Quantitative assessment of rotatory instability after anterior cruciate ligament reconstruction

Background: Anterior cruciate ligament reconstruction successfully reduces anterior knee instability, but its effect on rotatory stability is not fully understood. In addition, a definitive method for the quantitative evaluation of rotatory instability remains to be established. Hypothesis: Measurement of anterolateral tibial translation by open magnetic resonance imaging could positively correlate with the clinical grading of the pivot-shift test and would clarify residual rotatory abnormalities not shown by conventional methods for measurement of anterior stability. Study Design: Controlled laboratory study. Methods: An anterior cruciate ligament-reconstructed group (n = 21) and an anterior cruciate ligament-deficient group (n = 20) were examined using a Slocum anterolateral rotatory instability test in open magnetic resonance imaging. Anterior tibial translation was measured at the medial and lateral compartments by evaluating sagittal images. Clinical knee stability was evaluated before the above measurement using the pivot-shift test, KT-2000 arthrometer, and stress radiography. A cutoff value for anterolateral tibial translation relating to pivot-shift was determined using a receiver operating characteristic curve. Results: Side-to-side differences of anterolateral tibial translation correlated with clinical grade of the pivot-shift test and stress radiography but not with KT-2000 arthrometry in both groups. The cutoff value was established as 3.0 mm. Although the mean anterolateral translation showed no difference, 9 reconstructed knees revealed greater than 3 mm of anterolateral tibial translation, whereas only 3 uninjured knees did. Conclusion: Measurement using an open magnetic resonance imaging successfully quantified the remaining rotatory instability in anterior cruciate ligament-reconstructed knees. Clinical Relevance: This method is a useful means for quantifying anterior cruciate ligament function to stabilize tibial rotation.