• Kazunori Hino, Tatsuhiko Kutsuna, Kunihiko Watamori, Hiroshi Kiyomatsu, Yasumitsu Ishimaru, Jun Takeba, Seiji Watanabe, Yoshitaka Shiraishi, and Hiromasa Miura.
• Department of Orthopaedic Surgery, Ehime University Graduate School of Medicine, Shitsukawa, Toon, Ehime, 790-0295, Japan. taimisaki@gmail.com.
• Arch Orthop Trauma Surg. 2017 Oct 1; 137 (10): 1429-1434.

IntroductionMidflexion stability can potentially improve the outcome of total knee arthroplasty (TKA). The purpose of this study was to evaluate the correlation between varus-valgus stability at 0° of extension and 90° of flexion and that at the midflexion range in posterior-stabilized (PS)-TKA.Materials And MethodsForty-three knees that underwent PS-TKA were evaluated. Manual mild passive varus-valgus stress was applied to the knees, and the postoperative maximum varus-valgus stability was measured every 10° throughout range of motion, using a navigation system. Correlations between the stability at 0°, 90° of flexion, and that at each midflexion angle were evaluated using Spearman's correlation coefficients.ResultsThe stability of 0° modestly correlated with that of 10°-20°, but it did not significantly correlate with that of 30°-80°. However, the stability of 90° strongly correlated with that of 60°-80°, modestly correlated with that of 40°-50°, weakly correlated with that of 20°-30°, and did not correlate with that of 10°.ConclusionsThe present study confirmed the importance of acquiring stability at 90° flexion to achieve midflexion stability in PS-TKA. However, initial flexion stability did not strongly correlate with the stability at either 0° or 90°. Our findings can provide useful information for understanding varus-valgus stability throughout the range of motion in PS-TKA. Attention to soft tissue balancing is necessary to stabilize a knee at the initial flexion range in PS-TKA.

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