Hop tests predict future symptoms, function and return to sport after ACL injury: a systematic review and meta-analysis

Abstract

Introduction: Following anterior cruciate ligament (ACL) injury, functional deficits (e.g., lower-limb muscle strength/power) can persist beyond typical rehabilitation periods. Hop tests are frequently used clinical assessments that provide insight into current lower-limb function to monitor rehabilitation progress and inform readiness to return to sport. Longitudinal data also suggests that hop tests are important prognostic factors for future outcomes, such as risk of re-injury. However, no systematic review has synthesized the evidence of the prognostic capacity of hop tests on knee-related outcomes following ACL injury. Method: This review identified longitudinal studies reporting the association between hop tests and future (≥3 months later) knee-related outcomes (e.g., return to sport, symptoms, re-injury, osteoarthritis) following ACL injury. Where possible, meta-analyses were applied on the basis of the standardised mean difference (SMD) of the association between hop test performance (limb symmetry index score [ACL limb ÷ contralateral limb x 100]) and knee-related outcome. Results: Searching six databases identified twenty-nine studies. All included the hop for distance test and 11 included a repeated forward hop test (triple-crossover [n=8], triple-forward [n=2], 6m-timed hop [n=1]). Meta-analysis revealed greater limb-symmetry with the hop for distance and repeated forward hop tests (6-12 months post-ACL reconstruction) was associated with: i) higher return to sport rates 1-2 years post-operatively (SMD 0.33; 95%CI 0.01, 0.66 and 0.55; 95%CI 0.15, 0.95, respectively); and ii) better symptoms and function 2-5 years post-ACL reconstruction (SMD 0.49; 95%CI 0.23, 0.76 and 0.80; 95%CI 0.28, 1.33, respectively). Lower hop test performance may be associated with a moderate increased risk of knee osteoarthritis (SMD 0.38; 95%CI -0.31, 1.07 and 0.52; 95%CI -0.10, 1.14, respectively) but more studies are needed to be conclusive. Performance on hop tests were not associated with the ability to cope with an ACL-deficient knee or re-injury risk. Discussion: Performance on hop tests following ACL injury and reconstruction is a useful prognostic indicator of symptomatic, functional and return to sport outcomes. The results of this systematic review indicate that easy, cheap and quick hop tests can be used to identify individuals who are likely to be at higher risk of poor longer-term outcome after ACL injury and reconstruction, and to help guide rehabilitation programs. Conflict of interest statement: My co-authors and I acknowledge that we have no conflict of interest of relevance to the submission of this abstract.