CORR Insights®: Does Robotic-assisted TKA Result in Better Outcome Scores or Long-Term Survivorship Than Conventional TKA? A Randomized, Controlled Trial

摘要

Where Are We Now? In my experience, a successful total knee replacement is determined by implant positioning, leg alignment, and soft-tissue balance, which includes medial-lateral and AP stability. My definition of a well-done TKA has not changed since the early 1980s, when our specialty—and patients’ lives—were improved by the development of precision mechanical alignment guides, and by the tireless work of David S. Hungerford MD who taught surgeons how to use them. The principles of successful rotational alignment of the implants, and soft-tissue treatment and balance were taught by Chitranjan S. Ranawat MD, and John N. Insall MD for posterior cruciate ligament sacrificing knees, and Richard D. Scott MD and Tom S. Thornhill MD for posterior-cruciate ligament retaining knees. These principles of total knee replacement have not appreciably changed through four decades, nor has implant design resulted in anything other than evolutionary change. The authors of the current study do not change the principles of the operation, but describe more-precise instrumentation, specifically for the bone cuts in the coronal plane [4]. Since the success of total knee replacement is dependent on rotational mating of the femoral and tibial implants, and the soft-tissue balance of the knee, both of which remain dependent on surgeon decisions no matter the instrumentation, it is unreasonable to expect a difference in clinical scores or revisions between a surgeon who performed 340 total knee replacements per year (as did the surgeon in this study) and the use of high-tech instruments. Indeed, no difference was found. But that does not mean that robotic instrumentation offers no value to low volume or inexperienced surgeons. Where Do We Need To Go? We are still trying to find answers for the 25% or so of patients who are not happy with the results of their total knee replacements. To achieve what some have termed the “forgotten knee” (a knee replacement so good that the patient forgets (s)he has undergone the procedure), I believe the operation needs to be personalized for each patient. Unfortunately, as yet, surgeons haven’t figured out just how to do that effectively. We have learned that malalignment of the knee, either in the coronal plane > 3° or rotationally, can cause pain [5]. A second clinical cause of pain is malrotation of the femoral component to the tibia, which commonly causes anteroposterior instability, again increasing strain on capsule and ligaments. Medial-lateral instability can come from incorrect bone cuts (so the medial and lateral compartments or the flexion-extension gaps are not balanced) and/or insufficient knee alignment (which can result is ligamentous imbalance) or polyethylene thickness. A stiff knee may occur when the surgeon makes choices that result in a tight knee with respect to soft-tissue balance, including insufficient releases or use of a a polyethylene bearing that is too thick. If we combine all of these known causes, only coronal and rotational bone cuts can potentially improve instrumentation, while the soft-tissue balance is under the surgeon’s control. There is also controversy regarding the limits of coronal alignment. For example, 26% of the knees in the current study are considered outliers, as they have a mechanical axis of +/- 3° using conventional instruments. This drops to 6% if we consider an outlier to be +/- 5°. But we don’t know the limits of outlier alignment before pain or dissatisfaction with alignment becomes statistically relevant. Just because these authors decreased the percentage they considered outliers to 5°, that does not mean that knees at that malalignment should be acceptable. A recent study [1] found no difference in the frequency of revision between knees neutrally aligned and outliers +\- 3° 20 years post-operation. By contrast, a study using radiostereometric analysis to measure migration found increased loosening in knees that were +\- 3° outliers [6]. It’s clear that we h