Relations Between Return to Play Unilateral Knee Extension Strength and Triple-Hop Tests

Abstract

Unilateral assessments are used to monitor the restoration of strength and strength symmetry following unilateral injury, such as an anterior cruciate ligament (ACL) tear. PURPOSE: To assess the relation between unilateral isokinetic knee extension (KE) strength and triple hop distance in post-operative ACL reconstruction patients at the time of return to sport (RTS). METHODS: Thirty patients (15 male; 18 ± 6 y; 1.75 ± 0.13 m; 76 ± 19 kg) were assessed for unilateral isokinetic KE strength at 180° s-1 and triple hop distance. Peak KE strength on the involved leg (IL) and uninvolved leg (UIL) were averaged to obtain an overall strength value and strength asymmetry was calculated between legs as a percentage. Participants were stratified into four groups based on the cohort’s overall median strength and strength asymmetry values (low strength low asymmetry, low strength high asymmetry, high strength low asymmetry, and high strength high asymmetry). Pearson correlations were used to determine the relation between KE strength and triple hop distance. One-way analysis of variance was used to assess the effect of group on triple hop distance on IL and UIL. T-tests were used to determine the source of identified effects and to compare IL to UIL in each group. RESULTS: For all patients, the mean IL and UIL KE strength was 1.52 ± 0.59 Nm kg-1 and 1.68 ± 0.61 Nm kg-1, respectively, and the median KE strength asymmetry was 13.2%. The mean IL and UIL triple hop distance was 4.27 ± 1.09 m and 4.26 ± 1.27 m, respectively. No significant correlations were identified between UIL KE strength and triple hop distance (r = 0.34; p > 0.05), but were identified for IL KE strength and triple hop distance (r = 0.40; p = 0.03). No significant effect of group for IL was identified (p > 0.05) but was identified for UIL (p = 0.03), though individual comparisons were not significant (p > 0.05). Among all groups, triple hop distance was not significantly different between IL and UIL (p > 0.05). CONCLUSION: The low explained variance between KE strength and triple hop distance suggests these test shouldn’t be used in isolation during RTS testing. Groups may have demonstrated similar triple hop distance because demand may be shifted to proximal or distal joints during unilateral hopping, which masks unilateral KE strength deficits and results in symmetrical unilateral function.