The patella is the small, flat bone at the front of your knee. Most people call it the kneecap. If you sit down and feel the front of your knee, that hard, movable disc under your skin is your patella.

Your patella serves as a shield, protecting the knee joint from bumps and impacts. It also works like a pulley, helping the powerful muscles in your thigh straighten your leg more efficiently. When you kick a ball, jump rope, or climb stairs, your patella glides up and down in a groove at the end of your thighbone, making those movements possible.

The patella is actually a special type of bone called a sesamoid bone, meaning it's embedded within a tendon. It's the largest sesamoid bone in your body. Because it sits right at the surface and takes a lot of stress during running, jumping, and kneeling, the patella can be prone to injury. Athletes sometimes experience patellar tendinitis (inflammation of the tendon attached to the kneecap) or dislocate their patella if they twist their knee awkwardly.