The patella is commonly referred to as the kneecap. It is a small, freestanding, bone that rests between the femur (thighbone) and tibia (shinbone). The femur has a dedicated groove along which the kneecap slides. As a form of protection, both bones also contain cartilage — strong, flexible tissue — in the areas near the patella.

The kneecap plays a vital role in how the knee bends, in addition to most motions that require movement of the leg. If the patella or the tendon associated with it becomes injured, a person will experience difficulty walking, running, standing, or engaging in athletic activity. If dislocated, the kneecap can no longer slide along the thighbone's grooves, which can aggravate and damage cartilage on both the femur and the tibia.

Dislocation and other traumatic injuries are common among athletes and other people who are extremely physically active. Injuries tend to be more pronounced in high impact sports. For example, patella-related injuries are common in sports like football, mixed martial arts, and wrestling.