More Precision, So Greater TKA Longevity? Not Yet

Commentary Providing patients with a well-functioning, durable, and satisfactory knee prosthesis is the end goal in the current “arms race” occurring in the field of total knee arthroplasty (TKA). It has been widely accepted that accurate bone resection and precise implant positioning are critical to the overall success of the surgical technique. To address the limitations of conventional measured resection and gap balancing strategies with manual instruments, advanced technologies to assist in TKA, primarily computer navigation and patient-specific instrumentation (PSI), have emerged. For these technologies to gain acceptance in modern clinical practice, they must demonstrate either (1) superior efficacy to existing methods or (2) similar outcomes at a lower cost. While numerous studies indicate that these technologies substantially improve implant and limb alignment compared with conventional TKA, there remains no consensus on their effects on functional outcomes and longevity1,2. Consequently, these technologies appear to provide surgeons with aesthetically pleasing postoperative radiographs without delivering tangible benefits to patients. There appears to be no evidence that the increased costs of these technologies can be offset by savings from reduced revision rates, which may explain the reluctance of many surgeons and hospital administrators to adopt them. Farhan-Alanie et al. have made a crucial contribution to this area by analyzing real-world data from the National Joint Registry (NJR) in the U.K. spanning nearly 2 decades and >1 million procedures. They found that, over the follow-up period, the risk (assessed with hazard ratios) for all-cause revision following TKA using either computer navigation or PSI did not differ significantly compared with that for conventional instrumentation. No differences were observed in the Oxford Knee Score, EQ-5D-3L score, and mortality within 1 year postoperatively between conventional TKA and TKA with computer navigation or PSI. By using propensity scoring to account for multiple covariates, the authors enhanced the reliability of their findings, highlighting that the expected benefits of these technologies may not be evident in real-world settings. This study serves as a vital reminder for clinicians to thoroughly evaluate the adoption of such technologies, especially when their justification relies on presumed improvements in patient functional outcomes and longevity. It is important to interpret the results with the study’s limitations in mind. First, as noted by the authors, the power of at best 0.69 for detecting a hazard ratio of 0.90 raises the risk of false negatives. Since the study groups were unequal in size and the observed hazard ratios exceeded 0.90, the analyses were somewhat underpowered to detect differences of such a size in revision rates between conventional and computer-navigated surgery. Second, around 30% of TKA procedures in the NJR data set lacked body mass index (BMI) data. Although the authors addressed the impact of missing data through sensitivity analyses, non-random missingness of data for specific clinical or demographic factors (e.g., BMI) could introduce bias, affecting later comparisons of all-cause revision and PROMs. Lastly, functional scores were assessed at 6 months postoperatively, which does not reflect early or long-term functional status. In the 1980s, Professor John Insall stated that “TKA is primarily a soft tissue operation,” highlighting the importance of managing soft tissues to achieve balance in classic mechanical-axis alignment strategies3. Four decades later, this principle remains vital for orthopaedic surgeons, but there has been a shift toward minimizing soft-tissue irritation during TKA procedures through various alignment strategies and the use of surgical-assistance technologies, such as robotics, in order to improve patient function and satisfaction. This presents challenges in computer navigation and PSI use. Additionally, with the development of modern highly cross-linked polyethylene and advancements in materials facilitating bone ingrowth and cement techniques, several long-term follow-up studies have indicated that implant survivorship in the so-called outlier group (lower-limb alignment of ±3° or more ) does not significantly differ from neutral mechanical alignment4. This reality compels modern surgeons to weigh the cost-effectiveness of adopting technologies that primarily serve the functions of precise bone resection and implant positioning. In summary, Everett Rogers’ “diffusion of innovations” theory5 classifies technology adopters as innovators, early adopters, early majority, late majority, and laggards, with the adoption process depicted by a bell curve. Currently, computer-navigated TKA and PSI remain in the “early adopter” phase. We need to rethink our evaluation methods, and perhaps better assessment approaches in the future will reveal the true benefits that these technologies offer to patients. However, for now, we still rely on high-quality long-term follow-up results to guide our clinical decisions.