The knee is a hinge joint formed by two bones (femur and tibia) and is held together by four ligaments (medial collateral ligament, lateral collateral ligament, anterior cruciate ligament, posterior cruciate ligament).
The patella, or knee cap, also is part of the normal knee anatomy. The ends of the femur and tibia and underside of the patella are covered by articular cartilage, a slippery surface which allows friction-free, painfree movement.
