Tibial forces are more useful than varus-valgus laxities for identifying and correcting overstuffing in kinematically aligned total knee arthroplasty

Identifying and correcting varus-valgus (V-V) malalignment of the tibial component is important when balancing a kinematically aligned total knee arthroplasty (TKA). Accordingly, the primary objective was to determine whether the tibial forces or V-V laxities are more sensitive to, and thus more useful for identifying and correcting, V-V malalignments of the tibial component that overstuff a compartment. Calipered kinematically aligned TKA was performed on nine human cadaveric knees. Medial and lateral tibial forces and V-V laxities were measured from 0° to 120° flexion with an unmodified reference tibial component and modified tibial components that introduced ±1° and ±2° V-V malalignments from the reference component to overstuff either the medial or lateral compartment. Changes in the tibial forces were most sensitive to V-V malalignments at 0° flexion (medial = 118 ± 34 N/deg valgus malalignment and lateral = 79 ± 20 N/deg varus malalignment). The varus and valgus laxities were most sensitive to V-V malalignments at 30° flexion (−0.6 ± 0.1 deg/deg varus malalignment) and 120° flexion (−0.4 ± 0.2 deg/deg valgus malalignment), respectively. The maximum average signal-to-noise ratios of the sensitivities in tibial forces and V-V laxities (ie, signals) to reported measurement errors using current intraoperative technologies (14 N and 0.7°) (ie, noise) were 8.4 deg⁻¹ and 0.9 deg⁻¹, respectively. Because of the greater signal-to-noise ratios, measuring tibial forces is more useful than measuring V-V laxities for identifying and correcting V-V malalignments of the tibial component that overstuff a compartment. Clinical Significance: The sensitivities of tibial forces provide objective guidance to surgeons performing V-V recuts of the tibia.