Evaluating lower-limb asymmetry in acl-patients: assesment of jumping performance and mechanical muscle function

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Introduction: The ratio between the operated and nonoperated leg is typically used to distinguish between normal or abnormal test scores in knee patients (1). Traditionally, the asymmetry ratios are investigated by use of functional tests (i.e. one-leg jump for distance). However, mechanistic outcomes such as kinematic/kinetic data and isolated muscle force/power output may provide further insight into the origin of between-limb asymmetry. The study aim was to investigate differences in asymmetry ratios of unilateral jumpperformance bymeans of kinetic and kinematic analysis andmechanicalmuscle function in ACL-patients and healthy controls. Patients/materials and methods: This case-control study was performed in 23 ACL-reconstructed men (mean age: 27.2 ± 7.5 years and BMI: 25.4 ± 3.2) 18-30 month post-surgery and 25 healthy matched controls (mean age: 27.2 ± 5.4 years and BMI: 24.1 ± 1.8). Patients and controls performed (i) bilateral maximal counter movement jumps (CMJ) with each leg positioned on a separate force plate and (ii) maximal single-leg CMJs. Kinematic data were synchronously recorded by a 6 cameraViconMX system. Subsequently, center of mass jump height (JH), unilateral knee joint range of motion (ROM), unilateral peak (Mpeak) and mean sagittal knee moment (Mmean) were analyzed for the concentric phase, (iii) one-leg maximal jump for distance was performed [1], and (iv)maximal unilateral isometric knee extensor and flexor strength (MVC)weremeasuredusing stabilizeddynamometry [2]. Asymmetry ratios were calculated as operated/non-operated leg for ACLpatients, and non-dominant/dominant leg for controls. Good-tomoderate test-retest reliability has been reported for all measured variables [3]. Differences in asymmetry ratios were evaluated by student’s t-tests using a 0.05 level of significance. Results: No differences in age or BMI were observed between groups. CMJ:Asymmetry ratios for knee jointROMdiffered (p<0.01) between patients and controls in both types of CMJ (96.1% vs. 102.6% and 87.0% vs. 99.9% in bilateral and single-leg CMJs, respectively). Jump for distance: Patients demonstrated greater (p<0.01) asymmetry for jump length (92.9% vs. 98.6%). MVC: Asymmetry in hamstring MVC was greater (p<0.001) for patients than controls (77.4% vs. 101.3%). Discussion & conclusions: ACL patients showed reduced function of the operated leg 18-30 month post ACL-reconstruction for knee ROM, singleleg jump for distance and hamstring MVC. The most prominent reduction was observed for maximal hamstring muscle strength. This finding has significant clinical implications since the hamstring muscles are important protagonists to the ACL [4,5], with reduced hamstring MVC thus representing a potential risk factor for secondary ACL-rupture.