We report the findings from independent prospective clinical and laboratory-based joint-simulator studies of the performance of ceramic femoral heads of 22.225 mm diameter in cross-linked polyethylene (XLP) acetabular cups. We found remarkable qualitative and quantitative agreement between the clinical and simulator results for the wear characteristics with time, and confirmed that ceramic femoral heads penetrate the XLP cups at only about half the rate of otherwise comparable metal heads.

In the clinical study, 19 hips in 17 patients were followed for an average of 77 months. In the hip-joint simulator a similar prosthesis was tested for 7.3 million cycles.

Both clinical and simulator results showed relatively high rates of penetration over the first 18 months or 1.5 million cycles, followed by a very much lower wear thereafter. Once an initial bedding-in of 0.2 mm to 0.4 mm had taken place the subsequent rates of penetration were very small. The initial clinical wear during bedding-in averaged 0.29 mm/year; subsequent progression was an order of magnitude lower at about 0.022 mm/year, lower than the 0.07 mm/year in metal-to-UHMWP Charnley LFAs.

Our results show the excellent tribological features of alumina-ceramic-to-XLP implants, and also confirm the value of well-designed joint simulators for the evaluation of total joint replacements.

A pin-on-disc tribometer test with a rotating disc and a sector-wise loaded pin was used to determine friction coefficients for different material pairings. The four pin materials porcine cartilage, subchondral bone of the porcine cartilage, UHMWPE, vitamin E enhanced, crosslinked UHMWPE (VEPE) in combination with the three-disc materials zirconia toughened alumina ceramic (ZTA), CoCr, carbon-fibre-reinforced carbon (CrC) were tested. Stepwise loading was employed with the forces 10 N, 5 N, 2 N and 1 N. Test duration was 1 h. Diluted calf serum according ISO 14242-1 was used to determine the friction coefficients. The surface topography of all pins was examined using optical profilometry before and after the rotation tribometer tests. - No wear related modifications of the surface roughness parameters could be found. The coefficients of friction (COF) were lowest for the cartilage pins against all three-disc materials, with steady-state values between 0.01 and 0.02 for the highest applied load (10 N). Friction of subchondral bone yielded COF in the range 0.2 … 0.6, depending on the counterpart material. The two polyethylene materials behaved similar in this friction test with COF of about 0.1. The Ra roughness values of the different pins reflect the COF results: Ra of subchondral bone was one order of magnitude higher than Ra of the cartilage. This is in-line with the COF-values of bone being one order of magnitude higher than those of cartilage. These results will be discussed in view of the use of the disc materials as orthopaedic hemi-prostheses

We examined stainless-steel, cobalt-chrome, titanium and alumina and zirconia ceramic femoral heads retrieved at revision surgery. All the heads had articulated against ultra-high-molecular-weight-polyethylene (UHMWPE) acetabular cups. We studied the simulation of third-body damage and the wear of UHMWPE against the various materials used for the heads. The surfaces of the retrieved heads were analysed using a two-dimensional contacting profilometer. Third-body damage was characterised by the mean height of the scratches above the mean line (R. pm. ). The alumina ceramic and zirconia ceramic retrieved heads were found to have significantly less damage. In laboratory studies the ceramics were also more resistant to simulated third-body damage than the metal alloys. We studied the wear of UHMWPE against the damaged counterfaces in simple configuration tests. The damaged ceramics produced less polyethylene wear than the damaged metal counterfaces. The wear factor of UHMWPE against the damaged materials was dependent on the amount of damage to the counterface (R. p. ). Our study has shown the benefit of using the harder and more damage-resistant ceramic materials for femoral heads