The lateral malleolus is the prominent, bony knob located on the outside of the ankle joint. This structure is easily felt beneath the skin and functions as a protective shield for the ankle. It represents the lower, flared end of the smaller calf bone, known as the fibula, and is a foundational part of the entire ankle complex.
Anatomy and Location
The lateral malleolus forms the distal-most extension of the fibula, the slender bone running parallel to the tibia in the lower leg. It is shaped somewhat like a shield, extending further downward and slightly more posterior than the medial malleolus on the inner ankle. This unique positioning helps to stabilize the ankle joint. The malleolus provides a rough, textured surface that serves as the attachment point for the lateral collateral ligaments of the ankle. These strong, fibrous bands connect the fibula to the talus and calcaneus bones of the foot, forming a sturdy structural network.
Role in Ankle Stability
The function of the lateral malleolus is to contribute to the stability of the ankle joint, which is formally called the talocrural joint. Together with the medial malleolus of the tibia, it creates a secure, bracket-shaped socket, or “mortise,” that holds the talus bone firmly in place. This bony architecture limits the side-to-side motion of the talus, ensuring the ankle mainly performs hinge-like movements. The lateral malleolus acts as a mechanical block, preventing the foot from rolling too far inward, a motion known as excessive inversion.
Ligamentous Support
Attached to its surfaces are the three main lateral ligaments—the anterior talofibular, calcaneofibular, and posterior talofibular ligaments—which provide static support and stabilize against inversion stress.
Common Injuries to the Lateral Malleolus
Since it bears the brunt of forces attempting to roll the ankle, the lateral malleolus is frequently involved in injuries, primarily through two mechanisms: fracture and ligament sprain.
Fractures
A lateral malleolus fracture is a break in the distal end of the fibula, commonly caused by a forceful twisting motion or direct impact. These breaks are among the most common types of ankle fractures. The stability of the entire ankle joint depends on whether the fracture has disrupted the surrounding ligamentous structures and the alignment of the talus within the mortise.
Sprains
The ligaments that anchor to the lateral malleolus are highly susceptible to injury, leading to ankle sprains. When the foot rolls inward, these lateral collateral ligaments are stretched or torn, which is the most common mechanism for an ankle sprain. A severe sprain, classified as Grade 2 or Grade 3, involves a partial or complete tear of one or more of these ligaments, most often the anterior talofibular ligament. This ligament damage compromises the stabilizing role of the malleolus, resulting in pain, swelling, and instability.
Diagnosis and Initial Management
Following an injury, diagnosis typically begins with a physical examination to check for localized tenderness and the ability to bear weight. Imaging is usually required to differentiate between a soft tissue sprain and a bone fracture, which can present with similar symptoms. Standard three-view X-rays of the ankle are the first-line imaging choice, often guided by clinical rules. If a fracture is confirmed, the medical team will assess the stability of the ankle joint, sometimes using stress X-rays to check for abnormal widening of the joint space.
Initial Management
Initial management for nearly all acute ankle injuries involves the R.I.C.E. protocol: Rest, Ice, Compression, and Elevation. Rest limits further damage, while ice, compression, and elevation help to control swelling and pain. Seeking a prompt medical evaluation is important, especially if the pain is severe or if the individual is unable to walk even a few steps, which can suggest a more serious fracture or unstable injury.