Lower extremity electromyographic characteristics of patients with noncontact complete anterior cruciate ligament rupture not reconstructed in one-legged jump landings: a case-control study

There have been many studies on neuromuscular adaptation after anterior cruciate ligament (ACL) reconstruction, while the understanding of muscle activation patterns in unreconstructed patients with ACL rupture is still limited. The aim of this study was to investigate the lower limb electromyographic characteristics of unreconstructed patients with complete ACL rupture in a single-legged hopping landing task in order to deepen the understanding of motor control strategies in the ACL-deficient state and to provide a reference for rehabilitation assessment and intervention. Forty-two subjects were recruited for this study using a case-control design, with an ACL injury group (n = 21) of patients with unilateral non-contact complete rupture without reconstruction and a control group (n = 21) of healthy individuals matched for gender, dominant leg, and level of exercise. All subjects completed a single-leg hop landing task and synchronized Noraxon Ultium surface EMG signals with Bertec force plate data via the QUALISYS 3D motion capture system. EMG data were recorded from the lateral femoral (VL), medial femoral (VM), biceps femoris (BF), semitendinosus (ST), and gluteus maximus (Gmax) muscles before and after the landing for 100 ms each. Calculated metrics included activation onset time (onset-IC), peak appearance time (peak-IC), activation duration, and standardized root mean square (RMS) values. Data were analyzed by two-way ANOVA or nonparametric Scheirer-Ray-Hare test, and the significance level was set at P < 0.05. BF (P = 0.0409) and Gmax (P = 0.0469) sustained activation of the dominant leg in the injury group was significantly longer than that of the dominant leg in the control group. The onset-IC of BF (P = 0.0457), ST (P = 0.0277), and Gmax (P = 0.0192) of the dominant leg in the injury group was significantly earlier than that of the dominant leg in the control group. The peak-IC of BF (P = 0.0457) and ST (P = 0.0280) of the dominant leg in the injury group was significantly later than that of the dominant leg in the control group. The peak RMS of VL (P = 0.0171), VM (P = 0.0054), and Gmax (P = 0.0003) in the dominant leg of the injury group was significantly lower than that of the dominant leg of the control group in 100 ms after IC. Unreconstructed patients, averaging 18 months after ACL injury, continued to maintain a similar muscle pre-activation sequence as healthy individuals during the jump landing task, but showed a prolonged activation duration and reduced activation intensity, suggesting that neuromuscular activity was adjusted to maintain the kinematic profile. The delay in the peak of the posterior muscle groups (especially BF and ST) may be used to synergize tibial rearward movement and reduce forward movement and internal rotation, thus constituting a compensatory protective mechanism. The results of this study provide evidence for neuromuscular adaptation in the ACL-deficient state and are informative for preoperative functional assessment and rehabilitation intervention strategies.