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Dog · Skeletal system

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Model: 3D Dog Bone Project, Massey University (School of Veterinary Science and Institute of Natural and Mathematical Sciences), nzfauna on Sketchfab, CC BY-SA 4.0

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Fibula

Long, slender, lateral bone of the leg. It bears little weight, but gives origin to muscles and forms the lateral malleolus that stabilises the tarsus.

Laterality:: Paired (left and right)

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Overview

The fibula is a long, gracile bone lying lateral to the tibia and of similar length. In the dog it keeps its full length, unlike in ungulates, where it is reduced. Its main function is not to bear weight, which is the job of the tibia, but to provide an origin for several muscles and to act as the lateral stabiliser of the tarsal joint.

Head

The head (caput fibulae) is the flattened proximal end, which articulates with a small facet on the caudolateral face of the lateral tibial condyle (proximal tibiofibular joint, with very little movement). The lateral collateral ligament of the stifle attaches to it. The common fibular (peroneal) nerve crosses just caudal to the head, in a very superficial position.

Shaft

The shaft (corpus fibulae) is thin and slightly flattened; it is separated from the tibia by the interosseous space of the leg (spatium interosseum cruris), occupied by the interosseous membrane and wider in the proximal half. Its lateral surface gives origin to the fibular muscles (longus and brevis) and the lateral digital extensor; its caudal surface to part of the digital flexors.

Lateral malleolus

The distal end thickens to form the lateral malleolus (malleolus lateralis), which articulates with the tibia (distal tibiofibular joint) and laterally with the talus and the calcaneus. It carries a groove for the tendons of the fibular muscles and the lateral digital extensor, and gives origin to the lateral collateral ligament of the tarsus, with its long and short parts. It is palpable as the lateral prominence of the hock.

Clinical relevance

Fractures: the fibula rarely breaks on its own; it usually fractures together with the tibia. In those cases it needs no fixation of its own, unless it is used to add rotational stability to the repair.
Fractures of the lateral malleolus: equivalent to an injury of the lateral collateral ligament of the tarsus and cause instability; they are reduced and fixed with pins and a tension band.
Shearing injuries: in road traffic accidents, friction against the asphalt can strip off the lateral malleolus and the collateral ligament.
TPLO: the osteotomy of the proximal tibia is made next to the fibula, and fibular fracture is a recognised complication of the technique.
Fibular nerve: its superficial course beside the head makes it vulnerable to trauma and to compression by bandages.