Patient specific variables impact sensitivity to association between joint balance and 2 Year outcomes.

Background: This study investigates the association between intra-operative balance and 2-year outcomes within subgroups defined by demographics and pre-operative joint balance. Our hypothesis is that patient demographics and the pre-operative state of the joint will impact patient sensitivity to post-operative balance and laxity and subsequent impact on outcome.

Methods: A retrospective analysis of prospectively captured data across 5 sites with 5 surgeons was performed. All cases completed pre-operative demographics surveys, 2-year post-operative Knee Injury and Osteoarthritis Outcome Score (KOOS) and had a robot assisted total knee arthroplasty with an integrated digital joint balancing tool. Differences in associations between intra-operative final joint balance and 2-year KOOS pain outcomes in demographic and pre-operative balance subgroups were characterized. Associations informed clinically relevant thresholds to optimize TKA treatment for subgroups.

Results: A total of 276 patients completed 2-year KOOS scores. Subgroups were defined from Sex, Age, BMI and pre-operative extension laxity. Men prefer a tight tolerance medially in extension and mid-flexion while females prefer a tight lateral flexion gap. Patients <70 years show a strong preference for equal rectangular gaps in extension, mid-flexion, and flexion, while older patients do not show a preference. Patients with BMI ≤30 demonstrate a preference for rectangular gaps, while patients with higher BMI do not. Finally, patients with looser pre-operative extension laxity (>3 mm) preferred a TKA with increased extension laxity compared to patients with minimal preoperative laxity.

Conclusion: Intraoperative differences in knee balance can influence patient outcome scores among different demographic groups at two years postoperatively. This suggests further research is warranted to determine how ligament balance and laxity may be optimized based on individual patient factors.