Analysis of limb kinetic asymmetry during a drop vertical jump in adolescents post anterior cruciate ligament reconstruction

Background: Limb asymmetry after ACL reconstruction is often cited as a risk factor for ACL reinjury. We assessed ground reaction forces on each limb during a drop vertical jump, and compared kinetic symmetry between limbs in adolescents post-ACL reconstruction versus healthy controls. Methods: Forty-four participants who underwent an ACL reconstruction (16 male/28 female, mean age 16.1 +/- 1.5, mean 7.3 +/- 0.9 months post-ACL reconstruction) and 34 controls (20 male/14 female, mean age 14.9 +/- 1.1) completed a drop vertical jump captured on a Vicon system and Bertec force plates. Kinetic variables were calculated individually for each limb. Inter-limb asymmetry was calculated as an index between each limb (involved versus uninvolved for the ACL reconstruction group, and left versus right for controls), and was compared between groups using independent t-tests. Findings: Asymmetry was significantly more pronounced in the ACL reconstruction group versus the controls for peak contact ground reaction force (11.6% vs 4.4%, p = 0.009), eccentric impulse (8.8% vs 3.8%, p = 0.009), eccentric mean force (8.0% vs 3.4%, p = 0.006), concentric peak ground reaction force (4.1% vs 0.8%, p = 0.003), concentric impulse (5.1% vs 1.1%, p = 0.001), and peak landing ground reaction force (12.7% vs 1.7%, p < 0.001). Interpretation: Limb kinetic asymmetry during a drop vertical jump was more pronounced in adolescents postACL reconstruction versus controls for both eccentric- and concentric-phase variables, which may indicate the use of compensatory strategies to offload the post-operative limb. Targeted interventions to produce more symmetric loading and unloading during jumping tasks should be developed, tested, and monitored to determine the impact on rehabilitation programs, return-to-sport evaluations, and injury prevention outcomes.