The fibula (= clasp or brooch, because sheep fibulae were used to pin cloaks before the advent of buttons) is the smaller of the two "crural bones" i.e. the bones of the leg; the larger bone is the tibia. It possesses a long thin shaft (which normally bears little weight) and has expanded extremities.
The upper extremity - the head - can be readily felt through the skin about
an inch below the knee; it articulates with the tibia at a small synovial joint.
The tendon of biceps femoris and the fibular collateral ligament of the knee
are both inserted into the head of the fibula.
Just below the head is the constricted neck of the fibula around which the common peroneal nerve passes forwards to gain access to muscles and skin in the front of the leg. The nerve is extremely vulnerable at this site and injury may lead to "foot drop".
The lower extremity of the fibula is the lateral malleolus, the bony projection which is readily felt at the ankle. The shaft of the fibula, although relatively thin, is also extremely complex with a number of borders and surfaces. It provides attachment for one of the invertors of the foot (tibialis posterior), evertors of the foot (peroneus longus + brevis), dorsiflexors (such as extensor digitorum longus, extensor hallucis longus), and plantar flexors (such as soleus and flexor hallucis longus). It articulates with the tibia by means of the proximal tibiofibular joint (a small synovial joint), the distal tibiofibular joint (a strong fibrous joint or syndesmosis) and the interosseous membrane which runs between the interosseous borders of the tibia and fibula.
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