The tibia is the bigger of the two bones in the lower leg. The other is the fibula (calf bone). The tibia runs from just under the knee to the ankle. It’s the second longest bone in the human body and an important part of the human ability to stand and move. The tibia also supports several muscles, tendons, nerves, and ligaments. Because it is so strong, it usually takes severe trauma, like a fall or car accident, to break the tibia.

Source: Cleveland Clinic