Abstract / Summary
Abstract Purpose. The varus knee is medially tight and has classically been balanced by stepwise soft-tissue release, which risks over-release. We tested whether, in functional-alignment (FA) robotic total knee arthroplasty (TKA), femoral rotation titrated to the medial gap balances the varus knee to within one millimetre with only a mild release, and derived a bedside rule. Methods. Observational analysis of 65 consecutive varus primary FA robotic TKAs by a single surgeon using an image-based platform. Femoral rotation, medial–lateral (M–L) gap asymmetry across preoperative, planned and final states, the graded release and balance were analysed; regression related rotation to medial flexion tightness; Wilson 95% confidence intervals; no imputation. Results. Femoral external rotation was titrated to the medial flexion gap — approximately 1.9° plus 0.34° per millimetre of tightness (ρ = −0.57; R² = 0.26; p < 0.001) — giving a simple bedside rule. With this, the medial release stayed mild in 64/65 knees (no escalation). M–L asymmetry fell from 3.8/4.5 mm (extension/flexion) to 0.4/0.3 mm — below one millimetre in 83%/93% of knees — mostly by planning. Functional balance reached 98% and strict-mechanical balance 91%; WOMAC improved from 74.6 to 2.5 and FJS-12 reached 95.2 at one year. Conclusion. In the varus knee, rotating the femur to the medial gap — rather than releasing more soft tissue — balances the knee to within one millimetre with only a mild release. A simple titration chart and playbook translate this into daily practice.