The distal fibula, a slender bone in the lower leg, plays an important role in the stability and function of the ankle joint. It runs parallel to the larger tibia, or shinbone, on the outer side of the leg. This bone helps form the structure of the calf and is a component of the ankle’s articulation. Understanding the distal fibula’s structure and purpose helps comprehend its susceptibility to injury.
Anatomy and Location
The fibula is a long bone, thinner and smaller than the tibia, positioned on the lateral (outer) side of the lower leg. Its distal, or lower, end articulates with both the tibia and the talus bone of the foot. This lower portion extends downward to form the lateral malleolus, the prominent bony bump felt on the outside of the ankle.
The fibula connects to the tibia along its length via an interosseous membrane, a sheet of connective tissue that forms a syndesmotic joint with limited mobility. At its distal end, the fibula also forms the distal tibiofibular joint with the tibia, fitting into a depression called the fibular notch.
Function
The distal fibula stabilizes the ankle joint, acting as a lateral stabilizer. It combines with the tibia to form the ankle mortise, a socket that securely holds the talus bone. This mortise structure is important for guiding ankle movements like dorsiflexion and plantarflexion.
The distal fibula also serves as an attachment site for several ligaments that stabilize the ankle. These include the anterior inferior tibiofibular ligament (AITFL), posterior inferior tibiofibular ligament (PITFL), and the interosseous ligament, which are important for syndesmosis stability. The lateral collateral ligaments, such as the anterior talofibular ligament (ATFL) and calcaneofibular ligament (CFL), originate from the lateral malleolus, resisting excessive inversion and rotation of the ankle. The fibula’s structural integrity is important for proper ankle biomechanics.
Common Injuries
The distal fibula is often injured due to its role in ankle stability and movement. Fractures of the distal fibula are common, often occurring from twisting motions, direct impact, or falls. These fractures are classified based on their location relative to the syndesmosis, using systems like the Weber classification (A, B, or C).
Weber A fractures occur below the syndesmosis and are stable, often resulting from inversion injuries where the foot turns inward. Weber B fractures happen at the level of the syndesmosis, indicating potential instability. Weber C fractures are located above the syndesmosis and usually signify an unstable injury often requiring surgical intervention. A Maisonneuve fracture involves a proximal fibula fracture combined with an unstable ankle injury, including damage to syndesmotic ligaments and often the medial malleolus or deltoid ligament. This type of fracture commonly results from an external rotation force applied to the ankle.
Beyond fractures, the ligaments attaching to the distal fibula are susceptible to sprains, particularly the lateral ankle ligaments. Ankle sprains, especially inversion injuries, can stretch or tear these ligaments, such as the ATFL and CFL. A “high ankle sprain,” or syndesmotic injury, involves damage to the ligaments connecting the tibia and fibula above the ankle, like the AITFL and PITFL, and often results from external rotation or forceful dorsiflexion. These injuries can lead to significant pain, swelling, bruising, and difficulty bearing weight.
Diagnosis and Treatment
Diagnosing issues with the distal fibula begins with a physical examination, where a healthcare provider assesses pain, swelling, and range of motion. Imaging confirms the diagnosis and extent of injury. X-rays are the first line of imaging, providing views to identify fracture alignment and displacement. Weight-bearing X-rays or stress views may be used to evaluate ankle stability and detect syndesmotic injuries. More detailed imaging, such as an MRI, can provide comprehensive views of bones and surrounding soft tissues, including ligaments, for complex injuries or when X-rays are inconclusive.
Treatment approaches for distal fibula injuries vary depending on the type and severity of the injury. Non-surgical management is often effective for stable, non-displaced fractures and mild to moderate sprains. This conservative approach involves the RICE method (Rest, Ice, Compression, and Elevation) to reduce swelling and pain. Immobilization with a cast, walking boot, or brace helps protect the injured area and promote healing, for a period of 4 to 6 weeks. Physical therapy often follows immobilization, focusing on restoring ankle range of motion, strength, and balance.
Surgical intervention becomes necessary for unstable or significantly displaced fractures, as well as for severe ligamentous injuries that compromise ankle stability. Procedures like Open Reduction and Internal Fixation (ORIF) use plates and screws to realign and stabilize bone fragments. For Maisonneuve fractures, surgery often involves inserting screws to stabilize the ankle joint while ligaments heal. Post-surgical care includes a period of non-weight bearing, followed by gradual progression to weight-bearing and a structured physical therapy program to regain full function.