Navigation system
Our navigation system (Orthomap Express, Stryker, Michigan) is an image-free navigation system. No preoperative image is required. The anatomical morphology of knee is registered during operation. This system uses wireless optical tracking technology. Infrared light emitted by diodes placed on navigated surgical instruments is sensed by a camera array (navigation camera) on the computer platform. No need for tracker pins in femur and tibia shafts. The navigation system was only used for distal femur cutting and verification for the resection level in this study. Because the tibia cutting jig of Orthomap Express was much larger than that of MIS instrument, we used the MIS instrument for proximal tibia cut to reduce wound length discrepancy between the two groups.