Abstract

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.

Highlights

  • 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° extension and 90° flexion and that at the midflexion range

  • Values dividing the amount of varus–valgus stability at 90° by the amount of varus–valgus stability at 0° were significantly correlated with the amount of varus–valgus stability at 10° and 50°–80° (Table 2)

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Summary

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. Conclusions The present study confirmed the importance of acquiring stability at 90° flexion to achieve midflexion stability in PS-TKA. Attention to soft tissue balancing is necessary to stabilize a knee at the initial flexion range in PS-TKA. Studies on midflexion stability have been limited due to the difficulty of correctly assessing the knee flexion angle, despite its importance. Insufficient assessment of the midflexion stability may have resulted in apparently contradictory conclusions about the association between stability and outcomes in previous studies.

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