• Shota Mitsuhashi, Yasushi Akamatsu, Hideo Kobayashi, Yoshihiro Kusayama, Ken Kumagai, and Tomoyuki Saito.
• Department of Orthopaedic Surgery, Yokohama City University School of Medicine, 3-9 Fukuura, kanazawa-ku, Yokohama, 236-0004, Japan. t156069e@yokohama-cu.ac.jp.
• Arch Orthop Trauma Surg. 2018 Feb 1; 138 (2): 259-266.

IntroductionRotational malpositioning of the tibial component can lead to poor functional outcome in TKA. Although various surgical techniques have been proposed, precise rotational placement of the tibial component was difficult to accomplish even with the use of a navigation system. The purpose of this study is to assess whether combined CT-based and image-free navigation systems replicate accurately the rotational alignment of tibial component that was preoperatively planned on CT, compared with the conventional method.Materials And MethodsWe compared the number of outliers for rotational alignment of the tibial component using combined CT-based and image-free navigation systems (navigated group) with those of conventional method (conventional group). Seventy-two TKAs were performed between May 2012 and December 2014. In the navigated group, the anteroposterior axis was prepared using CT-based navigation system and the tibial component was positioned under control of the navigation. In the conventional group, the tibial component was placed with reference to the Akagi line that was determined visually. Fisher's exact probability test was performed to evaluate the results.ResultsThere was a significant difference between the two groups with regard to the number of outliers: 3 outliers in the navigated group compared with 12 outliers in the conventional group (P < 0.01).ConclusionsWe concluded that combined CT-based and image-free navigation systems decreased the number of rotational outliers of tibial component, and was helpful for the replication of the accurate rotational alignment of the tibial component that was preoperatively planned.

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