The current hip joint replacement prosthesis is composed of four major components:
- A metal socket that replaces the acetabulum. The acetabulum is the concave surface of the pelvis. The head of the femur meets with the pelvis at the acetabulum, forming the hip joint.
- A liner with highly polished inner part representing the articular surface. An articular surface is the surface of a joint at which the ends of the bones meet. The liner is usually plastic, but other materials are also used such as ceramic or metal. The liner allows the hip to move smoothly.
- A metal stem that is inserted in the femoral canal; and
- A metal or ceramic ball, which articulate with the liner.
There are two types of implants:
- Cemented hip replacement system, which was first described by Sir Charnley and is still currently used with some modifications and
- A biological non-cemented system, which depends on the body ingrowth or ongrowth on the metal surface.