Fibula anatomy: the slender lateral bone of the leg

What it is

The slender lateral bone of the leg.

Location

Lies lateral to the tibia, articulating with it at the proximal and distal tibiofibular joints and forming the lateral malleolus.

Function

Provides muscle attachment and stabilises the ankle joint; it bears little weight.

Body system

Skeletal · paired (left and right)

FMA ID

FMA24481 (Foundational Model of Anatomy)

Key facts

• The common fibular nerve winds around its neck.
• Biceps femoris and the lateral (fibular) collateral ligament attach to its head.
• Its lateral malleolus reaches further down and lies further back than the medial malleolus.

Clinical relevance

Injury to the common fibular nerve at the fibular neck can cause foot drop.

The fibula lies lateral to the tibia in the leg, between the knee and the ankle. It is thin and does not bear weight, so it serves mainly for muscle attachment. Only its upper and lower ends can be felt through the skin: the head just below the outer side of the knee, and the lateral malleolus at the outer ankle. (OpenStax Anatomy and Physiology 2e, 8.4: Bones of the Lower Limb.)

The fibula articulates with the tibia above at the proximal tibiofibular joint, with the tibia below at the distal tibiofibular joint, and with the talus at the ankle joint. It does not form part of the knee joint itself. (TeachMeAnatomy: The Fibula.)

The head of the fibula is the knob-like upper end. A flat facet on its medial side meets the underside of the lateral condyle of the tibia at the proximal tibiofibular joint. The apex (styloid process) projects upwards from the back and outer part of the head; the fibular (lateral) collateral ligament of the knee attaches here and is wrapped by the tendon of biceps femoris. (Kenhub: Fibula.)

The neck is the short, narrow part below the head. The common fibular (common peroneal) nerve winds around its posterolateral side before dividing into its branches, so injuries at this level can damage it. (TeachMeAnatomy: The Fibula.)

The shaft is triangular in cross-section, with anterior, interosseous and posterior borders and medial, lateral and posterior surfaces. Muscles that dorsiflex the foot arise from the medial surface, the fibularis (peroneal) muscles from the lateral surface, and muscles that plantarflex the foot from the posterior surface. A nutrient foramen on the posterior surface, a few centimetres above the midpoint, admits a branch of the fibular artery, which supplies the bone. (Kenhub: Fibula.)

Fibularis (peroneus) longus arises from the upper lateral fibula and fibularis (peroneus) brevis from the lower lateral shaft. Both tendons pass behind the lateral malleolus: longus crosses the sole to the medial cuneiform and base of the first metatarsal, while brevis inserts on the tubercle of the fifth metatarsal. Both are supplied by the superficial fibular nerve. (TeachMeAnatomy: Muscles in the Lateral Compartment of the Leg.)

The distal end of the fibula forms the lateral malleolus, the bony bump on the outer side of the ankle. Its medial surface articulates with the talus, and just above that it fits into the fibular notch of the tibia at the distal tibiofibular joint. (OpenStax Anatomy and Physiology 2e, 8.4: Bones of the Lower Limb.)

The lateral malleolus is more prominent than the medial malleolus of the tibia and is easy to palpate on the outer side of the ankle. (TeachMeAnatomy: The Fibula.)

Through the distal tibiofibular joint, the lower fibula contributes to the ankle mortise, the socket that holds the talus. Ankle ligaments attached to the distal fibula include the posterior talofibular and calcaneofibular ligaments, together with the posterior and interosseous tibiofibular ligaments of the syndesmosis. A broad groove marks the back of the malleolus. (Kenhub: Fibula.)

The proximal (superior) tibiofibular joint is a plane synovial joint between the fibular head and the lateral tibial condyle. Its capsule is reinforced by the anterior and posterior superior tibiofibular ligaments (ligaments of the fibular head) and supported by the lateral collateral ligament and the biceps femoris tendon. It is supplied by the inferior genicular and anterior tibial recurrent arteries and innervated by branches of the common fibular nerve and the nerve to popliteus. (TeachMeAnatomy: The Tibiofibular Joints.)

The middle tibiofibular joint is the interosseous membrane, which connects the shafts of the two bones along their length. (Kenhub: Tibiofibular joints.)

The distal (inferior) tibiofibular joint is a syndesmosis, a fibrous joint between the convex medial surface of the lower fibula and the concave fibular notch of the tibia. It has no capsule of its own. Four ligaments hold it: the interosseous tibiofibular ligament (the main stabiliser, continuous with the interosseous membrane), the anterior tibiofibular ligament, the thicker and wider posterior tibiofibular ligament, and the inferior transverse tibiofibular ligament, which many authors treat as part of the posterior ligament. (Kenhub: Tibiofibular joints.)

The anterior and posterior ligaments of the distal joint are often called the anterior inferior tibiofibular ligament (AITFL) and posterior inferior tibiofibular ligament (PITFL), to separate them from the superior ligaments at the knee end; the inferior transverse tibiofibular ligament continues on from the posterior one. Being fibrous, the distal joint has no joint capsule. It receives blood from branches of the fibular artery and the anterior and posterior tibial arteries. (TeachMeAnatomy: The Tibiofibular Joints.)

The distal joint allows only small movements. In dorsiflexion the fibula moves up and rotates outwards a little, slightly widening the space between the bones to accommodate the talus; in plantarflexion it glides down and the space narrows. (Kenhub: Tibiofibular joints.)

The fibular shaft starts to ossify around the 8th week of gestation. A centre for the distal end appears by the end of the first year, and one for the proximal end at about 3 years in girls and 4 in boys. The distal centre fuses with the shaft in mid-adolescence (about 15 in females, 17 in males) and the proximal centre last (about 17 in females, 19 in males). (Kenhub: Fibula.)

The fibula is the thin lateral bone and the tibia the thick medial one. The tibia carries body weight from the knee to the ankle, while the fibula mainly anchors muscles. Each ends at the ankle in a malleolus: the medial malleolus belongs to the tibia and the lateral malleolus to the fibula. (OpenStax Anatomy and Physiology 2e, 8.4: Bones of the Lower Limb.)

Fibular fractures usually come with a tibial fracture or an ankle injury; isolated fractures are less common because the tibia takes most of the load. Rotational forces produce spiral fractures, while angular forces give transverse or oblique ones. Stress fractures are relatively common in military recruits and athletes, most often in the distal third. (Kenhub: Fibula.)

The lateral malleolus is a common fracture site. Forced external rotation of the foot drives the talus against it and typically causes a spiral fracture; less often, forced eversion pulls off a fragment as a transverse avulsion fracture. (TeachMeAnatomy: The Fibula.)

Distal fibular fractures are graded with the Weber (Danis-Weber) classification, types A, B and C, by the level of the fracture. A Maisonneuve fracture combines a fracture of the proximal fibula with injury at the medial malleolus and disruption of the distal tibiofibular syndesmosis. Proximal fibular fractures can damage the common fibular nerve, causing weak dorsiflexion and foot drop. (Kenhub: Fibula.)

Dislocation of the proximal tibiofibular joint is rare, under 1 percent of knee injuries, and is easily missed. It typically follows a fall onto a flexed, adducted knee, and the common fibular nerve can be injured with it. (TeachMeAnatomy: The Tibiofibular Joints.)

A segment of the fibula can be taken with its blood vessels as a free fibula flap. Surgeons use it to rebuild the jaw after large resections; it provides dense cortical bone, a long vascular pedicle and can bridge bony defects up to about 30 cm. (Fatani et al. Approach for Mandibular Reconstruction Using Vascularized Free Fibula Flap. Cureus 2022.)

The nearest named structures in the 3D model, measured from the centre of each part:

• Interosseous membrane of leg · skeletal
• Anterior tibial artery · cardiovascular
• Small saphenous vein · cardiovascular
• Fibularis longus · muscular
• Soleus · muscular
• Tibia · skeletal
• Plantaris · muscular
• Tibialis anterior · muscular
• Tibialis posterior · muscular
• Posterior tibial artery · cardiovascular