Background: The purpose of this study was to evaluate the influence of image-free computer-assisted navigation\r\nsystem update on outcome in total knee arthroplasty.\r\nMethods: Thirty-three knees were replaced using the Stryker 3.1 image-free navigation system and 49 knees were\r\nreplaced using the Stryker 4.0 system. One surgeon took part in all procedures as chief surgeon or first assistant. All\r\npatients received the Stryker Scopio NRG CR total knee prosthesis. We compared the accuracy of component\r\npositioning measured using radiographs and CT scans, operating time and clinical outcome 1 year after surgery.\r\nResults: The mean hip-knee-ankle, frontal femoral and tibial component angle were 179.8�° (ideally implanted 85%),\r\n89.8�° (88%), 90.4�° (88%) respectively for the 3.1 group and 179.5�° (96%), 90.6�° (92%), 90.2�° (94%) for the 4.0 group.\r\nThe mean sagittal tibial component angle was 85.5�° (82%) for the 3.1 group and 85.6�° (92%) for the 4.0 group. The\r\nmean rotational femoral and tibial component angle were -0.5�° (81%), -0.7�° (73%) for the 3.1 group and 0.0�° (84%),\r\n0.4�° (72%) for the 4.0 group. There were no statistically significant findings with regard to component positioning.\r\nOperating time was significantly longer in the 3.1 group (3.1 group: 137 min, 4.1group: 125 min, P < 0.01).\r\nNo significant difference was detected in postoperative clinical outcome.\r\nConclusion: The navigation system update from Stryker 3.1 to Stryker 4.0 reduced operating time by 12 min.\r\nHowever, there were no statistically significant findings with regard to component positioning and clinical\r\noutcome.
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