What are Hip Implants?
Hip implants are artificial devices that form the essential parts of the hip joint in a hip replacement surgery. The hip implants vary by size, shape, and material. Various components of a hip implant may be used for a hip replacement surgery. The components used may depend on the extent of damage to the hip joint, and the preference of your orthopedic surgeon.
What are Hip Implants composed of?
Implants are made of biocompatible materials that can be accepted by your body without producing any rejection response. Implants can be made of metal alloys, ceramics or plastics, and can be joined to the bone. The metals used include stainless steel, titanium, and cobalt chrome, and the plastic used is polyethylene.
Components of a Hip Implant
The components of a hip implant replicate the natural shape and structure of the ball-and-socket joint of the hip. The components used may depend on the size of your body and vary from patient to patient. A total hip replacement implant has three parts:
- Stem: The stem fits into the femur.
- Ball: The ball replaces the spherical head of the femur.
- Cup: The cup replaces the worn-out hip socket (acetabulum).
Types of Hip Implants
Based on your level of activity, any of the following types of hip implants may be used in a hip replacement surgery.
- Metal-on-polyethylene implant: The ball is replaced with a metal ball and the socket is replaced with polyethylene or has a polyethylene lining.
- Ceramic-on-polyethylene implant: The ball is replaced with a ceramic ball and the socket is replaced with polyethylene or has a polyethylene lining.
- Metal-on-metal implant: The ball and socket of the hip joint are replaced with a metal prosthesis. Metal-on-metal implants have greater durability compared to metal-on-polyethylene implants.
- Ceramic-on-ceramic implant: The ball is replaced with a ceramic ball, and the socket has a ceramic lining. They wear less than metal-on-metal implants and are most durable among the available hip implants.
- Ceramic-on-metal implant: The ball is replaced with a ceramic ball and the socket has a metal lining.
Types of Implant Fixation
Depending on your age and activity level, your surgeon may recommend any of the available three types of implant fixation.
- Cemented fixation: The femoral and acetabular components are held together with special bone cement. The bone cement is made from a special polymer called polymethylmethacrylate (PMMA). Most often, you can immediately be full weight-bearing and start walking. Cemented fixation is an option if you are less active. However, too much stress on the cemented fixation can lead to fatigue fractures.
- Cementless fixation: Cementless implants are coated with a porous material. They attach to the new bone that grows to the surface of the implant via bone ingrowth. The implant may be fixed using screws or pegs until bone ingrowth. You need to limit weight-bearing and use crutches or walker following cemented fixation to allow the bone to attach itself to the implant. Cementless fixation is an option if you are more active with good bone quality.
- Hybrid fixation: Hybrid fixation uses a combination of cemented and cementless fixation. The acetabular socket is inserted without cement and the femoral stem is inserted with cement.