Three bones meet in the knee: the thighbone (femur), the shinbone (tibia), and the kneecap (patella). In any joint, including the knee, a cycle of breakdown and repair of tissue continuously carries on; old tissue is replaced by new, keeping the knee healthy and alive. However, when tissue breakdown exceeds repair, a stress reaction begins. In the knee, this most often occurs where the patellar tendon (a ligament that attaches the shinbone to the kneecap) attaches to the front bump of the tibia, or shinbone. This area is known as the "tibial tubercle." In older children and teens, when the stress on the tendon exceeds the strength of the cartilage, the two may begin to separate, causing pain and swelling.