Assessing Quadriceps Strength After Anterior Cruciate Ligament Reconstruction: Reliability, Validity, and Diagnostic Accuracy of a Pull-Based Portable Dynamometer.

CONTEXT: Pull-based portable dynamometers may provide an affordable and clinically feasible alternative for objectively assessing quadriceps strength after anterior cruciate ligament reconstruction. We examined the reliability, validity, and diagnostic accuracy of a pull-based dynamometer compared with an isokinetic dynamometer when assessing quadriceps strength in young adults with a history of anterior cruciate ligament reconstruction.

DESIGN

Controlled laboratory study.

METHODS

Our sample included 25 individuals with a history of unilateral anterior cruciate ligament reconstruction >4 months prior. We performed 3 tests of bilateral quadriceps strength during a single laboratory visit with 5 minutes of rest between tests. We first tested with the isokinetic dynamometer and then performed 2 tests with the pull-based dynamometer (test and retest). For each test, we collected the average maximal knee extension torque from 3 trials on each limb and then calculated normalized unilateral quadriceps strength (Newton meter per kilogram) on each limb and limb symmetry index. We assessed intrarater reliability and validity using intraclass correlation coefficients (ICC) with 95% confidence intervals (CI) for absolute agreement (reliability and validity) and consistency (validity). We assessed diagnostic accuracy using sensitivity and specificity calculations for the pull-based dynamometer's ability to identify individuals with or without a limb symmetry index <90% compared with the isokinetic dynamometer.

RESULTS

The pull-based dynamometer demonstrated good-to-excellent test-retest reliability for all strength outcomes (ICC 95% CI = .89-.99). The pull-based dynamometer demonstrated good-to-excellent consistency (ICC 95% CI = .79-.98) with the isokinetic dynamometer for all 3 outcomes, but poor-to-excellent agreement (ICC 95% CI = .13-.96). The pull-based dynamometer identified 84% of participants with or without a limb symmetry index <90% with perfect specificity (100%) and good sensitivity (71%).

CONCLUSIONS

The pull-based dynamometer performed reliable, consistent, and diagnostically accurate quadriceps strength measures compared with the isokinetic dynamometer, but strength values were not interchangeable between devices. Pull-based portable dynamometry may provide a low-cost, alternative tool for objectively assessing quadriceps strength when an isokinetic dynamometer is unavailable.