Fibula

The fibula is the slender outer bone of the leg, beside the tibia, reaching from below the knee to the outer ankle.

At a glance

English: Fibula
Latin (TA2): Fibula
System: Bone
Region: Lower limb
Side: Paired, left and right
Muscles on it: Extensor digitorum longus

About the fibula

The fibula is the thin outer bone of the leg, running beside the tibia on its outer side. For its length it is the slenderest of the long bones. Its upper end tucks in beneath the back of the tibia's lateral condyle, taking no part in the knee joint, while its lower end reaches beyond the tibia to form the outer side of the ankle.

The head at the top is roughly square, with a flat facet facing up and inwards to meet the tibia at the superior tibiofibular joint, a small synovial plane joint. A pointed apex projects upwards from the back of the head. The tendon of biceps femoris and the knee's lateral collateral ligament both attach to the head, the ligament splitting the tendon in two. The common fibular nerve winds round the narrow neck just below, where it can be felt and is easily compressed.

The shaft is twisted and ridged, with borders and surfaces that mark the edges of the leg compartments. Its front gives origin to fibularis tertius and the long extensors of the toes and great toe; its lateral face to fibularis longus and brevis; its back to soleus and flexor hallucis longus; and its medial side to tibialis posterior. The interosseous border holds the membrane that links it to the tibia. At the lower end the lateral malleolus forms the outer bump of the ankle, with an articular facet against the talus. Above it the two leg bones are held together by a strong fibrous joint, the distal tibiofibular syndesmosis.

The fibula carries little of the body's weight. Its main jobs are to steady the ankle and to provide surfaces for muscle. Most fibular fractures are at the ankle; the Weber system grades them by whether they lie below, at or above the syndesmosis. A Maisonneuve injury is a spiral break high in the fibula with tearing of the syndesmosis and damage on the inner ankle. Because the middle of the shaft can be removed with its fibular artery supply while the ends are left intact, it is a standard graft for rebuilding the jaw.

Function and supply

Function: Stabilises the ankle through the lateral malleolus and anchors the muscles of the lateral, anterior and posterior leg.
Nerve supply: The common fibular nerve curves round the neck of the fibula and divides there into its superficial and deep branches.
Blood supply: The middle of the shaft is fed by the fibular artery, through a nutrient vessel and through its periosteum, while the head and upper end are fed from the anterior tibial artery.

Parts of the fibula

Each number is marked on the model. Press one, here or on the model, to see it named in place.

Anterior border of fibulaMargo anterior fibulaeThe front edge of the shaft, starting in front of the head and running straight down before dividing near the ankle. Its two lower limbs enclose a triangular area just above the lateral malleolus, and the anterior intermuscular septum attaches along it.
Anteromedial surface of fibulaFacies anteromedialis fibulaeThe narrow strip of shaft between the anterior border and the interosseous crest, facing forwards and inwards. The long toe extensors and fibularis tertius take origin here: extensor digitorum longus higher up, extensor hallucis longus in the middle.
Apex of head of fibulaApex capitis fibulaeThe pointed tip rising from the back of the fibular head. The knee's lateral collateral ligament and part of the biceps femoris tendon attach close by.
Articular facet of head of fibulaFacies articularis capitis fibulaeA flat, round joint surface on the top and inner side of the head. It meets a matching facet under the tibia's lateral condyle at the superior tibiofibular joint.
Articular facet of lateral malleolusFacies articularis malleoli lateralisThe smooth triangular surface on the inner side of the lateral malleolus. It meets the outer side of the talus and forms the outer wall of the ankle joint socket.
Body of fibulaCorpus fibulaeThe long, thin, twisted shaft, with ridges that serve as edges for the muscle compartments of the leg. It carries little of the body's weight but anchors many muscles of the leg and foot.
Head of fibulaCaput fibulaeThe knob-like upper end, roughly square in outline, lying just below and behind the outer knee. Biceps femoris and the lateral collateral ligament attach to it, and it can be felt beneath the skin.
Interosseous crest of fibulaCrista interossea fibulaeA sharp ridge on the inner side of the shaft that faces the tibia. The interosseous membrane joining the two leg bones attaches along it.
Lateral malleolusMalleolus lateralisThe rounded lower end of the fibula that forms the bony bump on the outer side of the ankle. It reaches lower than the medial malleolus and is the most commonly broken part of the ankle.
Lateral surface of fibulaFacies lateralis fibulaeThe outer face of the shaft, between the anterior and posterior borders. Fibularis longus and brevis arise from it, and it turns backwards near the ankle to lead into the malleolar groove.
Malleolar fossaFossa malleoli lateralisA rough pit set behind and below the malleolar joint facet. The posterior talofibular ligament attaches into it.
Malleolar groove of fibulaSulcus malleolaris fibulaeA shallow channel on the back of the lateral malleolus. The tendons of fibularis longus and brevis run in it on their way to the foot, held in place by a retinaculum.
Medial border of fibulaMargo medialis fibulaeA ridge on the back of the shaft, also called the medial crest, running from the inner side of the head down to join the interosseous crest in the lower part of the bone. It splits the posterior face into the areas for tibialis posterior and for the flexors.
Medial surface of fibulaFacies medialis fibulaeThe face of the shaft between the interosseous crest and the medial border. It is grooved and gives origin to tibialis posterior.
Neck of fibulaCollum fibulaeThe narrowed segment just below the head. The common fibular nerve winds round its outer side, where a tight cast, a fracture or pressure can injure it and cause foot drop.
Posterior border of fibulaMargo posterior fibulaeThe prominent back edge of the shaft, beginning at the apex of the head and ending at the back of the lateral malleolus. The posterior intermuscular septum attaches along it.
Posterior surface of fibulaFacies posterior fibulaeThe back of the shaft, between the posterior and medial borders. Soleus arises from its upper part and flexor hallucis longus from most of the rest.
Posteromedial surface of fibulaFacies posteromedialis fibulaeThe area on the back of the shaft that faces backwards and inwards, behind the medial crest. Flexor hallucis longus arises from it, and lower down it becomes continuous with the triangle above the malleolar facet.

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At a glance

About the fibula

Function and supply

Related structures

See the fibula where it really sits, with every layer of the body around it.