Anatomy Guide › Lower limb
Patella
The patella, or kneecap, is a bone that grows inside a tendon. Bones of this type are called sesamoid bones, and the patella is by far the largest in the body. It sits embedded in the quadriceps tendon at the front of the knee, gliding up and down a groove on the femur every time the knee bends — you can feel it slide if you cup your knee and slowly straighten your leg.
Its job is mechanical advantage. By holding the quadriceps tendon away from the knee's axis of rotation, the patella acts like a pulley spacer, increasing the muscles' leverage by as much as a third to a half. Climbing stairs, rising from a chair, and jumping all lean on this boost. The underside of the patella bears the thickest cartilage anywhere in the body — up to about half a centimeter — because the compressive forces during a deep squat can reach several times body weight.
The patella's position makes it both essential and exposed. A fall directly onto the knee or a dashboard impact can crack it, and because the quadriceps pulls on it slightly outward, the kneecap can dislocate sideways, especially in adolescents. The familiar knee-tap reflex test works through the patella: the tap stretches the patellar tendon just below it, triggering the quadriceps to twitch.
In Anamo, the patella is the front-and-center landmark of the knee cluster, neighboring the femur above, tibia below, and the cruciate ligaments deep behind it. When knee-region heat lights up, the kneecap is the reference point everything else is measured from.
- The largest sesamoid bone — a bone that forms inside a tendon
- Boosts quadriceps leverage by up to half
- Carries the thickest cartilage in the human body on its underside
- The knee-tap reflex is tested through its tendon
Think you could find the patella on a 3D model? Play Anamo and test yourself — every guess is color-coded by how close it lands to the mystery structure.