Prosthetic hip. Coloured X-ray of a prosthetic (artificial) hip joint in place. Bones of the pelvis (red) and thigh-bones are seen; the prosthesis is at lower right. A prosthetic hip joint is used to replace a diseased hip joint typically as a result of arthritis, or fracture. During a hip replacement operation the ball at the end of the thigh bone is cut off and its rounded socket in the pelvis is enlarged. Metal joint components are then cemented in place of the damaged bone, the shaft (green/blue) fitting into a hollow inside the thigh bone. A hip replacement can dramatically improve hip joint mobility but the artificial components can loosen with time.