Intentional asymmetric balancing in robotic-assisted valgus TKA: Early outcomes and intraoperative laxity changes

To evaluate early patient-reported outcome measures (PROMs), radiographic alignment changes, intraoperative laxity changes and complications in a retrospective series of constitutional valgus knees treated with robotic-assisted total knee arthroplasty (TKA) using an intentional asymmetric balancing strategy and a semi-personalized (SP) alignment technique.

This retrospective single-centre cohort included consecutive patients with end-stage valgus osteoarthritis (OA) and constitutional valgus morphotypes (coronal plane alignment of the knee III/VI) treated with imageless robotic-assisted TKA and a minimum follow-up of 12 months. The balancing workflow intentionally accepted mild residual lateral laxity. Medial and lateral compartment laxity (mm) were quantified intraoperatively at 0° and 90°. PROMs (Knee Society Score [KSS] and Forgotten Joint Score [FJS]), range of motion (ROM) and hip-knee-ankle angle (HKA) were assessed preoperatively and at the latest follow-up. Complications were recorded.

Fifty-eight patients were included at a mean follow-up of 26.5 ± 15.0 months. KSS Knee improved from 58.3 ± 9.4 to 87.9 ± 11.0 (mean change +29.6 points, 95% confidence interval [CI] = 26.0-33.2; p = 0.00002) and KSS Function from 58.8 ± 15.0 to 82.4 ± 15.7 (mean change +23.6 points, 95% CI = 18.8-28.4; p = 0.00004). Flexion contracture improved from 3.9 ± 4.0° to 0.6 ± 1.2° (mean change -3.3°, 95% CI = -4.3 to -2.3; p = 0.00010), while flexion increased from 101.4 ± 6.0° to 126.8 ± 8.6° (mean change +25.4°, 95% CI = 23.2-27.6; p = 0.00001). HKA improved from 6.2 ± 4.5° valgus to 2.1 ± 1.8° valgus (mean change -4.1°, 95% CI = -5.2 to -3.0; p = 0.00030). Lateral laxity decreased in extension from 4.5 ± 1.7 to 2.5 ± 1.3 mm (mean change -2.0 mm, 95% CI = -2.7 to -1.3; p = 0.001) and at 90° from 5.3 ± 2.0 to 1.9 ± 1.2 mm (mean change -3.4 mm, 95% CI = -4.3 to -2.5; p = 0.0008), with smaller medial reductions. Post-operative complications occurred in four patients (6.9%) (deep vein thrombosis, transient peroneal neuropraxia, superficial wound issue and one manipulation under anaesthesia); there were no pulmonary emboli, periprosthetic joint infection or revision procedures.

In this retrospective single-surgeon series of constitutional valgus knees treated with robotic-assisted TKA, intentional asymmetric balancing was associated with good early clinical outcomes, correction towards less valgus alignment, and a reproducible reduction in lateral laxity, with a low complication rate. These findings support the feasibility of this measurable laxity-guided strategy, but do not establish superiority over alternative balancing philosophies.

Level III, retrospective cohort.