The fibula is the name of one of the paired bones within the lower leg of humans. The other, the tibia, is much thicker, and the fibula connects to it by means of both appropriate articulation and ligaments.
Some tendons are contained within two major grooves at the distal, or bottom, end of the fibula (the lateral malleolus). These grooves redirect force on the joint, allowing less impact to be passed on to the tendons, and thereby minimizing damage.
The way that the two bones in the lower leg are positioned means that the fibula does not reach up as far as the knee joint; rather, its lower portion, including the specialized groove and tendon mechanism, forms part of the ankle joint, allowing for stability in movement. This is due to the fibula's major role as an anchor point for the various muscles and ligaments of the leg and ankle.
The fibula is not a structural bone and it is positioned on the outer edge of the lower leg. As a result, it is sometimes used as donor stock for bone grafts.