The Journal of Bone and Joint Surgery
(American) 83:1582-1585 (2001)
© 2001 The Journal of Bone and Joint Surgery, Inc.
The Orthopaedic Forum
William J. Maloney, MD
Department of Orthopaedic Surgery, Washington University School of Medicine, 660 South Euclid Avenue, Campus Box 8233, St. Louis, MO 63110. E-mail address: email@example.com
The author did not receive grants or outside funding in support of his 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.
Total joint replacement surgery is widely recognized as one of the most cost-effective interventions in medicine today. The impact that these procedures have on quality of life has been well documented1. New implants are designed and manufactured with the expectation that they will be equivalent or superior to existing products. Regardless of how much testing is done prior to product release, in reality our patients are the final testing grounds for new devices. Only in our patients do all of the variables that affect outcomethat is, design issues, material issues, manufacturing issues, patient-related factors, and surgical techniquefinally come into play. As a result, premature failures can and do occur.
We then have to ask ourselves two questions. First, is the magnitude of the problem of premature failure serious enough to warrant the expenditure of resources? Second, if so, what is the optimal way to disseminate information in order to have a timely and positive effect on the problem?
To answer the first question, we have only to look at the revision burden in the United States. Review of Medicare data shows that in 1996 and 1997 revisions accounted for approximately 17% to 18% of all total hip replacement procedures2. Despite improvements in surgical technique and in the designs of prostheses, revision rates do not seem to be declining over time. In 1993 the revision burden was approximately 16.8%, and it increased to approximately 17.3% in 19972. There are numerous examples of implants and technologies that did not perform as expected for a variety of reasons. Examples include carbon-fiber-reinforced polyethylene, Hylamer, heat-pressed polyethylene, and metal-backed patellae, to name just a few. It is also important to remember that the data on revisions reflect procedures performed in Medicare beneficiaries, who in general are older than sixty-five. It is likely that the revision burden in our younger patients is even higher; however, there is currently no accurate way to document this.
If one accepts that our revision burden is too high and that this burden is related at least in part to products that do not perform as intended, we then have to answer the second question: how do we disseminate information in the orthopaedic community? There are three potential basic methodologies for studying implant performance. These include randomized clinical trials, meta-analyses, and retrospective case series. Prospective, randomized clinical trials remain the gold standard for evaluation of medical interventions. However, when it comes to joint replacement procedures, these trials simply are not practical. A recent issue of Orthopedics Today lists more than twelve manufacturers of hip implants, with more than fifty femoral components alone. Performance of a randomized clinical trial to examine the relative effectiveness of currently available systems in the United States would be not only cost-prohibitive but also of limited value. As an example, Rorabeck et al. performed a randomized clinical trial of hip replacements3. They compared the results of arthroplasties performed with and without cement and demonstrated the beneficial aspects of hip replacement. However, their data currently are of limited value as they relate to the performance of a specific implant and, since that study, the manufacturer has made changes to virtually every aspect of the system. The two types of metal-backed acetabular components that were used have both been redesigned, the sterilization method for the polyethylene has changed, and the ion-implanted titanium femoral heads that were used were replaced with cobalt-chromium heads. Only the tapered cementless titanium-alloy femoral component has remained unchanged.
Meta-analysis is another technique with which to analyze a given technology or intervention. With meta-analysis, the literature is critically reviewed and studies that meet specific inclusion criteria are included with the hope that the sample size, and thus the validity of the conclusions, can be increased. One common inclusion criterion for meta-analysis is randomization. Since randomized clinical trials evaluating the relative efficacy of hip and knee replacement designs have not been, and will not be, carried out in large numbers, meta-analysis is not going to be of major help in this arena.
What we are then left with are retrospective case series. There is no doubt that these are of value, bringing to light both positive and negative factors that influence outcome. When it comes to implant performance, however, it is important to realize that there are limitations to retrospective case series, which most often represent the experience of a single surgeon or center. These surgeons and centers are often recognized subspecialized experts in the field of joint replacement surgery, and thus their experiences do not necessarily reflect what occurs in the general orthopaedic community, where the majority of procedures are done by surgeons who perform less than fifteen hip replacements per year. In addition, the surgery may be done by the innovator, which introduces potential bias. Finally, and perhaps most importantly for the orthopaedic community and our patients, is the fact that retrospective case series are not reported in a timely enough fashion to serve as an early warning system for technologies with problems.
Hylamer polyethylene is a good example of a material with problems. Hylamer was a form of polyethylene in which the crystallinity of the material and the size of the crystalline regions were increased. The objective was to increase the strength and fatigue resistance of the polymer by creating larger crystallites and to increase the proportion of the polymer that was in the stronger crystalline phase. Laboratory testing of the altered polyethylene demonstrated an 8% lower mean wear rate and fatigue-crack-growth tests indicated a reduction in the crack-growth rate, which were hypothesized to increase its fatigue life4. Despite the in vitro results, however, clinical performance was not as expected. In retrospect, accelerated polyethylene wear was noted as early as one to three years after surgery. The material was released in late 1990, potential problems were first reported in the literature in 19965, and marketing was discontinued in 1997. Press-fit sockets with a hydroxyapatite coating applied to a relatively smooth surface is another example of a situation in which information concerning potential problems could have been disseminated in a more timely manner. Hydroxyapatite-coated femoral components have had an excellent track record; however, hydroxyapatite on a macrotextured acetabular component did not fare as well. In a retrospective series6, the failure rate was 22% at five to nine years after surgery. The implant was released to the market in 1991; the report on the magnitude of the problem did not come out until 1998, long after the product was removed from the market.
Recognizing that a lack of timely dissemination of information is currently a problem, we have to ask how it can be done better. One answer is a national joint replacement registry, the goal of which is threefold. First, a national joint replacement registry must accurately define the epidemiology of joint replacement surgery in a particular patient population. This goal seems trivial, but in fact it is not. To understand the importance of reported failures, we need to know the number of prostheses that are being implanted. We currently have only estimates about what implant technologies are being used in which patients and about the true revision rate. As documented in Sweden, a national registry can provide accurate data regarding which prostheses are being implanted and which prostheses are being removed7.
The second goal of a national registry is to provide timely information for the orthopaedic community on the outcomes of joint replacement. The end point obviously has to be clear and unequivocal. In a national registry, the end point for failure is revision surgery. An implant that is being revised has by definition failed; that is not controversial. A national registry may be less accurate in documenting the cause of failure, but it provides information as to where potential problems might be and directs future analysis toward problem areas. Since information is gathered in real time and can be analyzed on an ongoing basis, it has the potential to bring to our attention problems that may be occurring long before they would be reported to the orthopaedic community by traditional methods. This would obviously benefit all of the stakeholders in this arena, including surgeons, manufacturers, payers, and most importantly patients. From this standpoint, a national registry can serve as an effective postmarket surveillance tool, a responsibility that technically lies with the United States Food and Drug Administration. However, surveillance by the Food and Drug Administration rarely extends beyond three years, which in the world of joint replacement is inadequate.
The third general goal of a national joint replacement registry is to identify risk factors for a poor outcome and, through continuous feedback to participating centers and surgeons, to improve outcomes. Again, to determine if this is a realistic goal, we can turn to the Swedish Hip Registry, which was established in 1979. The stated goals of the Swedish Hip Registry were to describe the outcomes of primary hip replacement and to provide information regarding serious complications. The hypothesis of its founders was that, by sharing information on outcomes, individual hospitals would be able to compare their results with national averages. Units with poor outcomes would improve by following the best example. This is now referred to as evidence-based medicine. The success of this registry in improving the quality of hip replacement in Sweden has been well documented8,9. The registry identified specific technical factors that are associated with improved outcomes of femoral replacement with cement, including porosity reduction and plugging of the femoral canal. Once identified, this information was provided to the orthopaedic community, leading to a change in practice. The prevalence of use of a distal femoral plug increased from approximately 30% in 1982 to >95% in 1987. Over the past two decades, the percentage of revision hip replacements has been cut in half, and currently it is approximately 8% in Sweden compared with 18% in the United States.
One of the concerns of the orthopaedic community in the United States is that a national registry will drive patients to major centers. This in fact has not been the case in Sweden. The percentage of primary hip replacements done in rural hospitals in Sweden increased from <20% in 1981 to approximately 40% in 1999. At the same time, outcomes improved substantially at the more poorly performing centers.
Other attempts have been made in the United States to ensure the safety of medical devices entering the market. The Safe Medical Devices Act of 1990 was enacted by Congress on November 28, 1990. The intent of this law was to ensure that medical devices are safe and effective by monitoring so that the Food and Drug Administration learns about serious problems and quickly removes defective devices. Technically, this act requires that facilities in which medical devices are to be used report to the Food and Drug Administration problems that "contribute to the death, serious illness or serious injury of the patient." Under this act, orthopaedic surgeons are required to identify device problems and then supply information identifying the device and the nature of the problem.
In June 1993, the Food and Drug Administration introduced MedWatch. This program had three basic components: (1) medical device reporting (MDR) by manufacturers, (2) an effort that encourages reporting by doctors and other health-care professionals, and (3) a user-facility reporting requirement as mandated by the Safe Medical Devices Act. This regulation defines an injury as any event requiring medical or surgical intervention to preclude impairment of a body structure or function. This definition includes all revisions of hip and knee replacements, but obviously complete reporting is not occurring as only a small percentage of revision arthroplasties are actually being reported. It should be noted that the Food and Drug Administration does not have adequate staff to investigate the few reports that they currently receive, and certainly it would not be able to handle properly reports on the thousands of hip and knee revisions that occur each year.
Despite its failure to achieve the stated goals, MedWatch includes a critical component relating to confidentiality. Under the Freedom of Information Act any MedWatch report is subject to public disclosure, but only after the report has been purged of confidential details, including the names of patients and health-care professionals. The concept of confidentiality is critical for the success of any joint replacement registry. Participants must be assured that the registry will not be used in a punitive way. In a litigious society such as ours, legislation may be required to further protect the integrity of a national joint replacement registry to ensure that the data are used as intendedto serve as an early warning system for premature device failure and to improve outcomes for our patients.
Currently, there are joint replacement registries in Sweden, Finland, Norway, Denmark, Hungary, and Canada, and registries are being evaluated in New Zealand, Australia, and England. In England, the development of a national registry was mandated by the government in response to a recent problem with a hip replacement system that had an exceedingly high failure rate and was subsequently recalled. The registries in these countries are financed by the government, as one would likely be in the United States.
The establishment of a national joint replacement registry with federal support requires consideration of both practical and political realities. Practical challenges include an examination of costs, construction and management of the data, governance of the database, and access to the data. Political challenges involve review of applicable federal laws as they relate to confidentiality and privacy rules as well as to discoverability.
While the goals and objectives of a national joint replacement registry seem consistent with the mission of several federal agencies that are concerned about providing good-quality patient care, cost is an obvious issue. Although a national registry would be expected to have a high initial operating cost, the potential cost-savings in the long run could be substantial. Barrack et al.10 estimated that the cost of a routine revision total hip replacement was approximately $18,000. For a complex revision, the cost goes up to as high as $30,000. If it is estimated that 10% of revisions are complex, the average cost of all revisions in the United States would be approximately $19,200. As 200,000 hip arthroplasties are performed annually in the United States and the revision burden is 18%, 36,000 revisions are performed annually. If the number of revision hip replacements could be decreased by 5% (1800), an estimated cost-savings of more than thirty million dollars could be realized.
The evidence that a national joint replacement registry would benefit our patients is strong. These registries have the capacity to define the epidemiology of joint replacement, to serve as an early warning system for premature device failure, and to identify factors that are associated with both good and poor outcomes. On the basis of evidence, practices can be driven toward following the best example through feedback to hospitals and surgeons. The time has come to initiate such an effort in the United States.