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.