Types of Hip Implants
Each hip implant system is made up of four components:
In a total hip replacement, the following components are implanted to recreate the ball and socket joint of the hip: femoral stem, head and cup (which consists of a cup and liner). The stem fits into the femur and connects with the head. The head replaces the femoral head and sits inside the cup, which replaces the worn acetabulum.
In total hip replacement surgery, the damaged parts of the hip are replaced with artificial components referred to as implants or prostheses. These components will mimic the anatomy and movements of the anatomy it replaces.
Ceramic components may be used as a treatment option for Total Hip Replacement. The liner and/or ball components can be made out of alumina ceramic which can move against each other or the ball against a polyethylene liner. Ceramic can produce the lowest quantity of wear particles in laboratory testing compared to all known combinations of bearing materials for total hip replacements. Modern medical grade ceramic is very hard and scratch resistant.
Advantages to ceramic total hips include:
- High wear resistance
- Relatively no toxicity of wear particles
- Long clinical experience
Risks to ceramic total hips include:
- Sensitive to proper positioning of components
- Chipping of the ceramic cup liner
- Risk of fracture in old models
Metal-on-metal Total Hip Implants consist of both the ball and cup components made of metal. Direct metal-on-metal coupling does not have a soft cushion to dampen repeated stresses that occur from the contact of the leg with the floor during walking.
Advantages to metal-on-metal hip system:
- Favors larger diameters of ball and cup components
- High resistance to wear
- Fewer failures due to producing less wear particles
- Low friction in laboratory studies
Risks to metal-on-metal hip system:
- Increased metal ions in blood circulation
- Large components – the larger the surface, the more it wears
Cemented fixation relies on a stable interface between the prosthesis and the cement and a solid mechanical bond between the cement and the bone. Cemented fixation is recommended for older patients, patients with rheumatoid arthritis, and for younger patients with compromised health or poor bone quality and density.
Cementless fixation attaches directly to bone and new bone grows into the implant surface. This type of fixation requires a longer healing time because it relies on new bone growth for stability. Cementless fixation is most often recommended for younger, more active patients, and patients with good bone quality.
Hybrid Fixation of Prosthesis
Hybrid fixation is when one component, usually the acetabular socket, is inserted without cement and the other component, usually the femoral stem, is inserted with cement.