The tibia is the shin bone, one of the two crural bones of the leg. (Tibia = a flute, because it can be used as such with the ends cut off and holes drilled into it).
It is much stronger and more massive than the other crural bone, the fibula. Its shaft is approximately triangular in cross section and its anterior border and medial surface can be readily felt just below the skin at the front of the leg; this is why a kick on the shins is especially painful since there is little depth of soft tissue to absorb the injury.
The tibia has expanded upper and lower ends. The upper end forms the tibial plateau consisting of two condyles (with a ridge or intercondylar eminence between them) which articulate with the two condyles of the femur to form the knee joint. The lower end possesses a medial protrusion - the medial malleolus - which can be readily felt at the ankle.
The tibia possesses a anterior tuberosity just below the condyles into which the quadriceps tendon is inserted. Moreover, the shaft of the tibia is the insertion for thigh muscles such as sartorius, gracilis , semimembranosus and semitendinosus, as well as the origin of muscles acting on the foot such as tibialis anterior, tibialis posterior, flexor digitorum longus and soleus and the popliteus muscle which plays a role in knee action.
The tibia not only takes part in the knee and ankle joints, it also has a series of articulations with the fibula 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.