Ceramic versus cobalt-chrome femoral components; wear of polyethylene insert in total knee prosthesis.

The present study aimed to determine the effect of femoral component materials and sterilization methods on wear properties of total knee prostheses by using a knee simulator test and retrieval analysis. The simulator test revealed that ultrahigh molecular weight polyethylene (UHMWPE) inserts had remarkably lower wear against the ceramic femoral component than against the Co-Cr femoral component. However, the retrieval study revealed no significant difference in the linear wear between the former and the latter. The alumina ceramic/UHMWPE insert combination showed a mild wear. However, whether cross-linking by gamma-ray sterilization reduces wear remained unconfirmed. In contrast, oxidative degradation and/or delamination was confirmed. Thus, we conclude that alumina ceramic/ethylene oxide gas-sterilized UHMWPE insert in a total knee prosthesis might exhibit a good wear resistance.

Oxidation and wear of 100-Mrad cross-linked polyethylene shelf-aged for 30 years.

Some previous studies suggest that aging influences wear and oxidatively degraded nonsterilized ultra-high-molecular-weight polyethylene (UHMWPE) exhibits decreased wear resistance. We therefore asked whether shelf-aging storage conditions influenced degradation and wear resistance of gamma-irradiated UHMWPE. We examined oxidation and wear of 100-Mrad gamma-irradiated UHMWPE (100-Mrad polyethylene) cups shelf-aged for 30 years without (n=2) or with (n=2) packages. The oxidation index of the unpackaged 100-Mrad polyethylene surface (4) was higher than that of the packaged one (2.7). The packaged 100-Mrad polyethylene cup exhibited a high wear resistance with a steady wear rate of 0.5 mg/10(6) cycles. In contrast, the unpackaged 100-Mrad polyethylene exhibited an extremely high initial wear rate of 187.9 mg/10(6) cycles over the first 0.25 x 10(6) cycles with a subsequently reduced wear rate of 5 mg/10(6) cycles after 5 x 10(6) cycles. Packaging over long periods inhibits surface oxidation and maintains the wear resistance of gamma-irradiated UHMWPE cups.

THA with hydroxyapatite granules at cement-bone interface: 15- to 20-year results.

UNLABELLED: To augment cement-bone bonding, we interposed hydroxyapatite granules at the cement-bone interface (bioactive bone cement technique). Hydroxyapatite granules (2-3 g) were smeared on the bone surface of the acetabulum and femur just before cementing. We used porous hydroxyapatite granules 300 to 500 microm in diameter from 1986 to 1988 (first generation) and granules 100 to 300 microm in diameter from 1989 to 1991 (second generation). We followed 151 patients (222 hips) in the first generation and 170 patients (252 hips) in the second generation. The minimum followup was 15 years (mean, 17.3 years; range, 15-20 years). Radiolucent lines or spaces less than 1 mm were observed in four hips (1.8%) in the first generation and in 15 hips (6.2%) in the second generation. Osteolysis was observed in one hip (0.5%) in the first generation and six hips (1.6%) in the second generation. We observed loosening in two cups (0.8%) in the second generation. The long-term clinical results suggest the interface bioactive bone cement technique combined with our other techniques results in low incidences of radiolucent lines (spaces) and osteolysis, and may increase the longevity of cemented THA. The data suggest the larger hydroxyapatite granules performed better than smaller ones. LEVEL OF EVIDENCE: Level III, therapeutic retrospective cohort series. See the Guidelines for Authors for a complete description of levels of evidence.

Histologic findings at 14 and 18 years after cemented total hip arthroplasty with interface bioactive bone cement technique.

To augment cement-bone bonding in total hip arthroplasty, we interposed hydroxyapatite (HA) granules at the interface. We report the histologic findings of 2 cases 14 and 18 years after cemented total hip arthroplasty with this technique. We found that a thick bony layer was observed where rich layers of HA granules existed. In areas without HA granules, the trabeculae did not form a thick bony layer. These bony layers around HA granules were observed at the interface of non-weight-bearing and weight-bearing areas in 2 acetabula after long-term follow-up.

Wear of '100 Mrad' cross-linked polyethylene: effects of packaging after 30 years real-time shelf-aging.

Studies have shown that gamma-irradiation of polyethylene (PE) generally results in degradation by surface oxidation. However, from 1970 to 1978 Oonishi et al. used ultra-high-molecular-weight polyethylene (UHMWPE) cross-linked and sterilized by 100 Mrad of gamma-irradiation in air (100 Mrad PE) for total hip prostheses, and obtained excellent clinical results extending for 30 years. In the present study, we used a hip joint simulator to investigate the wear characteristics of 100 Mrad PE cups which had been shelf-aged for an extremely long period (30 years). The PE cups, aged in an air-containing triple polyethylene package for 30 years (packaged 100 Mrad PE), showed low wear with 3.4 mg of weight loss, even after 5 x 10(6) cycles. In contrast, non-packaged 100 Mrad PE showed considerable wear: 47.0 mg at run-in ((0-0.25) x 10(6) cycles) and 114.1 mg at the end of 5 x 10(6) cycles. The substantially, lower wear even in the presence of an oxidized surface layer for the packaged 100 Mrad PE, was comparable to the low wear seen on retrieved 100 Mrad PE after 30 years of clinical use. The long-term shelf-storage conditions, which affect the surface oxidative degradation of PE, are assumed to be the key factor in the wear-resistance of gamma-irradiated UHMWPE.

Wear of highly cross-linked polyethylene acetabular cup in Japan.

The wear characteristics of ultra-high-molecular-weight polyethylene acetabular cups irradiated with 6.0 to 7.5 Gy of gamma-irradiation were studied in a hip simulator and in vivo in 70 hips for 6 to 39 months. The linear wear was 2.5% to 4.5% of the wear seen in conventional polyethylene cups. A biphasic wear pattern was observed over time with a relatively large wear in the first year and a subsequent leveling of the wear rate curve. The linear wear rate in the second phase (steady state) was 0.006 mm/y. The extent of decrease in clinical wear of 6.0-Mrad polyethylene (Aeonian, Kyocera Corp, Kyoto, Japan) cups is comparable with the decrease of the in vitro wear measured by the hip simulation test.

Change in UHMWPE properties of retrieved ceramic total knee prosthesis in clinical use for 23 years.

The alumina-ceramic total knee prosthesis developed by Kyocera Corp. was implanted in 1979, and was in clinical use for 23 years until total knee arthroplasty revision surgery in January 2002. It is believed that this is the longest clinical period of a ceramic total knee prosthesis reported to date in the world. In the present study, we gave consideration to the long-term clinical stability of the alumina-ceramic femoral component as well as the mechanism of in vivo degradation of ultrahigh molecular weight polyethylene (UHMWPE) based on the evaluated wear, oxidation, and fracture toughness of the retrieved UHMWPE. We concluded that the degradation of UHMWPE by progressive oxidation is an issue to be solved in the future. To moderate stress concentration, use of a thin UHMWPE insert should be avoided. The low wear rate and the mild wear pattern observed this time suggest the possibility of reduced wear of the UHMWPE against the alumina-ceramic femoral component, and the usefulness of the alumina-ceramic total knee prosthesis component was recognized even after long clinical use.