The kneecap, also called the patella, is found in front of the knee joint, which is the junction between the femur, the upper leg bone, and the tibia, the lower leg bone. Flanking the kneecap are the medial epicondyle of the femur and the lateral epicondyle of the femur. Just beneath them are the lateral condyle and the medial condyle of the femur.
The kneecap itself is surrounded by a large tendon that's made up of four tendons from the high muscles. These muscles allow a person to straighten her leg and her thigh. Ligaments also help to keep the knee stable. Because it's actually enclosed in a tendon and not attached to one, the kneecap is considered a sesamoid bone.
There's a pointed bone at the top of the tibia that's called the intercondylar eminence. Beneath it and to the sides are the lateral condyle and the medial condyle of the tibia. Right beneath the lateral condyle of the tibia is the head of the fibula. Another tendon from the lower tip of the kneecap attaches to the tibia.
The knee joint is unusual in that it's the largest joint in the body but is covered only by skin and ligaments. Only the patella protects it.