In vivo measurement of the pivot-shift test in the anterior Cruciate ligament-deficient knee using an electromagnetic device

Background: The pivot-shift test is commonly used for assessing dynamic instability in anterior cruciate ligament-insufficient knees, which is related to subjective knee function, unlike static load-displacement measurement. Conventional measurements of 3-dimensional position displacement cannot assess such dynamic instability in vivo and produce comparable parameters. Not only 3-dimensional position displacement but also its 3-dimensional acceleration should be measured for quantitative evaluation of the pivot-shift test. Hypothesis: Knees with a positive pivot-shift test result have increased tibial anterior translation and acceleration of its subsequent posterior translation, and they are correlated with clinical grading. Study Design: Controlled laboratory study. Materials and Methods: Thirty patients with isolated anterior cruciate ligament injury were included. Pivot-shift tests were evaluated under anesthesia manually and experimentally using an electromagnetic knee 6 degrees of freedom measurement system. From 60 Hz of 6 degrees of freedom data, coupled tibial anterior translation was calculated, and acceleration of posterior translation was computed by secondary derivative. Results: All anterior cruciate ligament-deficient knees demonstrated a positive pivot-shift test result. The coupled tibial anterior translation was 7.7 and 15.6 mm in anterior cruciate ligament-intact and -deficient knees, respectively. The acceleration of posterior translation was -797 and -2001 mm/s(2), respectively. These differences were significant (P < .01). The coupled tibial anterior translation and acceleration of posterior translation in the anterior cruciate ligament-deficient knee were larger in correlation with clinical grading (P = .03 and P < .01, respectively). Conclusion: The increase of tibial anterior translation and acceleration of subsequent posterior translation could be detected in knees with a positive pivot-shift result, and this increase was correlated to clinical grading. Clinical Relevance: These measurements can be used for quantified evaluation of dynamic instability demonstrated by the pivot-shift test.