Effects of Transcranial Neuromodulation on Rehabilitation Outcomes After Anterior Cruciate Ligament Injury: A Systematic Review of Randomized Controlled Trials

<b>Background/Objectives</b>: Anterior cruciate ligament (ACL) injuries frequently lead to long-term quadriceps impairments despite surgical repair. There is growing evidence that these deficits are caused in part by alterations in the central nervous system. Thus, transcranial neuromodulation (TNM) could be valuable in ACL rehabilitation. To systematically review randomized controlled trials (RCTs) assessing the effects of TNM on neurophysiological, functional, and safety outcomes in patients with ACL injury or reconstruction. <b>Methods</b>: We conducted searches on PubMed, Scopus, Web of Science, and Cochrane. We considered all original studies evaluating TNM, including transcranial current stimulation (tCS) and transcranial magnetic stimulation (TMS), in patients with ACL reconstruction or injury. Measures of corticospinal excitability, safety, balance, and muscle strength were assessed. We employed the Cochrane RoB 2 method to assess the risk of bias. <b>Results:</b> Seven studies comprising 129 participants (64 TNM, 65 controls) were included. Most studies applied transcranial direct current stimulation (tDCS) over the primary motor cortex contralateral to the ACL injury in conjunction with physical rehabilitation. Single-session protocols demonstrated minimal effects, whereas repeated sessions resulted in improvements in corticospinal excitability, quadriceps strength, and balance. No serious adverse events were reported; minor effects included transient headache or scalp tingling. The risk of bias was assessed as low to moderate across the studies. <b>Conclusions</b>: TNM appears to be safe and may enhance functional recovery in individuals with ACL injuries when administered in multiple sessions alongside standard rehabilitation. Further high-quality trials are necessary to determine optimal protocols and long-term outcomes.