The fibula or calf bone is a leg bone located on the lateral side of the tibia, with which it is connected above and below. It is the smaller of the two bones, and, in proportion to its length, the slenderest of all the long bones. Its upper extremity is small, placed toward the back of the head of the tibia, below the level of the knee joint, and excluded from the formation of this joint. Its lower extremity inclines a little forward, so as to be on a plane anterior to that of the upper end; it projects below the tibia, and forms the lateral part of the ankle joint. The bone has the following components: -Body of fibula that presents four borders—the antero-lateral, the antero-medial, the postero-lateral, and the postero-medial; and four surfaces—anterior, posterior, medial, and lateral. -Lateral malleolus or The Lower Extremity that is of a pyramidal form, and somewhat flattened from side to side; it descends to a lower level than the medial malleolus. -Interosseous membrane connecting the fibula to the tibia, forming a syndesmoses joint -The superior tibiofibular articulation is an arthrodial joint between the lateral condyle of the tibia and the head of the fibula. -The inferior tibiofibular articulation (tibiofibular syndesmosis) is formed by the rough, convex surface of the medial side of the lower end of the fibula, and a rough concave surface on the lateral side of the tibia. Blood Supply The blood supply is important for planning free tissue transfer because the fibula is commonly used to reconstruct the mandible. The shaft is supplied in its middle third by a large nutrient vessel from the fibular artery. It is also perfused from its periosteum which receives many small branches from the fibular artery. The proximal head and the epiphysis are supplied by a branch of the anterior tibial artery. In harvesting the bone the middle third is always taken and the ends preserved (4 cm proximally and 6 cm distally) The fibula is ossified from three centers, one for the shaft, and one for either end. Ossification begins in the body about the eighth week of fetal life, and extends toward the extremities. At birth the ends are cartilaginous. Ossification commences in the lower end in the second year, and in the upper about the fourth year. The lower epiphysis, the first to ossify, unites with the body about the twentieth year; the upper epiphysis joins about the twenty-fifth year. Fibula Flap The fibula flap has been used extensively for oromandibular reconstruction. A long segment of bone up to approximately 22 cm is available for harvest. The skin paddle has proven to be dependable if care is taken to preserve the fasciocutaneous perforators. The blood supply to the fibula is derived primarily from the peroneal artery, which branches from the popliteal or posterior tibial at the trifurcation point of the posterior tibial, anterior tibial, and peroneal just distal to the popliteal fossa. The primary blood supply to the harvested fibula flap is derived from periosteal perforators traveling circumferentially around the fibula. The fibula head lies 3 cm below the lateral femoral condyle. Distally the fibula is subcutaneous and forms the lateral malleolus. The fibula itself bears approximately 10% of the weight placed on the foot. The common peroneal nerve crosses the proximal fibula between 4 to 8 cm below the head and can be palpated as it crosses the bone. As the common peroneal nerve crosses the bone it lies under the extensor digitorum longus and peroneus longus muscles. The common peroneal nerve branches to form the superficial and deep peroneal nerves, both of which supply extensor muscles of the foot. Injury to these nerves may result in foot drop. The lateral septal band separating the anterior from posterior compartments carries 2 to 6 septocutaneous perforators that run between the peroneus musculature and the soleus. These septocutaneous perforators are primarily located in the region of the middle third of the fibula. These septocutaneous perforators occasionally run posterior to the true septum through the flexor hallucis longus and lateral soleus muscles and in this situation they are more appropriately termed musculocutaneous perforators. True septocutaneous perforators and some musculocutaneous perforators may be present in the same specimen. The skin supplied by these vessels lies on the lateral and posterior lower leg. The lower 7 to 8 cm of the fibula and its surrounding fibrous attachments are important for ankle mortise ligament support and should not be disrupted. Both the anterior tibial neurovascular bundle (anterior to the interosseous septum) and the posterior tibial neurovascular bundle (deep to the soleus and medial to the flexor hallucis longus muscle) are encountered during the dissection, and a thorough knowledge of the anatomy and care with the dissection are important to prevent injury to these structures. Branches of the lateral sural cutaneous nerve supply the area of the skin paddle and can be harvested to allow innervation of the flap. The sural nerve lies within the field and can be harvested as a vascularized nerve transfer with the flap. This robust nerve is used in cases where a cable nerve graft is required.