Early Radiological Outcomes of Imageless Robotic-Assisted Total Knee Arthroplasty with VELYS®: A Comparative Study of CPAK Varus vs. Valgus Phenotypes

Background: Robotic-assisted total knee arthroplasty (RATKA) offers enhanced intraoperative accuracy and real-time feedback. This study evaluates mid-term radiological outcomes of imageless RATKA in patients with mild and severe varus or valgus deformities, focusing on alignment accuracy and post-surgical outliers. Methods: A retrospective analysis was conducted on 257 patients who underwent RATKA. Demographic data, BMI, operative side, and key radiographic parameters—including pre- and postoperative hip-knee-ankle (HKA) angle, coronal alignment, joint line obliquity (MPTA + LDFA), tibial slope, and implant details—were recorded. Alignment phenotypes were classified using the CPAK system: Group 1 (varus phenotypes: CPAK I, IV, VII) and Group 2 (valgus phenotypes: CPAK III, VI, IX). Results: RATKA significantly improved alignment in both groups. In Varus Group 1 (N = 181), maximum extension improved (p < 0.001), flexion remained unchanged. JLO and HKA improved (p < 0.001). In Valgus Group 2 (N = 60), extension improved (p < 0.001) with no flexion change. Group 2 had better post-operative HKA and JLO (p < 0.001), aligning with close to CPAK 5 Neutral. Tibial resection was lower in Group 2 (7.43 ± 0.96) mm vs. (8.68 ± 1.45 mm). One tibial recut and one revision observed. Liner use favored 5 mm (80.11%) in Group 1, (90%) in Group 2. RATKA effectively optimized alignment and minimized tibial resection in valgus and varus deformities. Conclusion: Imageless RATKA provides accurate alignment correction in both varus and valgus deformities, even in severe cases. It enables minimal tibial resection and precise, balanced placement of cruciate-retaining implants, underscoring its role in optimizing modern TKA outcomes.