosure preventing excessive side-to-side movement of the talus within the ankle mortise. Strong ligaments attach to these bony prominences, reinforcing the joint and limiting unnatural motion. This structural arrangement ensures the ankle can bear body weight and withstand forces during activities like walking, running, and jumping.
Common Injuries
The malleoli are often involved in ankle injuries, especially fractures. Malleolar fractures are breaks in one or more of these bony prominences. An injury affecting only one malleolus is a unimalleolar fracture; lateral malleolus fractures are the most common. If both the medial and lateral malleoli are fractured, it is a bimalleolar fracture.
In severe cases, all three malleoli—medial, lateral, and posterior—can be fractured, resulting in a trimalleolar fracture. These fractures often occur due to twisting injuries or direct trauma, such as falls. While the malleoli are bones, severe ankle sprains can sometimes cause small avulsion fractures. This occurs when a ligament pulls a tiny piece of bone away from the malleolus at its attachment point. Any suspected ankle injury requires prompt medical evaluation for proper diagnosis and treatment.