Varus–valgus stability at 90° flexion correlates with the stability at midflexion range more widely than that at 0° extension in posterior-stabilized total knee arthroplasty
Kazunori Hino,corresponding author1 Tatsuhiko Kutsuna,1 Kunihiko Watamori,1 Hiroshi Kiyomatsu,1 Yasumitsu Ishimaru,1 Jun Takeba,1 Seiji Watanabe,1 Yoshitaka Shiraishi,2 and Hiromasa Miura1Knee
Introduction
Midflexion 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 methods
Forty-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.
Results
The 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°.
Conclusions
The 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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