Does Restoration of Constitutional Alignment Improve Outcomes in Total Knee Arthroplasty?

Background: While neutral mechanical alignment has been the gold standard for total knee arthroplasty (TKA), constitutional knee alignment is commonly nonneutral and varies widely among individuals. We aimed to determine if a bounded functional alignment strategy in robotic assisted TKA restored constitutional alignment and if this restoration resulted in superior patient-reported outcomes (PROs). Methods: We retrospectively reviewed patients who underwent robotic TKA with a bounded functional alignment strategy at a single institution. Final intraoperative knee alignment was compared to calculated constitutional alignment, which was unknown to the surgeons during the procedure. PROs (Knee injury and Osteoarthritis Outcome Score for Joint Replacement and Patient-Reported Outcomes Measurement Information System) with a 1-year follow-up were compared between patients with a final knee alignment within 2° of constitutional alignment compared with those >2° from calculated constitutional alignment. Mean changes in PROs were analyzed, and proportions achieving minimally clinical important difference between groups was determined. Results: Of the 188 knees included, 52% (n = 98) were balanced within 2° of constitutional alignment. Despite significant differences in alignment changes between groups (2.0° vs 4.5°), no significant differences were observed in PRO measures. Mean Knee injury and Osteoarthritis Outcome Score for Joint Replacement improvement (25.0 vs 29.5), Patient-Reported Outcomes Measurement Information System Physical Health (8.0 vs 7.7), and Mental Health (2.7 vs 1.2) scores were comparable. Similar proportions in both groups achieved minimally clinical important difference across all measures. Conclusions: While robotic bounded functional strategy restored constitutional alignment in half of cases, this did not result in superior PROs at 1 year. Achieving soft tissue balance within acceptable parameters of alignment and bony excision may be more important than precise restoration of prearthritic alignment.