MODEL RELEASED. Hip replacement surgery. Surgeon during a hip replacement operation. This is carried out when hip joints become stiff and painful due to arthritis or a severe break. The ball at the top of the femur (thigh bone) is removed and replaced with a metal ball. This is held in place by a shaft which is glued into a cavity drilled in the femur. The socket in the pelvis is also removed and replaced with a plastic cup which holds the ball. Hip replacements can provide years of mobility for patients, but often become loosened and need to be replaced.