Bone resection for mechanically aligned total knee arthroplasty creates frequent gap modifications and imbalances

Purpose The objective of this study was to calculate bone resection thicknesses and resulting gap sizes, simulating a measured resection mechanical alignment (MA) technique for total knee arthroplasty (TKA). Methods MA bone resections were simulated on 1000 consecutive lower limb CT scans from patients undergoing TKA. Femoral rotation was aligned with either the surgical trans-epicondylar axis (TEA) or with 3° of external rotation to the posterior condyles (PC). Imbalances in the extension space, flexion space, medial compartment and lateral compartment were calculated. Results Extension space imbalances (≥ 3 mm) occurred in 25% of varus and 54% of valgus knees and severe imbalances (≥ 5 mm) were present in up to 8% of varus and 19% of valgus knees. Higher flexion space imbalance rates were created with TEA versus PC ( p