ROSA™ Imageless Robotic-Assisted Conversion from Unicompartmental to Total Knee Arthroplasty: A Novel Surgical Technique and Case Report

Background: Unicompartmental knee arthroplasty (UKA) is an effective treatment for isolated compartment knee osteoarthritis, but it is associated with a higher risk of revisions. UKA-to-TKA conversions remain surgically challenging. In particular, the restoration of correct femoral rotation is difficult, mainly because of bone loss and altered anatomical landmarks. We describe a novel imageless robotic-assisted technique for UKA-to-TKA conversion using the ROSA™ robotic system and report a representative clinical case. Methods: After a standard medial parapatellar approach and joint exposure, the landmarks are registered with the UKA in situ, followed by the standard workflow for a robotic-assisted primary TKA according to the “inverse functional alignment” philosophy (virtual planning, tibial cut, planning adjustment, distal femoral cut and planning adjustment). At last, the femoral component rotation is defined using the FuZion® tensioner, with the UKA femoral component being left in situ to compensate for the lateral posterior condyle bone loss. Results: A 72-year-old female patient underwent robotic-assisted lateral UKA-to-TKA conversion due to aseptic loosening of the tibial component. Accurate bone resection, restoration of alignment, and soft tissue balancing were achieved, avoiding the use of augments. Postoperative recovery was uneventful, with satisfactory clinical and functional outcomes at 3-month follow-up. Conclusions: Imageless robotic-assisted UKA-to-TKA conversion using the ROSA™ system seems a valuable aid in these complex scenarios. To our knowledge, this is the second report describing this procedure using the ROSA™ robot and the first presenting a distinct surgical technique. Further studies on larger cohorts are needed to confirm this technique efficacy and possible limitations.