A complex motor task is required to identify neuroplastic changes in motor control of the lower extremity in Anterior Cruciate Ligament Reconstruction patients: a fNIRS study

Ke Liu¹Qin "Arthur" Zhu²Weidong Xu^3*

• ¹Shanghai University of Sport, Shanghai, Shanghai Municipality, China
• ²University of Wyoming, Laramie, Wyoming, United States
• ³Changhai Hospital, Second Military Medical University, Shanghai, Beijing Municipality, China

Introduction: Neuromuscular control is a crucial component in restoring dynamic joint stability following anterior cruciate ligament reconstruction (ACLR). The central nervous system, as the primary control center, has been known to exhibit neuroplastic changes. However, the motor tasks used to assess brain function of ACLR are often limited to simple and static movements. The current study aimed to compare the brain activation between ACLR patients (ACLR group) and healthy controls (CONT group) during both simple and complex motor tasks, and examined the relationship between brain activity and clinical functions to explore the underlying mechanisms of neuroplasticity.Methods: Thirty-five ACLR patients and twenty-five healthy controls participated in this study. Functional near-infrared spectroscopy was used to capture real-time brain activation during knee flexion-extension (K-FE) and single leg squat (SLS) tasks.Clinical assessments included quadriceps strength, single leg hop and self-reported functional outcomes. A two-way mixed design ANOVA was conducted with one between-subjects factor (group) and one within-subjects factor (task). The dependent variable was the change in oxyhemoglobin concentration across six brain regions.Results: For the affected limb tasks, the Primary Somatosensory Cortex (S1) and Supramarginal gyrus (SMG) showed the significant main group effects , while all brain regions showed significant main effects of task difficulty. A significant interaction between group and task was found in the SMG (P = 0.036). For the contralateral limb tasks, no significant main effect of group and task were found across all brain regions. Pre-Motor Cortex (PMC), S1, Frontal Eye Fields (FEF) and SMG showed significant interaction effects between group and task (PPMC = 0.013, PS1 = 0.015, PFEF=0.015, PSMG=0.018). Multiple negative correlations were found between increased ΔHbO and functional outcomes in various brain regions depending on the limb and task.Conclusion: Brain activation increased with task difficulty. ACLR patients showed lower somatosensory cortex activation during affected limb tasks. Their task-adaptation was weaker than that of healthy controls, suggesting deficits of proprioception and lack of neural resources for adaptation to task complexity. Significant interaction effects observed during contralateral limb tasks indicated a compensatory role of the contralateral limb. These conclusion were supported by correlations with clinical outcomes.