Masaru Ueno

Advances in zirconia toughened alumina biomaterials for total joint replacement

The objective of this article is to provide an up-to-date overview of zirconia-toughened alumina (ZTA) components used in total hip arthroplasties. The structure, mechanical properties, and available data regarding the clinical performance of ZTA are summarized. The advancements that have been made in understanding the in vivo performance of ZTA are investigated. This article concludes with a discussion of gaps in the literature related to ceramic biomaterials and avenues for future research.

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.

Comparison of the Wear Properties of Polyethylene Plate in Total Knee Prostheses (TKP) using Different Femoral Component Materials

INTRODUCTION Polyethylene wear debris generated from articulating surface can cause the osteolysis and late aseptic loosening of components even in total knee replacements (TKR). To minimize the wear of polyethylene tibial plates, the alumina ceramics was introduced as the femoral component material in Japan in 1982. In 2001, zirconia ceramics as the advanced ceramic material with high fracture toughness was introduced as the femoral components material. Although these ceramic materials are accepted with good clinical results [1], it remains to be elucidated how ceramic femoral components act effectively to reduce the clinical risks caused by the polyethylene wear debris. In this study, to evaluate the wear properties of polyethylene tibial plates articulated with three different femoral component materials (alumina ceramics, zirconia ceramics and Co-Cr alloy), the knee simulator tests were performed.

Needs of Bioceramics to Longevity of Total Joint Arthroplasty

Wear on alumina / UHMWPE-THP decreased by 25-30% of that on met al / UHMWPE in hip simulator test and clinical results. Wear on THP of alum ina / alumina was near zero in hip simulator test. In knee simulator test, UHMWPE wear against lumina decreased to 1/10 of that against metal. Clinically we have no revision case due to PE we ar problems for 23 years. In retrieved cases, UHMWPE surface against alumina was very s mooth. On UHMWPE surface against metal, many fibrils and scratches were found. In IBBC loosening in acetabulum occurred in 2.5% in 268 joints in only early cases at 16 to 14 years after THA. Only one joint was revised. At revision THA with massive bone defect, HA granules were filled. Socket migrations in two joints and partial spaces in two joints occurred in total 40 joints at 17 to 5 years. Bioceramics was found to be indispensable in enduring total joint arthroplasty . Introduction In order to keep the longevity of total joint arthroplasty, extrem ely low wear bearing materials and maintaining adequate fixability to the bone forever are desired. In our experimental and long term clinical experiences, it has been found that bioceramics, including bioinnert and bioactive ceramics, have been playing a maj or p rt in enduring total joint arthroplasty. The production of particulate wear debris from implant materials a nd subsequent osteolysis has been recognized as the major cause of long term failure in tot al hip replacement. The basic strategy to address the problem of osteolysis should be to reduce the number of polyethylene particles generated by improving the materials at the articulating count erfaces. The use of a ceramic femoral head has been advocated especially in young active patients because it produces less polyethylene wear compared with a conventional metal femoral head. However, an attempt to eliminate the use of polyethylene has been made through the use of metal-on-metal and ceramic-on-ceramic articulations. In 1970, to increase the wear resistance of polyethylene, wear te sts w re performed on RCH 1000 [ultrahigh molecular weight polyethylene (UHMWPE), molecular we ight, 106] irradiated at several levels of high-dose gamma radiation emitted by 60Co. The wear ra te was smallest at 100 Mrad. Sockets cross-linked by gamma radiation at 100 Mrad were used clinically from 1971 to 1978. We also experimentally confirmed that UHMWPE (molecular weig ht, 6 x 106) showed less wear in an alumina-on-UHMWPE combination than in the metal-on-UHMWPE combina tion. In 1977, we began to use 28 mm alumina balls. In our clinical experience, it was found that the thicker the poly ethylene socket, the lower the wear rate. To use a thicker UHMWPE sockets, the femoral head size was decreased with time: 26 mm alumina femoral heads were used from 1989 to 1994, 22 mm alumina femoral h eads were used from 1994 to 1995, and 22 mm zirconia femoral heads were used from 1995 to 1996. S ince 1996, Key Engineering Materials Online: 2003-05-15 ISSN: 1662-9795, Vols. 240-242, pp 735-754 doi:10.4028/www.scientific.net/KEM.240-242.735

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 gammairradiation 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 × 106 cycles. In contrast, non-packaged 100 Mrad PE showed considerable wear: 47.0 mg at run-in ((0–0.25) × 106 cycles) and 114.1 mg at the end of 5 × 106 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.

Radiographic and retrieval wear analyses of the first generation highly cross-linked polyethylene cup against a ceramic femoral head

In this study, the in vivo wear of highly cross-linked polyethylene (CLPE) cups against alumina ceramic femoral heads was evaluated by radiographic and retrieval analysis. The radiographic wear of six ethylene oxide gas-sterilized (i.e., non-cross-linked) conventional polyethylene (PE) cups with the mean follow-up of 20.9 years and 60 CLPE cups with the mean follow-up of 7.4 years was measured. The retrieved 16 PE cups with clinical use for mean 21.5 years and 10 CLPE cups with clinical use for mean 2.9 years was evaluated as a retrieval analysis. In the radiographic analysis, the linear wear of CLPE cups was significantly lower (99% reduction) compared to conventional polyethylene cups. The results of retrieval analyses for both cups were similar to those of radiographic analyses. Even when third-body wear occurred during clinical use, no surface damage was observed on the surface of ceramic femoral heads. The surface is not sensitive to third-body wear, and hence, the ceramic femoral head has a great advantage in terms of the wear of CLPE under third-body wear conditions. In conclusion, CLPE cups used with alumina ceramic femoral heads in total hip arthroplasty should have favorable wear resistance in several in vivo situations.

Carboxymethyl-chitin promotes chondrogenesis by inducing the production of growth factors from immune cells.

Many techniques have been tested for their ability to restore cartilage defects, but several problems still remain in the complete healing of injured cartilage. In our previous study, we found that a carboxymethyl-chitin/beta-tricalcium phosphate (CM-chitin/beta-TCP) composite induced cartilage regeneration in the osteochondral defects of rabbits in vivo. We also found that CM-chitin stimulated peritoneal exudate cells (PEC) in mice and induced several kinds of inflammatory cytokines and transforming growth factor beta-1 (TGF-beta1). In this study, we examined whether CM-chitin is responsible for the induction of chondrogenesis via the production of TGF-beta1 in vitro. The murine pluripotent cell line C3H10T1/2 was maintained as a micromass culture in conditioned medium prepared from PEC stimulated with and without CM-chitin. CM-chitin-conditioned medium induced RNA expression of the chondrogenic-factor Sox9 and the matrix proteins aggrecan, Col2a1, and Comp. Their expression levels were decreased in the presence of anti-TGF-beta1 antibody. The micromass tissues cultured in CM-chitin conditioned medium at day 21 were clearly stained by Toluidine blue or Alcian blue (histological staining) and collagen II antibody (immunohistological staining), showing the expression of acidic glycosaminoglycan and type II collagen. Similar results were observed in micromass tissue stimulated with TGF-beta1 as a positive control. However, no chondrogenesis occurred when CM-chitin was added directly to a C3H10T1/2 cell culture. These results indicated that CM-chitin is a potent inducer of chondrogenesis via the induction of TGF-beta1 in immune cells.

Influence of Complex Frictional Heating and Mechanical Stress Effect for Surface Crystalline Structure Change of Zirconia Femoral Head

Several clinical reports pointed out that the monoclinic transformation of crystalline structure of zirconia femoral head with clinical service time can cause the changes of surface roughness and mechanical properties. To elucidate the relationship between these surface roughness change induced by phase transformation and UHMWPE socket wear, hip simulator wear tests were performed on total hip prostheses (THP) up to 6 million cycles running. Four groups of different surface monoclinic phase fraction of Kyocera zirconia heads were prepared by aging treatment prior to the wear tests. The surface roughness/ wear rate of zirconia heads with 0, 10, 50 and 80mol% monoclinic phase fraction were 0.009/ 3.8, 0.014/ 3.9, 0.012/ 3.7 and 0.010µmRa/ 3.1mg/million cycles, respectively. These results exhibit that the surface roughness change induced by phase transformation does not significantly influence extent of the generation of UHMWPE debris in Kyocera zirconia /UHMWPE THP system. In contrast, the surface roughness exhibited complex relation with the monoclinic phase fraction and therefore the morphological analysis was performed on the zirconia articulating surfaces

Wear, Friction, and Mechanical Investigation and Development of Alumina-to-Alumina Combination Total Hip Joint

Since 1962, when Charnley proposed and used ultrahigh-molecular-weight polyethylene as the material of choice for the low-friction hip joint, many clinical successes have been achieved. However, there are also many cases in which the excessive wear of particles of polyethylene can result in late aseptic loosening. To solve the critical issues resulting from polyethylene wear, a new all-alumina hip joint was developed by considering the design from the viewpoints of friction, wear, and mechanical strength. The all-alumina hip joint, with 28 mm head diameter, 5–35 itm radial clearance, <0.02 μm Ra surface roughness, <± 1 μm sphericity, and semispherical with polyethylene armored inlay design, has good friction and wear properties, as well as strength. By using the inlay with polyethylene liner for assembly in the metal shell and dispersing the load to the alumina inlay and metal shell, a reduction in stress is expected. Providing as much shock-absorbing capability as possible to an all-alumina hip joint appears to be required for safety.

Investigation of the Wear Properties of Ceramic Total Hip Prostheses Made of Alumina and Zirconia Combination: A Hip Simulator Study

Introduction Since late 1980’s, zirconia ceramic has been used as the materi al for femoral heads of total hip prostheses (THP) because of its high fracture toughness and good wear performance such as relatively low generation of wear debris when used with polyethy l ne acetabular cup [1]. Currently, the use of zirconia femoral head is predominant in Japan for THP applications. However zirconia on zirconia bearing for THP itself is still controvertial in t erms of wear performance, and only limited number of attempts in laboratory wear tests for alumina-zirconia bearing have been made [2]. The aim of this study is to investigate the wear properties of zi rcon a components by hip simulator tests, when used in combination with zirconia and alumina as a counter surface.