Outcome studies have indicated that primary total hip replacement is among the most cost-effective interventions of any surgical procedure. The article by Röder et al. highlights this point and demonstrates that postoperative functional outcome, including walking capacity and hip flexion, are closely tied to preoperative function. Irrespective of preoperative function, however, pain relief was universal and, as others have found, was immediate and long lasting after primary total hip replacement.
While there are many indications for primary total hip replacement, the principle ones are related to pain and loss of function. How best to evaluate pain and loss of function over time is the question the authors are attempting to answer. Their review of the literature would suggest that other outcome measures, including the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and the Short Form-36 (SF-36), are variable in terms of their accuracy in reporting an association between low postoperative scores and preoperative scores. This, however, has not been our experience. I suspect, given the methodology available in 1967, that other scores, such as the WOMAC and the SF-36, could not be collected at the time of the initiation of the International Documentation and Evaluation System European hip registry (IDES).
The importance of the information obtained from this paper, and hence the conclusion, depends on the accuracy of data at the time of collection. This study by Röder et al. addresses the timing of intervention and demonstrates that, if surgery is put off until function has been severely compromised, patients are generally less likely to be as satisfied with functional recovery after total hip replacement.
If the notion is accepted that it is important to collect information on outcome after primary total hip replacement, then, to reduce the revision burden, the question must be asked—How best can we inform the orthopaedic community at large of this information?
The current study, in effect, is a retrospective review of a prospectively collected case series. Critical to the success of the IDES Registry, or any registry, for that matter, is the quality control of the collected information. The IDES Registry collects information by means of a paper-based system and punch cards, with the data being entered by a data-entry person in a central location. This method was implemented in 1967 because of its simplicity. Whether or not this method is able to identify and accurately correct errors is unknown. Data in any registry need to be validated, a step that is even more important in a study such as this one, which had sixty-five participating hospitals and clinics in eight different countries. Thus, there needs to be an ability to match the data from each hospital, not only with the patient (which the authors have done) but also with data collected by the hospital or the clinic, as the case may be. One of the problems with retrospective case series with prospectively collected data is that the centers contributing the data are most likely specialized in joint replacement surgery, and thus their results may not be generalizable to the orthopaedic community at large. This is particularly important in the United States, where 52% of primary total hip replacements and 77% of revision total hip replacements performed in Medicare patients are being carried out by surgeons who do ten or fewer of these procedures annually1. Thus, it is unrealistic to expect that the results from low-volume surgeons would be likely to mirror the results presented from this registry.
It is important for any registry to be able to disseminate information to the orthopaedic community not only regarding successes, but also regarding failures (revision rates). Perhaps the most important function of a registry is that it allows surgeons to identify implants that seem to have a higher short-term failure rate than others. One of the weaknesses of this paper is that there is no information regarding the type of hip prosthesis used. There are over 100 different hip implants available for use, with some requiring cement fixation and others requiring either cementless fixation or a combination of both (hybrid). The choice of prosthesis has not been explained in this study, and no attempt has been made to identify surgeon error or prosthetic-specific reasons for failure. In my view, this is the most important value of a case-based series and, unfortunately, the authors have been unable to offer any information in that regard. On the other hand, the information which they do offer, namely, that poor preoperative mobility and function are predictors of poorer postoperative recovery of function, is indeed important. In the early days of total hip replacement, orthopaedic surgeons were more interested in pain relief as the only important outcome when recommending total hip replacement to patients with primary osteoarthritis. Today, as "baby-boomers" are reaching the age at which hip replacement is offered and as hip replacement is beginning to be offered at a younger and younger age, it will be even more important to have information available to allow our policy makers and clinicians, as well as the public and patients, to make evidence-based decisions. While there is no doubt that the economic consequences of unrelieved pain and suffering associated with osteoarthritis of the hip have been well documented, it is nevertheless equally important to ensure a reproducible and sustained functional outcome after total hip replacement. The data in this paper give us considerable reassurance of sustained functional outcome.
While it is tempting to be critical of case-based series, this study demonstrates that very valuable information can ensue from this methodology.
The alternatives to case-based studies such as this, of course, include meta-analysis. In this type of study, a specific question to be answered is identified and appropriate inclusion criteria are determined, and then the results of several studies on that subject are reviewed. As a result, meta-analysis is able to enlarge the sample size, and hence the validity, of the conclusions. While meta-analysis works well in certain areas of surgery, it has nonetheless been criticized because of its lack of a randomization process as part of the inclusion criteria. This fact makes its usefulness somewhat limited in total joint replacement2.
It is tempting to suggest that randomized clinical trials should be the gold standard for the assessment of new technology in total hip replacement. From a practical standpoint, however, it is difficult to generalize the results from one particular implant to another by a randomized clinical trial process because of the large number of different implants on the market and because of ongoing redesigns of implants. Also, as a result of constantly changing technology, randomized clinical trials are extremely expensive and are thus of limited value in assessing outcome after total hip replacement1.
The IDES Registry has withstood the test of time. It has demonstrated that it is possible to develop a voluntary registry within different clinics and universities in several different countries. This has been done by achieving effective cooperation of clinicians and hospitals as well as hospital staff and, most importantly, patients. The IDES registry has proven to be a powerful tool for use in analyzing and disseminating information such as that regarding fixation method and implant type. In addition, it allows comparison of the joint replacement practices of surgeons in different countries around the world. Despite its shortcomings, it can be used to identify the potential revision burden associated with different implants and should facilitate comparisons with other registries. In addition to the use of IDES, a number of countries, including Sweden, Finland, Norway, and Denmark as well as Canada, Australia, and England, have established a National Joint Replacement Registry, which, in my view, is the wave of the future3-7.
When registry data are incomplete, as seems to be the case with IDES, the data are much more prone to selection bias. The authors address that issue in their manuscript and unfortunately, there is very little they can do to correct that problem. The information contained in the IDES database could better inform the orthopaedic public if it were stratified (e.g., according to the type of implant, method of fixation, age at the time of primary surgery, and body mass index). However, it is important that outcome measures are carefully documented preoperatively, and this study goes a long way toward making that point.
*The author did not receive any outside funding or grants in support of his research for or preparation of this work. Neither he nor a member of his immediate family received 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, division, center, clinical practice, or other charitable or nonprofit organization with which the author, or a member of his immediate family, is affiliated or associated.
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2. Laupacis A, Bourne R, Rorabeck C, Feeny D, Tugwell P, Wong C. Comparison of total hip arthroplasty performed with and without cement: a randomized trial. J Bone Joint Surg Am. 2002;84:1823-8.
3. Graves SE, Davidson D, Ingerson L, Ryan P, Griffith EC, McDermott BF, McElroy HJ, Pratt NL. The Australian Orthopaedic Association National Joint Replacement Registry. Med J Aust. 2004:180:S31-4.
4. Malchau H, Herberts P, Eisler T. Garellick G, Soderman P. The Swedish Total Hip Replacement Register. J Bone Joint Surg Am. 2002;84:S2-20.
5. Utting MR, Lankester BJ, Smith LK, Spencer RF. Total hip replacement and NICE. BMJ. 2005;330:318-9.
6. Canadian Joint Replacement Registry (CJRR) 2006 report: total hip and total knee replacements in Canada. Toronto: Canadian Institute for Health Information; 2006. p 47-52.
7. Maloney WJ. National joint replacement registries: has the time come? J Bone Joint Surg Am. 2001;83:1582-5.