Purpose: We compared two series of total hip arthroplasties (THA) at more than 12 years. The only difference between the two series was the nature of the femoral head: 28-mm zincronia head versus 32-mm alumina head.

Material and method: All THAs were performed during the same period (1988–1990) and the polyethylene inserts, the femoral components, the surgical cement and the operator were the same for both series. Patient age and mean weight were the same for the two series of 40 Zir/PE and 62 AL/PE implants: 98 and 63 years and 72 and 73 kg respectively. Implant survival, polyethylene wear on AP and lateral x-rays, and Merckel osteolysis were studied.

Results: Three revisions were required at eight, ten and eleven years in the Zir/PE group. No revisions were required in the Al/PE group where there were no signs of loosening on the radiograms.

During the first four years, polyethylene wear appeared to be the same in the two series. Beyond the fifth year, penetration of the alumina heads exhibited a regular mean 0.07 mm progression per year. Beyond the fifth year, penetration of the zircona heads accelerated reaching a mean 0.4 mm per year at twelve years. Mean volumetric wear of the polyethylene cups was 1360 mm3 for the zircona heads and 755 mm3 for the alumina heads. Osteolysis was seen as a defected facing the merckel and measured 2.5 cm2 for the Zir/PE couple and 0.35 cm2 for the Al/PE couple. The differences between the two series in linear penetration, volumetric wear, and osteolysis were significant (p < 0.05). The three zircona heads that were removed showed partial transformation from the tetragonal phase to the monoclinical phase (19%, 25% and 30%) and a roughened surface which was not sufficient to explain the polyethylene wear. Abnormal wear was explained more by loss of spherical shape and the greater volume of the zircona heads, probably related to a modification of the crystalline phase (change from the tetragonal to the monoclinical phase usually is associated with a 3% increase in volume). Analysis of the fingerprints left on the morse code of the zircona heads suggest the change in volume of the zircona heads was associated with a change in the contact between the morse cone and the zircona head over time. Analysis of the explanted cups showed wear with delamination in two cases. For one of the implants, the polyethylene insert was deformed exhibiting a fusion aspect corresponding to abnormal increase in temperature.

Discussion and conclusion: The zircona implants manufactured more than twelve years ago probably do not meet current manufacturing standards. Nevertheless, the changes observed in the explanted pieces would suggest they are related not only to the manufacturing process but also to the material itself.

Although alumina has been used in orthopaedic surgery since the 1970s, the long-term clinical results of zirconia have not been well documented in vivo. We studied hips with these two different ceramics during the same period and with a minimum follow-up of ten years. Because the size of the alumina and zirconia heads was different, hips with 32 mm alumina heads and those with 28 mm zirconia heads were compared with control hips with stainless-steel heads of the same size. Our aim was to compare the two ceramics.

There was an increased linear rate of penetration of the femoral heads into the liner between years five and 12 for the zirconia and the stainless-steel groups. This was severe in the zirconia group (0.4 mm/year compared with 0.13 mm/year for the stainless-steel group). During the same 12-year period there was, however, no significant change in the rate of wear in the alumina group (0.07 mm/year). The mean wear at the most recent follow-up was 1360 mm³ for the 28 mm zirconia group, 683 mm³ for the 28 mm stainless-steel group, 755 mm³ for the 32 mm alumina group and 1314 mm³ for the 32 mm stainless-steel group. The monoclinic content rose on the surface of three zirconia heads which were retrieved at revision. This change was associated with an increase in the surface roughness. A change in the roundness with an increase in the sphericity deviation was also observed both in the articular and non-articular parts of the femoral heads. The increase in rate of wear in the zirconia group was only evident after eight years and may be linked to a long-term biodegradation of zirconia in vivo, associated with the altered roughness and roundness which was observed on the retrieved heads.