Hip replacement loosening occurs over time, and can cause problems with the normal function of the hip replacement prosthesis. When a hip replacement is placed into the body, it is either press-fit into the bone, or cemented into position. Either way, it is fit tightly into the bone of the thigh (femur) and pelvis so that the implant cannot move. When implants loosen, the hip replacement can begin to move small amounts. Usually, this is associated with increasing pain and loss of motion experienced by the patient.