Partial knee replacement. Artwork of the bones and ligaments (right and left) surrounding an implant (centre left) that has replaced part of the knee joint. Here, the medial (inner) articulation between the femur (thigh bone, top) and the tibia (shin bone, bottom) has been replaced with an implant. As only one part of the joint has been replaced, this is known as unicompartmental knee arthroplasty. Partial knee replacements are used when only part of the knee is affected by conditions such as osteoarthritis. Here, the patella (knee cap) is largely unaffected, and the cruciate ligaments (centre) are still intact.