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Commentary & Perspective | ||||||||
Commentary & Perspective on In this issue of The Journal, Hamadouche et al. present the long-term results of an alumina-on-alumina articulation in total hip arthroplasty. The article is notable because the authors have reviewed a series of patients treated by Dr. Pierre Boutin, now deceased, who was one of the earliest advocates of alumina ceramics in total hip arthroplasty. Although a variety of problems related to design, materials, and fixation led to high failure rates of the early ceramic-on-ceramic designs used by Dr. Boutin and others1, Hamadouche et al. have wisely chosen to review a cohort of patients treated after some of these initial impediments had been overcome. This article is timely and important because it provides long-term results relevant to the current interest in strategies for reducing wear damage to bearing surfaces in joint replacements. Currently, three types of bearing surfaces have emerged as possible successors to the combination of metal-on-conventional polyethylene: cross-linked polyethylenes, metal-on-metal bearings, and ceramic-on-ceramic bearings2,3. Each has its own strengths and weaknesses4. Cross-linked polyethylenes have demonstrated excellent wear resistance in joint simulator studies and most are resistant to oxidative degradation. However, they have also demonstrated somewhat decreased mechanical properties on some tests, and there is little data supporting their clinical performance to date. Metal-on-metal implants have a limited but mostly favorable record in terms of clinical performance, but concerns remain about potential problems related to metal-ion release5. Ceramic-on-ceramic articulations, the subject of this article, potentially provide an even lower rate of wear than either metal-on-cross-linked polyethylene or metal-on-metal bearings6. The greatest concern about ceramic implants, however, is the risk of component fracture, which is always a catastrophic event with serious consequences. The present report provides very valuable information about the durability of one type of ceramic bearing, a 32-mm alumina-on-alumina articulation. The most important finding in this study was a radiographically undetectable rate of wear of the prosthetic components. This suggests that a ceramic-on-ceramic combination can provide a remarkably wear-resistant bearing surface over a long period of time, even in younger patients. Little osteolysis was seen, which demonstrates that the limited amount of ceramic debris generated by the bearing surface, whatever its particle size and quantity, did not lead to marked periprosthetic bone loss. Even in the few cases of limited periprosthetic osteolysis observed in this series, it is unclear whether the bone loss was caused by ceramic debris from the bearing surface or from metal, cement, or ceramic debris produced at secondary nonbearing interfaces. There were no ceramic fractures in this series. The prevalence of ceramic fractures has been reduced in recent years because of improvements in manufacturing techniques and in the matching of modular ceramic femoral heads with the metal trunions of femoral components. Nevertheless, the recent recall of some zirconia ceramic femoral head components, sold by many companies, highlights the fact that the risk of ceramic fracture still cannot be completely discounted. In this series, there were no dislocations, and the maximum abduction angle of the socket was 60°. Both of these facts are important and may contribute to the absence of some of the problems with use of ceramic-on-ceramic bearings that have been reported in other series. When dislocation occurs, it can lead to hard-on-hard bearing surface damage that may adversely affect long-term wear. Similarly, marked implant malposition can lead to edge-loading or prosthetic impingement, which, in the case of ceramic-on-ceramic bearings, can result in problems of catastrophic wear. One must be concerned that wider use of hard-on-hard bearings, particularly when the replacement is performed with suboptimal surgical technique, might increase the frequency of such problems, not seen in this series. Hamadouche et al. avoided many problems in study design that can undermine the conclusions of a retrospective, long-term follow-up study. Though not perfect, the rate of follow-up was high—90% at the last follow-up. And unlike some series done early in the experience with arthroplasty, the patient cohort is relevant to current practice: the underlying diagnosis in most was osteoarthritis or hip dysplasia; the mean age was sixty-two years; and twenty-five patients were younger than fifty years of age at the time of the arthroplasty. Some interesting information about ceramic bearings not included in this focused report may be found in the publications by Sedel et al., who have reported direct measurement of wear in retrieved alumina bearings7 and also have determined the histologic findings in periprosthetic tissue of ceramic-on-ceramic implants8. As in any retrospective, long-term follow-up series, there are limits to the conclusions that are relevant to present practice. Both cemented and uncemented acetabular and femoral components were used in this series, and it is notable that the rate of implant survivorship was satisfactory but not remarkable; in fact, the overall rate of implant survivorship free of failure at twenty years was lower than that of Charnley total hip arthroplasties performed with use of metal-on-conventional polyethylene bearing surfaces in most reports with a similar duration of follow-up. Of note, however, the failures in this series did not seem to be directly attributable to the ceramic-on-ceramic design, but rather were related to loosening of the ceramic socket from the cement, loosening of non-metal-backed uncemented ceramic implants from bone, or loosening of cemented titanium stems. These modes of failure are not likely to be common with use of the newer ceramic-on-ceramic prostheses that consist of modular metal-backed, porous-coated uncemented acetabular components combined with improved femoral component design. Much of the relevance of this report by Hamadouche et al. hinges on the possibility that newer generations of ceramic-on-ceramic implants9 can capitalize on the low wear rate of the bearing surface reported in this article while markedly reducing the problems, mostly related to implant fixation rather than the bearing surface, that led to clinical failures in this series. Caution here is important however—newer implant designs will introduce variables not present in this series. Modular, metal-backed acetabular implants probably will improve implant fixation; however, this modularity produces thinner ceramic on the acetabular side and introduces the potential for new problems related to locking of the ceramic and the metal, generating debris through the mechanism of micromotion between a ceramic insert and metal backing. In conclusion, this paper provides important information—unlikely to be available soon from other sources—concerning the long-term clinical performance of ceramic-on-ceramic bearings in total hip arthroplasty. A very low rate of bearing surface wear was identified and little osteolysis was seen. As surgeons consider the use of newer versions of ceramic-on-ceramic bearings and other alternative bearing surfaces for total hip arthroplasty, this kind of information is needed. *The author did not receive grants or outside funding in support of the research or preparation of this manuscript. He did not receive payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the author is affiliated or associated. References 1. Mahoney OM, Dimon JH 3rd. Unsatisfactory results with a ceramic total hip prosthesis. J Bone Joint Surg Am. 1990;72:663-71. | ||||||||
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