Single-Legged Hop Tests as Predictors of Self-Reported Knee Function in Nonoperatively Treated Individuals With Anterior Cruciate Ligament Injury

Abstract

Background: Previous studies have found significant predictors for functional outcome after anterior cruciate ligament (ACL) reconstruction; however, studies examining predictors for functional outcome in nonoperatively treated individuals are lacking. Hypothesis: Single-legged hop tests predict self-reported knee function (International Knee Documentation Committee [IKDC] 2000) in nonoperatively treated ACL-injured individuals 1 year after baseline testing. Study Design: Cohort study (prognosis); Level of evidence, 2. Methods: Ninety-one nonoperatively treated patients with an ACL injury were tested using 4 single-legged hop tests on average 74 ± 30 days after injury in a prospective cohort study. Eighty-one patients (89%) completed the IKDC 2000 1 year later. Patients with an IKDC 2000 score equal to or higher than the age- and gender-specific 15th percentile score from previously published data on an uninjured population were classified as having self-reported function within normal ranges. Logistic regression analyses were performed to identify predictors of self-reported knee function. The area under the curve (AUC) from receiver operating characteristic curves was used as a measure of discriminative accuracy. Optimal limb symmetry index (LSI) cutoff for the best single-legged hop test was defined as the LSI with the highest product of sensitivity and specificity. Results: Single hop for distance symmetry indexes predicted self-reported knee function at the 1-year follow-up ( P = .036). Combinations of any 2 hop tests (AUC = 0.64-0.71) did not give a higher discriminative accuracy than the single hop alone (AUC = 0.71). A cutoff of 88% (LSI) for the single hop revealed a sensitivity of 71.4% and a specificity of 71.7%. Conclusion: The single hop for distance (LSI) significantly predicted self-reported knee function after 1 year in nonoperatively treated ACL-injured patients. Combinations of 2 single-legged hop tests did not lead to higher discriminative accuracy than the single hop alone.