Standardized Intraoperative Robotic Laxity Assessment in TKA Leads to No Clinically Important Improvements at 2 Years Postoperatively: A Randomized Controlled Trial

BACKGROUND: Joint stability is a major factor associated with success after TKA. However, most assistive technologies, such as robotic-assisted TKA, do not incorporate a standardized laxity assessment. To address this gap, we opted to perform a randomized controlled trial comparing the results of a manual versus a robot-assisted TKA system with standardized laxity assessment. QUESTIONS/PURPOSES: (1) Does robot-assisted TKA with a standardized laxity assessment provide superior patient-reported outcomes compared with conventional TKA with a manual tensioner, and does it result in a higher percentage of patients achieving the patient acceptable symptom state (PASS) thresholds 2 years after surgery? (2) Does robot-assisted TKA with a standardized laxity assessment provide different coronal alignment or coronal laxity compared with conventional TKA with a manual tensioner after surgery? METHODS: This was a prospectively registered randomized trial performed at a single center in Belgium. Patients with end-stage knee osteoarthritis unresponsive to conservative treatment were eligible. Exclusion criteria included severe deformity, limited ROM, prior fractures, infection, ligament insufficiency, and neurologic conditions. Between September 2020 and August 2022, we randomized 60 patients to receive TKA either with a manual tensiometer (n = 30) or a robotic-assisted TKA with an imageless system using a standardized laxity system (distraction of the tibiofemoral joint with 80N throughout ROM; n = 30). Of those, 100% (30 of 30) and 90% (27 of 30) of patients were available for follow-up at 2 years in the robotic-assisted and conventional groups, respectively. In both groups, a posterior stabilized implant was used. Patient-reported outcome measures (Knee Society Score [KSS], WOMAC, and 5-level EuroQol 5-domain scores) were obtained preoperatively and at 2 years postoperatively. Coronal alignment and implant position were evaluated on full-leg weightbearing radiographs. Stress radiographs were obtained to assess coronal laxity in 10° of flexion. There were no differences between the groups in baseline characteristics of age, BMI, side, gender, hip-knee-ankle axis, ROM, or patient-reported outcome measures. To account for multiple comparisons in this study, a Bonferroni correction was applied. All differences between both groups were evaluated considering minimum clinically important difference values for patients who have undergone TKA. The power analysis indicated 80% power to detect a clinically meaningful difference of 9.7 points in KSS function score, with an alpha of 0.05. RESULTS: We found no clinically important differences in patient-reported outcomes 2 years after surgery between the conventional and the robotic group (for example, the KSS function score in those groups was 66 ± 20 versus 74 ± 24, respectively, mean difference 8 [95% confidence interval (CI) -3 to 21]; p = 0.18), and no difference in the proportion of patients in those groups who achieved the PASS on any outcomes score (for example, the percentage of patients achieving the PASS for the WOMAC was 4% [1 of 27] versus 3% [1 of 30], respectively, OR 0.9 [95% CI 0 to 15]; p > 0.99). Likewise, there were no differences in postoperative hip-knee-ankle axis between the conventional and the robotic groups, respectively (1° ± 2° varus versus 1° ± 3° varus; p > 0.99) or in coronal-plane laxity (6° ± 3° versus 7° ± 2° in the conventional cohort; p = 0.73). CONCLUSION: Based on the absence of clinically important differences in outcome scores or any differences in the proportion of patients who achieved the PASS on those scores (as well as the absence of meaningful differences in alignment or soft tissue tension), we recommend against the routine use of robotic TKA with objectified laxity assessment because it adds costs and time to these procedures without delivering benefits that patients might perceive. Future studies might, however, be able to identify patient-specific laxity targets to improve patient outcomes. LEVEL OF EVIDENCE: Level I, therapeutic study.