The prosthetic acetabulum is a component of a prosthetic hip and is similar in design to the femur with a head, a neck and a femoral component. The acetabulum, a cup-shaped depression at the base of the hipbone (into which the ball-shaped head of the femur fits, forming a ball and socket joint), is drilled out and replaced with an artificial socket. The prosthesis is made of a metal alloy, usually titanium. Both prosthetic parts are held in place by a porous surface material allowing growth of bone into the prosthesis, or sometimes, by a special glue. It is not uncommon for an artificial hip to last up to fifteen years or longer. An artificial or prosthetic hip is often used for fractures or severe arthritis.