Recutting the distal femur to increase maximal knee extension during TKA causes coronal plane laxity in mid-flexion

Background: The aim of this study was to quantify the effects of distal femoral cut height on maximal knee extension and coronal plane knee laxity. Methods: Seven fresh-frozen cadaver legs from hip-to-toe underwent a posterior stabilized TKA using a measured resection technique with a computer navigation system equipped with a robotic cutting guide. After the initial femoral resections were performed, the posterior joint capsule was sutured until a 10 degrees flexion contracture was obtained with the trial components in place. Two distal femoral recuts of +2 mm each were then subsequently made and the trials were reinserted. The navigation system was used to measure the maximum extension angle achieved and overall coronal plane laxity [in degrees] at maximum extension, 30 degrees, 60 degrees and 90 degrees of flexion. when applying a standardized varus/valgus load of 9.8 [Nm] across the knee. Results: For a 10 degree flexion contracture, performing the first distal recut of + 2 mm increased overall coronal plane laxity by approximately 4.0 degrees at 30 degrees of flexion (p = 0.002) and 1.9 degrees at 60 degrees of flexion (p = 0.126). Performing the second + 2 mm recut of the distal femur increased mid-flexion laxity by 6.4 degrees (p<0.0001) at 30 degrees and 4.0 degrees at 60 degrees of flexion (p = 0.01), compared to the 9 mm baseline resection (control). Maximum knee extension increased from 10 degrees of flexion to 6.4 degrees (+/- 2.5 degrees SD, p<0.005) and to 1.4 degrees (+/- 1.8 degrees SD, p<0.001) of flexion with each 2 mm recut of the distal femur. Conclusions: Recutting the distal femur not only increases the maximum knee extension achieved but also increases coronal plane laxity in midflexion. (C) 2012 Elsevier B.V. All rights reserved.