Under-Corrected but Not Underperforming: Residual Varus Does Not Compromise Early Outcomes After Robotic rKA TKA in Severe Varus Knees

Abstract Background : Kinematic alignment (KA) in total knee arthroplasty (TKA) aims to restore native joint-line orientation and preserve ligament balance. However, implant design limits tibial varus correction to approximately 7°, potentially preventing full anatomical restoration in patients with severe tibial varus deformity (MPTA < 83°). This study compared radiographic and clinical outcomes following robotic-assisted restricted KA (rKA) TKA in patients with severe versus moderate tibial varus. Methods : A retrospective cohort study was conducted on 140 consecutive patients undergoing imageless robotic-assisted rKA TKA between January 2024 and April 2025. Patients were stratified into MPTA < 83° (n = 40) and MPTA ≥ 83° (n = 100) groups. All procedures used the VELYS robotic platform with a cemented cruciate-retaining ATTUNE prosthesis. Postoperative radiographic parameters (MPTA, LDFA, aHKA) and patient-reported outcome measures (KSFS, KSKS, OKS, SF-36 PCS/MCS) were assessed preoperatively and at 6 months. Day-one pain, ambulation distance, and range of motion were also evaluated. Minimal clinically important difference (MCID) achievement was analysed. Results : Patients with MPTA < 83° had significantly greater preoperative varus deformity (− 8.1 ± 4.1° vs − 4.2 ± 2.3°, p < 0.001). Postoperatively, this group demonstrated lower MPTA (83.4 ± 2.5° vs 85.0 ± 2.5°, p = 0.005), greater residual varus (aHKA − 5.8 ± 4.6° vs − 3.2 ± 4.5°, p = 0.003), and lower rates of restoration of native MPTA (20% vs 70%, p < 0.001) and CPAK phenotype (20% vs 61%, p < 0.001). Despite this, both groups showed significant improvement across most functional outcomes with no significant between-group differences in change scores, MCID achievement, satisfaction, or expectation fulfilment at 6 months. Conclusion : Patients with severe tibial varus undergoing robotic rKA TKA achieved comparable short-term functional outcomes despite incomplete restoration of native alignment. These findings suggest that ligament balance and preservation of native kinematics may be more important determinants of early outcomes than complete radiographic correction.