The Accuracy of Initial Bone Cutting in Total Knee Arthroplasty

Background: The aim of this study was to evaluate the accuracy of initial bone cutting of the distal femur and the proximal tibia in TKA using an image-free navigation system. Methods: From February 2006 to March 2013, we evaluated 60 knees in 50 patients using an image-free navigation system (Navigation: Stryker Navigation Cart System; Software: Stryker Knee Navigation; Ver2.0: Stryker Orthopaedics US NJ Mahwah). First, we measured the angle shown by the navigation system before cutting, at the time we set the jig. Second, we measured the angles shown by navigation after the bone was cut using the jig. Then, we compared these two angles for each patient to determine the bone cutting error. Results: In the distal femur, 37 of 60 knees were cut in an extended position in the sagittal plane, and 26 of 60 knees were cut in a varus in the coronal plane. In the proximal tibia, 29 of 60 knees were cut with decreased posterior slope in the sagittal plane, and 26 of 60 knees were cut in a valgus. Conclusions: In this study, the distal femur tended to be cut in an extended and a varus position and the proximal tibia did with decreased posterior slope and in a valgus position after initial bone cutting. It is necessary to note the initial cutting error in TKA. Since cutting errors affect postoperative outcome, we should cut bones several times. And as the reasons of the cause of the error, we propose new reason that cutting bone is not parallel with accuracy to AP axis.