Biomechanical effects of neuromuscular training in anterior cruciate ligament-reconstructed subjects

Objectives: Second anterior cruciate ligament (ACL) injuries occur at a 10-20-fold higher rate than primary injury, and result in significantly poorer outcomes. Targeted neuromuscular training (NMT) alters biomechanics and reduces rates of primary ACL injury, but its effects in an ACL-injured population have not been elucidated. The purpose of this study was to determine the effects of NMT on high-risk biomechanics at the hip and knee in ACL-reconstructed (ACLR) subjects. We hypothesized that trained subjects would demonstrate reduced peak hip rotation and knee abduction motion and moments compared to controls. Methods: 13 ACLR subjects (7 males and 6 females, 20.15±7.97 years old) were enrolled and evaluated during drop vertical jump (DVJ), single leg drop (SLD), and crossover drop (COD) tasks using 3D motion analysis prior to and after participation in a 12 session NMT program (Pre: 36.0±18.3 weeks post-operative, Post: 46.6±17.4 weeks post-operative). 13 untrained, ACLR controls (9 males and 4 females, 20.77±6.55 years old) were tested 52.4±2.7 weeks post-operative. Trained subjects participated in a 12 session training program, modified to be safe for patients in the late recovery phase after ACL-injury. The protocol centered around seven separate progressions, each consisting of four phases of increasing difficulty. Each phase consists of a cognitive session, associative session, and autonomous session.1 Discrete variables for hip and knee kinematics and kinetics, and vertical ground reaction force were compared within and between groups. Limb-by-session repeated measures analysis of variance (ANOVA) was used to assess withinsubject effects of training. A separate limb-by-group ANOVA was used to compare trained and untrained groups. Results: Frontal plane hip excursion during the COD decreased after training. Trained subjects demonstrated increased knee flexion at initial contact during the DVJ task after training (NMT_Pre: - 17.1±6.7 degrees, NMT_Post: -22.5±10.2 degrees; p=0.02). Changes in knee kinematics from pre-to post- NMT are shown in Figure 1. Peak knee flexion within the first 20% of landing increased significantly after NMT (NMT_Pre: -69.2±8.8 degrees, NMT_Post: -74.8±9.2 degrees; p=0.0067) as well as throughout the task (NMT_Pre: -88.2±12.1 degrees, NMT_Post: -95.0±12.5 degrees; p=0.0095). Trained subjects demonstrated significantly greater knee flexion range of motion within the first 20% of the landing phase of DVJ compared to controls (NMT_Post: 52.3±12.8 degrees, CTRL: 45.6±7.7 degrees; p=0.0214). Trained groups demonstrated greater peak knee flexion and flexion ROM compared to controls (p<0.05). Peak hip flexion during the first 20% of DVJ increased from pre- to post-training, but only trended toward differing from controls (p=0.0879). Conclusion: Increased knee flexion angles for both unilateral and bilateral tasks were consistently observed from pre- to post-training. Furthermore, the trained group exhibited significantly greater peak flexion compared to controls during the initial landing phase for most tasks, when ACL injury is most likely to occur. NMT in ACL-reconstructed subjects appeared to primarily affect sagittal plane hip and knee biomechanics.