Prosthetic knee joint. Colored frontal X-ray of a patient with a prosthetic knee (white, center). The artificial joint consists of two halves, one half attached to the femur (thigh bone) above the knee and the other half attached to the tibia (shin bone) below the knee. This is a hinge joint, which also allows a degree of rotation, imitating the mobility of the natural joint. Prosthetic knee joints are used to replace joints that have become stiff and painful as a result of arthritis or injury. Knee replacements can dramatically improve knee joint mobility, and can offer years of independence. The artificial components can, however, loosen with time.