Modified gap-balancing technique in total knee arthroplasty: evaluation of the post-operative coronal laxity.

It is unknown how intra-operative soft-tissue balance affects post-operative knee kinematics during different functional tasks. In order to clarify this relationship, the intra-operative varus-valgus balance and post-operative knee kinematics were compared for 17 patients who underwent total knee arthroplasty using a modified gap technique. The intra-operative balance was recorded with a tensor device, and in vivo knee kinematics of lunging, kneeling and non-weight-bearing knee extension were analyzed with 3D-to-2D model registration techniques. Femoral condylar separation from the tibial articular surface also was investigated. The post-operative varus-valgus angle in 90 degrees kneeling had a strong relationship with the intra-operative varus-valgus angle, while there was a weak relationship for the non-weight-bearing motion at 0 degrees and 90 degrees flexion. Articular surface separation was an uncommon observation, seen in 2.2% of images during non-weight-bearing motion and in none of the lunging or kneeling images. The modified gap technique appears effective providing stable knee arthroplasty kinematics during in vivo activities with minimal articular separation in non-weight-bearing motion.