The latest developments in total hip arthroplasty materials: ceramic and polyethylene

Materials technology in total hip arthroplasty has made great advances in recent years. The great challenge for the total hip arthroplasty implant industry nevertheless remains the choice of material, not in the body of the implants, but in the bearing surfaces. The bearing surfaces are the two components on which the continual movement of the new artificial hip joint takes place after this operation. The industry's efforts in this area have been aimed at creating materials that can withstand millions of cycles of movement and minimise the friction between the two bearing surfaces. Traditionally, the bearing surface of the femoral implant consisted of a metal component, and that of the acetabular implant of a metal component and subsequently of polyethylene (plastic). In recent years these materials have been improved and modified. In the femoral implant the femoral head is now made of improved metal alloys, while in the acetabulum the metal implant has almost been abandoned and polyethylene has been almost entirely replaced by the highly cross link polyethylene type, that is, polyethylene with very high resistance to wear. The greatest advance of recent years, however, is the appearance of ceramic material for both the femoral head and the acetabulum. Ceramic appears to have far lower friction than the classic conventional materials.
There are many schools of thought that regard total arthroplasty with ceramic-on-ceramic bearing surfaces (that is, a ceramic femoral head and a ceramic acetabular cup) as the best option for minimising wear. In the literature, however, there is now a wide range of opinion and considerable disagreement as to the best choice of bearing surfaces. There are therefore views in favour of metal-on-polyethylene, ceramic-on-polyethylene and ceramic-on-ceramic bearing surfaces. All three options are generally considered to represent a modern choice of implant in total hip arthroplasty.
In a recently published article in the journal Hip International, a study was carried out comparing total hip arthroplasty systems using ceramic-on-ceramic and ceramic-on-polyethylene bearings. A systematic review and meta-analysis of the published randomised controlled trials was carried out in order to compare these implants.
The electronic databases were systematically searched, and the relationship between the bearing surfaces and the outcomes after total hip arthroplasty was investigated by two independent researchers. In all, 13 studies were reviewed, covering 2488 total hip arthroplasties. These papers were examined with regard to aseptic loosening, osteolysis, and rates of revision, femoral fracture, dislocation, deep infection, deep vein thrombosis and leg length discrepancy. The researchers found that there is no clear evidence on which to base the choice of ceramic-on-ceramic implants over ceramic-on-polyethylene implants. They also found that there is a need for further high-quality studies with longer-term evidence in order to clarify the choice of bearing surfaces in total hip arthroplasty.