Image-based robotic-assisted conversion from partial to total knee arthroplasty under functional alignment: Comparable outcomes to primary total knee arthroplasty

Introduction: Image-based robotic systems in total knee arthroplasty (TKA) allow for precise implant positioning and soft tissue balance through patient-specific preoperative planning. Functional alignment (FA) leverages the native soft tissue envelope to guide implant placement. However, its application in partial TKA conversion remains limited. This study evaluates the outcomes of image-based robotic-assisted partial-to-TKA conversion under FA principles, comparing them to a cohort of primary robotic TKAs. Methods: This retrospective study analyzed eight partial-to-TKA conversions performed using the image-based robotic system, with a minimum follow-up of 12 months. Demographics, implant constraints, intraoperative positioning, and postoperative outcomes were assessed. The mean age of the revision cohort was 73.3 ± 9.0 years, with a mean follow-up of 39.0 ± 11.5 months. A control group of 50 primary robotic TKAs was used for comparison. Results: Osteoarthritis progression (75%) and aseptic loosening (25%) were the primary reasons for revision. No stems were used, and only one patient (12.5%) required a tibial augment. Postoperative coronal alignment was 1.1° ± 1.9°, and functional outcomes (Knee Society Score-Knee: 84.5 ± 6.7, Knee Society Score-Function: 83.0 ± 7.1, Forgotten Joint Score: 72.8 ± 8.2) were comparable to the primary TKA cohort. No complications or revisions were recorded. Conclusion: FA-based robotic-assisted partial-to-TKA conversion yields functional and implant positioning outcomes comparable to primary robotic TKA while minimizing the need for stems, augments, or constrained implants. Further studies with larger cohorts are needed to confirm these findings. Level of evidence: III.