Background: The aim of this study was to evaluate the accuracy of initial bone cutting of the distal\nfemur and the proximal tibia in TKA using an image-free navigation system. Methods: From February\n2006 to March 2013, we evaluated 60 knees in 50 patients using an image-free navigation\nsystem (Navigation: Stryker Navigation Cart System; Software: Stryker Knee Navigation; Ver2.0:\nStryker Orthopaedics US NJ Mahwah). First, we measured the angle shown by the navigation system\nbefore cutting, at the time we set the jig. Second, we measured the angles shown by navigation\nafter the bone was cut using the jig. Then, we compared these two angles for each patient to determine\nthe bone cutting error. Results: In the distal femur, 37 of 60 knees were cut in an extended\nposition in the sagittal plane, and 26 of 60 knees were cut in a varus in the coronal plane. In the\nproximal tibia, 29 of 60 knees were cut with decreased posterior slope in the sagittal plane, and 26\nof 60 knees were cut in a valgus. Conclusions: In this study, the distal femur tended to be cut in an\nextended and a varus position and the proximal tibia did with decreased posterior slope and in a\nvalgus position after initial bone cutting. It is necessary to note the initial cutting error in TKA.\nSince cutting errors affect postoperative outcome, we should cut bones several times. And as the\nreasons of the cause of the error, we propose new reason that cutting bone is not parallel with accuracy\nto AP axis.
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