Letter to the Editor: 2017 Chitranjan S. Ranawat Award: Does Computer Navigation in Knee Arthroplasty Improve Functional Outcomes in Young Patients? A Randomized Study

To the Editor,

I am pleased that, after more than a decade of debate [4], Kim and colleagues [7] have demonstrated that computer assisted surgery (CAS) will not improve validated patient-reported outcome measures (PROMs) for all total knee replacement patients. The resistance to the adoption of CAS by the proponents of conventional knee replacements has finally been justified. However, we continue to report that 20% of patients remain dissatisfied following a “successful” total knee replacement. Could it be that we, as surgeons, are not catering to that 20% of the population?

If we consider the pivotal work by Belleman and colleagues [1] on anatomical variation amongst the normal population, we know that approximately 20% have a hip-knee-ankle alignment beyond the ± 3^o that is typical of the general population. Considering this, why then do we align all knees to within this target? The truth is we cannot accurately vary the degree of resection within 1^o with conventional instruments. This margin of error has led to past publications [6, 8-10] supporting the concept that total knee replacement has a higher risk of reoperation if knees are aligned outside the 3^o window of safety. Furthermore, some of these studies included poorly designed prostheses that were implanted using the mechanical alignment technique, resulting in inadvertent alignment > 3°. Therefore, it is unsurprising that during followup, these knees produced inferior PROMs and a higher risk of reoperation.

Conventional alignment targets, combined with the mechanical alignment technique and subsequent soft-tissue release to balance the knee, are applicable for 80% of the population. The use of CAS with the same surgical technique will have little impact on the overall outcome; navigation only offers surgeons the capacity for achieving the ± 3^o window more precisely. Recent studies have demonstrated the superiority of CAS over conventional instrumentation [3, 5] suggesting that assistive technologies (CAS, image-derived instrumentation, and robotics) will pave the way for superior PROMs in the future. I propose a shift in the way we look at assistive technology for total knee replacement. Importantly, these technologies are not a prescription to perform the surgery, but rather guides and tools to execute the preoperative plan.

The most promising group in which to explore the best application of CAS and other forms of assistive technologies would be those patients whose native constitutional anatomy lies outside the ± 3°. CAS technology, along with preoperative templating, may provide the surgeon the ability to predict this anatomy and to tailor the surgery to realign not only the bony anatomy but to also restore the soft-tissue envelope to its native alignment. This may have the potential to produce better PROMs for this patient subgroup. Future randomized controlled trials comparing CAS mechanical to CAS alternately aligned knees of constitutional outliers will be important to test this hypothesis and is the focus of our current work.

In summary, let’s be critical and strive to find the best application for assistive technologies in total knee replacements, as well as consider their role in addressing alignment outliers to reduce the number of patients who are dissatisfied with the results of surgery.