To the Editor,
We thank Koster et al. for their letter and for the positive feedback regarding our work. We agree that radiostereometric analysis (RSA) is an excellent tool for detecting small implant movements and providing a more-graduated outcome measure compared with the all-or-nothing outcome of revision. This feature of RSA may allow greater insight into functional relationships between surgeon-controlled factors and risk of revision and accelerate the time required to draw conclusions, which can be extremely valuable.
As Koster et al. point out, RSA can be particularly effective when investigating questions involving larger effect sizes. An example of this would be the difference in mean migration associated with Boneloc (Biomet Inc) bone cement [2]. However, if we are investigating effects that are relatively subtle (such as the influence of tightened alignment precision on the fractions of patients who experience significant implant migration), then using RSA likely wouldn't markedly reduce the number of patients who would need to be studied, which, as we have shown, can be impractically large. As Koster et al. note, previous studies [1, 2] failed to find any notable differences when enrolling less than 100 patients. While it is possible that no major difference exists, it is also plausible that these studies were simply underpowered, despite using RSA. Additionally, since performing RSA analysis requires an additional operative step and postoperative biplanar scans, it would likely continue to be impractical to design a clinical study to measure differences in revision rates attributable to technology assistance, even if by using RSA we could reach those conclusions much sooner than by waiting to observe revisions.
Therefore, while we agree with the letter writers that RSA should be more widely used to rapidly check for potentially catastrophic effects when new implants or surgical techniques are introduced, RSA is unlikely to markedly reduce the study size needed to detect more subtle effects such as a modest difference in revision rates.
Footnotes
(RE: Koster LA, Kaptein BL, Pijls BG, Nelissen RGHH. Letter to the Editor: How Large a Study is Needed to Detect TKA Revision Rate Reductions Attributable to Robotic or Navigated Technologies? A Simulation-based Power Analysis. Clin Orthop Relat Res. Published online. DOI: 10.1097/CORR.0000000000002123.)
The institution of one or more of the authors (MDH, AJH) has received funding from the Natural Sciences and Engineering Research Council of Canada. One of the authors (CA) certifies that she is President of and holds stock/stock options in Ammolite BioModels and holds several patents relevant to the work. One of the authors (BM) certifies receipt of personal payments or benefits, during the study period, in an amount of less than USD 10,000 from Stryker, as well as research support from Zimmer, Smith & Nephew, DePuy, and Stryker. One of the authors (AJH) certifies that he holds shares in Traumis Surgical Systems and holds several patents (US9554812, US8548559, US10010381, and US9037295) that are broadly relevant to the work.
All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research® editors and board members are on file with the publication and can be viewed on request.
The opinions expressed are those of the writer, and do not reflect the opinion or policy of CORR® or The Association of Bone and Joint Surgeons®.
Contributor Information
Carolyn Anglin, Email: carolyn.anglin@gmail.com.
Bassam Masri, Email: bas.masri@ubc.ca.
Antony J. Hodgson, Email: ahodgson@mech.ubc.ca.
References
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