Quantifying Limb Symmetry After Anterior Cruciate Ligament Reconstruction: A Comparative Analysis of Isokinetic Dynamometry and Dual Force Plate Jumping

CONTEXT: Clinicians assessing limb symmetry after ACL reconstruction (ACLR) use various tools including functional tests (eg, countermovement jump [CMJ]) and isolated strength tests (eg, isometric isokinetic dynamometry). However, it is unclear how these different assessment modalities and calculation methods compare, which may have significant implications for clinical decision making when interpreting asymmetry. DESIGN: A repeated-measures, cross-sectional observational study. METHODS: Fourteen participants post-ACLR (phase 3 rehabilitation) and 25 healthy controls were assessed. Participants completed unilateral isometric knee extension testing on an isokinetic dynamometer and bilateral CMJ testing on a dual force plate system. Asymmetry was calculated using 5 different equations. RESULTS: A within-group analysis showed that participants post-ACLR had significantly different asymmetry magnitudes when comparing the CMJ and isometric tests (mean difference = 5.64%-12.45%, P < .006). Healthy controls showed no difference in asymmetry between the 2 tests (P > .617). A between-group analysis showed that the ACLR group was significantly more asymmetric than controls on both the CMJ test (mean difference = 7.95%-22.12%, P < .001) and the isometric test (mean difference = 14.02%-36.24%, P < .001). However, both testing methods exhibited adequate sensitivity (0.79) and specificity (0.99) for differentiating those with ACLR from healthy controls. CONCLUSION: Asymmetry values are highly dependent on the assessment modality (functional jump vs isolated strength). While participants post-ACLR were more asymmetric than healthy controls on both tests, the magnitude of their asymmetry differed significantly between the 2 tests. This finding indicates that asymmetry values from functional and isolated tests are not interchangeable and underscores the need for test-specific interpretation in clinical practice.