Editor's Spotlight/Take 5: The Chitranjan S. Ranawat Award: No Difference in 2-year Functional Outcomes Using Kinematic versus Mechanical Alignment in TKA: A Randomized Controlled Clinical Trial

Abstract

For many years, there had been little argument about how to align a TKA: Put the center of the knee under the center of the hip and over the center of the ankle. More recently, though, the concept of kinematic alignment has garnered more attention. Kinematic TKA alignment seeks to restore the “prearthritic” anatomy of a patient's knee, typically providing for a bit of residual tibial varus and femoral valgus compared to what surgeons used to mechanical-axis alignment might aim for. The rationale for this approach is that it may more-closely replicate the dynamic function of a normal knee, perhaps decreasing the need for soft-tissue releases; some work suggests kinematic TKA alignment may be associated with better scores for pain and function [2, 3]. This set of potential benefits may come at a cost. Many (though not all [3]) studies on kinematic alignment use patient-specific guides, which generally are more expensive. And leaving tibial components in varus (as is commonly done with kinematic alignment) may result in a higher risk of aseptic loosening over time. An award-winning paper from this year's Knee Society Proceedings by Bill Farrington's group at North Shore Hospital in Auckland, New Zealand, took a careful look at kinematic and mechanical-axis alignment, comparing them in a well-designed randomized trial. In short summary, they found no differences in Oxford Knee Scores, WOMAC scores, or complications between these surgical approaches at 2 years. Given the costs and uncertainty associated with kinematic alignment, this work would seem to put the ball deeply into the court of those who wish to justify the use of that approach. This paper is important even if one does not perform TKA, since it provides an aspirational standard for investigators who wish to answer important research questions in any discipline within orthopaedic surgery. The authors defined a clinically important difference (five points on the Oxford score), powered the study to detect this difference, and accounted for all of their patients. They reported a set of no-difference conclusions; doing so is critically important [4]. They present the no-difference findings with modesty and clarity, and ask fair questions about the risks associated with a technique they explored. This is exactly the kind of work that should inform our practices. Although this randomized trial is at odds with an earlier randomized study on the topic that favored kinematic alignment [1], Mr. Farrington's work provides plausible explanations for this difference and seems (at least to me) more generalizable than that earlier report [1]. It is fair to say that the book is far from closed on kinematic alignment. But this study gives knee surgeons a reason to think twice before adopting this bit of surgical novelty. Please join me as I go behind the discovery with Mr. Farrington, senior author of “The Chitranjan S. Ranawat Award: No Difference in 2-year Functional Outcomes Using Kinematic versus Mechanical Alignment in TKA: A Randomized Controlled Clinical Trial,” about new technology, issues associated with discovering and reporting no-difference results, and what it takes to perform a well-controlled randomized trial. Take Five Interview with Bill Farrington FRCS, FRACS, senior author of “The Chitranjan S. Ranawat Award: No Difference in 2-year Functional Outcomes Using Kinematic versus Mechanical Alignment in TKA: A Randomized Controlled Clinical Trial” Seth S. Leopold MD:Congratulations on publishing this well-designed and well-executed randomized trial, and also on your prestigious Knee Society award. Would you be willing to share your feelings about the two surgical approaches as they were prior to the start of this study, and how your feelings changed once you analyzed the results? Bill Farrington FRCS, FRACS: Thank you, Seth. It was a pleasant surprise and we feel greatly honored by the award. In 2011, my colleagues and I first heard about kinematic alignment (KA) and we wer