Over the past twenty years, orthopaedic surgeons in the United States have made a gradual but definitive progression in total hip arthroplasty—from cement fixation to hybrid fixation and then to cementless fixation. These changes in the choice of fixation occurred despite the lack of clear scientific evidence to support the widespread adoption of cementless total hip arthroplasty in broad groups of patients. In fact, during that time, accumulated data from the Swedish Total Hip Register continued to support the use of cemented components in a wide spectrum of patient groups1. In this issue of The Journal, Mäkelä et al. provide population-based evidence from the Finnish Arthroplasty Register that cementless total hip replacements have proved more durable than cemented total hip replacements when the total hip procedure is performed in patients who have a diagnosis of primary osteoarthritis and are fifty-five to seventy-four years of age. Furthermore, cementless total hip replacements proved as durable as cemented total hip replacements when performed for primary osteoarthritis in patients who were seventy-five years of age or older. That information, combined with prior data on the advantages of cementless total hip arthroplasty for young, active patients (younger than fifty-five years), begins to provide the scientific support for wider adoption of cementless total hip arthroplasty in broad groups of patients2.
The authors of this study have rightly pointed out the limitations inherent in any registry-based study. Those limitations include potential bias if not all patients in the population of interest are captured in the registry and the need to use the hard end point of revision as the definition of failure (failing to capture impending radiographic failures or patients who refused revision surgery despite clinical failure). Of interest in this particular study, however, is the appreciation of the power of large retrospective reviews to add to our collective understanding of important clinical questions. In this age of so-called evidence-based medicine, a hierarchy of research design is often suggested, with randomized controlled trials at the top of the pyramid and with observational studies generally viewed as having less validity. Recently, however, it has become clear that while large multicenter randomized clinical trials do have substantial power to answer important clinical questions, so too do large well-designed retrospective reviews3,4. That is particularly true of observational studies that include a case-control design or a contemporary cohort design. Mäkelä et al. have done an excellent job in defining clear cohort groups in the present study, and that strengthens the findings of this large retrospective review.
The recent reporting in the news media of the suspension of sales of one acetabular component has reignited calls for a nationwide implant registry5. While it is clear that a registry is of value in helping to identify poorly performing implant designs, it is less clear if the overall effect of a registry would be to promote or impede progress in the development of better implant designs. It is intellectually interesting to consider the differences in how implant choices have been made in Sweden, Finland, and the United States over the past several decades, and such an exercise quickly highlights the difficulties in determining an ideal model for progress. In Sweden, the systematic reporting of results from the Arthroplasty Registry was accompanied by educational efforts specifically aimed at improving cementing techniques for total hip arthroplasty. Those efforts helped maximize the results obtained with cemented total hip replacements, but an unintended consequence may have been the subsequent underutilization of cementless total hip replacements, with the net result being unclear. In Finland, the Arthroplasty Register recorded eighty-four different femoral-stem designs that were used in fewer than fifty operations, suggesting that systematic review resulted in the early withdrawal of a substantial number of underperforming designs. The danger in the early reporting of failures occurs when the data are extrapolated to condemn a concept as opposed to being used to highlight problems with a specific design. One could easily imagine a scenario in which the early Finnish data could have been interpreted to argue against the entire concept of cementless total hip replacements. In the United States, we have depended largely on the reporting of results of smaller, retrospective clinical reviews to establish the track record of various implants. We have utilized the marketplace and the actions of individual surgeons to shape our implant choices. Interestingly, the accumulated data suggest that, at the present time, this market-based approach has largely been successful in moving us toward good implant choices. What price was paid along the way (e.g., because of underperforming implants left on the market too long) remains unclear and difficult to quantify. As we collectively consider implementation of a national joint registry in the United States, however, let us keep in mind the weaknesses as well as the strengths of the data that can be gleaned from such an effort.
*The authors did not receive any outside funding or grants in support of their research for or preparation of this work. One or more of the authors or a member of his or her immediate family received, in any one year, payments or other benefits in excess of $10,000 or a commitment or agreement to provide such benefits from a commercial entity (DePuy, Zimmer). Also, a commercial entity (Stryker, Zimmer, DePuy) paid or directed in any one year, or agreed to pay or direct, benefits in excess of $10,000 to a research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which one or more of the authors, or a member of his or her immediate family, is affiliated or associated.
1. Herberts P, Malchau H. Long-term registration has improved the quality of hip replacement: a review of the Swedish THR Register comparing 160,000 cases. Acta Orthop Scand. 2000;71:111-21.
2. Eskelinen A, Remes V, Helenius I, Pulkkinen P, Nevalainen J, Paavolainen P. Uncemented total hip arthroplasty for primary osteoarthritis in young patients: a mid- to long-term follow-up study from the Finnish Arthroplasty Register. Acta Orthop. 2006;77:57-70.
3. Benson K, Hartz AJ. A comparison of observational studies and randomized, controlled trials. N Engl J Med. 2000;342:1878-86.
4. Concato J, Shah N, Horwitz RI. Randomized, controlled trials, observational studies, and the hierarchy of research designs. N Engl J Med. 2000;342:1887-92.
5. Meier B. The evidence gap: a call for a warning system on artificial joints. New York Times. 2008 Jul 29.