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° flexion contracture was obtained with the trial components in place. Two distal femoral recuts of +2mm 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°, 60° and 90° 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 +2mm increased overall coronal plane laxity by approximately 4.0° at 30° of flexion (p=0.002) and 1.9° at 60° of flexion (p=0.126). Performing the second +2mm recut of the distal femur increased mid-flexion laxity by 6.4° (p<0.0001) at 30° and 4.0° at 60° of flexion (p=0.01), compared to the 9 mm baseline resection (control). Maximum knee extension increased from 10° of flexion to 6.4° (± 2.5° SD, p<0.005) and to 1.4° (± 1.8° SD, p<0.001) of flexion with each 2mm 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.
Hospital for Special Surgery, New York, NY 10021, USA. crossm@hss.edu
Michael B
MB
Cross
Denis
D
Nam
Christopher
C
Plaskos
Seth L
SL
Sherman
Stephen
S
Lyman
Andrew D
AD
Pearle
David J
DJ
Mayman
D000328:Adult; D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects / Q000379:methods; D002102:Cadaver; D005260:Female; D005269:Femur / Q000601:surgery*; D006801:Humans; D017746:Joint Capsule / Q000503:physiopathology / Q000601:surgery; D007593:Joint Instability / Q000209:etiology* / Q000503:physiopathology; D007719:Knee Joint / Q000503:physiopathology* / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D016059:Range of Motion, Articular / Q000502:physiology*