The Association Between Knee Confidence and Muscle Power, Hop Performance, and Postural Orientation in People With Anterior Cruciate Ligament Injury

STUDY DESIGN: Cross-sectional. BACKGROUND: The association between muscle function and lack of knee confidence in people with anterior cruciate ligament (ACL) injury has not been well investigated. Such knowledge would help in the design of training programs for this population. OBJECTIVE: To investigate associations between self-reported knee confidence and muscle function in patients with ACL injury. METHODS: Cross-sectional data from 54 patients (mean age, 30 years; range, 20-39 years; 28% women) with ACL injury, treated with training and reconstructive surgery (n = 36) or training only (n = 18), were assessed 3 +/- 1 years after injury. Univariate and multivariable ordinal regression analyses were conducted to test the association between the patient's knee confidence (question 3 from the Knee injury and Osteoarthritis Outcome Score as the dependent variable) and performance on tests of muscle power, hop performance, and postural orientation (test for substitution patterns score) as independent variables (absolute value on the injured leg, and limb symmetry index [LSI; injured leg/uninjured leg x 100] or absolute difference between the injured and uninjured legs). RESULTS: Sixteen patients reported no trouble with lack of knee confidence, 24 mild trouble, 10 moderate trouble, and 4 severe or extreme trouble. Univariate analyses revealed significant associations between worse knee confidence and lower (worse) LSIs for knee extension power, vertical jump, and side hop, and worse test for substitution patterns scores. In the multivariable analysis, worse vertical jump LSI (P =.043) and worse side hop LSI (P =.012) significantly accounted for 25% of the variation in perceived knee confidence. CONCLUSION: Between-leg differences during demanding tasks are associated with knee confidence in individuals with ACL injury.