The fibula, often called the calf bone, is one of the two bones forming the lower leg, situated alongside the larger tibia. Despite its slender appearance, the fibula plays several important roles in the leg’s overall function and stability. Its contributions are essential for movement and maintaining the integrity of the ankle joint.
Anatomical Positioning
The fibula is located on the lateral aspect of the lower leg, running parallel to the tibia. It extends from just below the knee down to the ankle. Its structure includes a head at the top, a long shaft, and a distal end that forms part of the ankle.
At its upper end, the fibula’s head articulates with the lateral condyle of the tibia, forming the proximal tibiofibular joint. A fibrous interosseous membrane connects the fibula to the tibia along much of their length, providing stability. At the ankle, the fibula’s distal end forms the lateral malleolus, the bony prominence on the outer side of the ankle. This articulates with the talus bone of the foot, contributing to the ankle joint. Unlike the tibia, the fibula does not bear a substantial amount of the body’s weight, typically carrying only about 5-17% of the load.
Primary Contributions to Leg Function
The fibula’s functions contribute to the mechanics and stability of the lower leg and foot. A primary role is providing stability to the ankle joint. The lateral malleolus, formed by the fibula’s distal end, creates the outer boundary of the ankle mortise, preventing excessive outward rolling of the foot, known as eversion. Several strong ligaments, including the anterior talofibular, posterior talofibular, and calcaneofibular ligaments, attach to the lateral malleolus, reinforcing ankle stability.
The fibula also serves as an attachment site for numerous muscles in the lower leg. Muscles such as the fibularis longus and fibularis brevis (peroneal muscles) originate from the fibula. These muscles are responsible for movements like eversion of the foot (turning the sole outward) and plantarflexion (pointing the toes downward). Other muscles, including some calf muscles, also attach to the fibula, enabling diverse foot and ankle movements essential for walking, running, and maintaining balance, while also offering some protection for the nerves and blood vessels that run alongside it in the lower leg.
Impact of Fibula Impairment
When the fibula’s functions are compromised, typically through injury, issues can arise, impacting mobility and stability. Fractures of the lateral malleolus, the most common type of ankle fracture, can destabilize the ankle joint. Such injuries often lead to immediate pain, swelling, bruising, and difficulty bearing weight or walking. The extent of instability depends on the fracture’s location and whether associated ligaments are also damaged.
Injuries to the upper part of the fibula, particularly near its neck, can affect the common fibular nerve (common peroneal nerve), which wraps around this area. Damage to this nerve can result in foot drop, where an individual has difficulty lifting the front part of the foot, causing it to drag during walking. This impairment highlights the fibula’s relationship with nerve pathways.
Fibula injuries can also disrupt the attachment points for the muscles originating from it, leading to weakness or impaired movement of the foot and ankle. For example, damage affecting the peroneal muscles can compromise the ability to evert the foot or maintain proper ankle stability during movement. Recovering from fibula impairment often involves rehabilitation, including physical therapy, to restore strength, flexibility, and balance. The fibula’s functions are interconnected with overall lower limb mobility, making its proper healing important for regaining full function.