Fibula is lateral bone of the leg. It is weaker and smaller than tibia (the medial bone of leg). It is not directly involved in transmission of weight of body. It consists of a proximal end, a long shaft and a distal end forming lateral malleolus. The overall shape of fibula varies in form, being variably molded by attached muscles.
Proximal end of fibula:
Proximal end of fibula consists of head and neck.
- Head: The head of fibula articulates with the fibular facet present in the lateral condyle of tibia.
- Neck: Neck of fibula connects the head with the shaft. It is important clinically because of its relation with the common peroneal nerve, which crosses posterolaterally and can be rolled against it.
Shaft of fibula:
The shaft is highly variable in form. Commonly it consists of three borders and surfaces, each associated with a particular group of muscles.
- Anterior Border: Anterior border descends from anterior aspect of fibular head to apex of lateral malleolus.
- Posterior Border: Posterior border is continuous with the medial margin of lateral malleolus.
- Medial Border: The medial (interosseous) border gives attachment to the interosseous membrane.
- Lateral surface: It lies between anterior and posterior borders. It is associated with peroneal muscles.
- Anteromedial surface: It lies between anterior and interosseous borders. It is associated with extensor muscles.
- Posterior surface: It lies between interosseous and posterior borders. and is associated with flexor muscles.
Distal end of fibula:
Distal end of fibula forms the lateral malleolus
It projects distally and posteriorly, with lateral aspect being subcutaneous. It is the distal articular surface of fibula and takes part in the formation of ankle joint. Correspondingly, it provides attachment to many ligaments of this joint.
Blood supply of fibula:
The nutrient foramen lies a little proximal to the midpoint of posterior surface. The nutrient artery which passes through this foramen is a branch of peroneal artery. The proximal end recieves metaphyseal arteries from genicular anastomosis. Similarly the distal end recieves metaphyseal arteries from anastomosis around ankle joint.
Nerve supply to fibula:
Proximal end is innervated by nerves supplying the knee joint and superior tibiofibular joint. Similarly the distal end is innervated by nerves supplying the ankle joint and inferior tibiofibular joint. Periosteum of fibula is innervated by nerves supplying the muscles attached to it.
Ossification of fibula:
Fibula ossifies from three centers, one for shaft and one for each end. The process of ossification starts at about eighth week of intrauterine life in the shaft. In the distal end it begins in the first year while in the proximal end it begins in third year. Distal epiphysis unites with the shaft at about fifteenth year while proximal epiphyses does not unite until about 17 years despite having appeared earlier. Thus fibula does not follow the usual pattern of ossification of long bones according to which the secondary center appearing first is last to unite. But in fibula the secondary center appearing first is first to unit.