The fibula is one of two bones in the lower leg, positioned alongside the larger shin bone, the tibia. As the more slender of the two, it runs parallel to the tibia on the outer side of the leg, extending from just below the knee to the ankle. While the fibula plays a secondary role in supporting body weight compared to the tibia, it provides muscle attachment points and is necessary for ankle stability.
Anatomy and Location of the Fibula
Anatomically, the bone is divided into three main parts: the head, the shaft, and the lateral malleolus. The fibular head is the enlarged, uppermost part of the bone, located near the back of the knee. This head features a facet that articulates with the lateral condyle of the tibia, forming the proximal tibiofibular joint.
The long, slender main body is the shaft. It has a somewhat triangular shape for much of its length, providing surfaces for muscle attachments. A fibrous tissue called the interosseous membrane spans the gap between the fibula and tibia, connecting the two bones along their length and forming a syndesmosis joint. This membrane separates the muscles on the front of the leg from those in the back.
At its lower end, the fibula forms the lateral malleolus, which is the noticeable bony prominence on the outside of the ankle. The lateral malleolus articulates with the talus bone of the foot and the fibular notch of the tibia. This connection creates the distal tibiofibular joint and contributes to the structure of the ankle joint.
Key Functions of the Fibula
The fibula’s primary purpose is not weight-bearing, though it supports about 17% of the body’s load. Its main functions are muscle attachment and joint stability. The shaft of the fibula serves as an anchor point for numerous muscles that control movements in the foot and ankle. These muscles are responsible for actions such as pointing the foot downwards (plantar flexion) and turning it outwards (eversion).
The bone’s role in the ankle is notable. The lateral malleolus, which forms the outer ankle bone, acts as a pulley for tendons and is a site for ligament attachments. These ligaments provide stability to the ankle joint, preventing it from moving excessively. By forming the outer part of the ankle mortise—the socket that the talus bone fits into—the lateral malleolus is integral to the mechanical function of the ankle during activities like walking and running.
Common Fibular Injuries and Symptoms
Fractures are the most frequent type of injury to the fibula. These can occur from direct blows to the leg but are more often associated with twisting ankle injuries. A forceful roll of the ankle can cause a break in the lateral malleolus, a common type of fibular fracture. Other types include stress fractures from repetitive strain in sports, and avulsion fractures, where a tendon or ligament pulls off a piece of bone.
Symptoms of a fibular fracture include immediate and sharp pain at the site of the injury. Swelling, bruising, and tenderness over the bone often appear shortly after the incident. Depending on the severity and location of the break, it may be difficult or impossible to put weight on the affected leg. A visible deformity may also be present if the bones are significantly displaced.
Diagnosing and Treating Fibular Issues
A medical diagnosis begins with a physical examination and a review of how the injury occurred. A healthcare provider will assess for swelling, bruising, and tenderness along the bone. To confirm a fracture and determine its location and severity, an X-ray is the standard imaging tool. For complex injuries with significant ligament damage or multiple fractures, a CT scan or MRI may be ordered.
Treatment for a fibular fracture depends on whether the bone fragments are displaced and the ankle joint is stable. Many fractures can be managed conservatively without surgery, involving immobilization with a cast, splint, or walking boot to allow the bone to heal. The RICE protocol—Rest, Ice, Compression, and Elevation—is also recommended to manage pain and swelling.
For more severe fractures where the bones are out of alignment or the ankle joint is unstable, surgery may be required. A common surgical procedure is an open reduction and internal fixation (ORIF), where a surgeon realigns the bone fragments and secures them with plates and screws. Following treatment, physical therapy is used to restore strength, flexibility, and function to the leg and ankle.