Neural activity differences and their functional and clinical correlates after anterior cruciate ligament...

To synthesize the evidence for brain activity differences between individuals with anterior cruciate ligament reconstruction (ACLR) and uninjured controls using task-based fMRI, and for the neural correlates of functional and clinical outcomes. A systematic search was performed across PubMed, Medline, Scopus, and Google Scholar for task-based fMRI studies post-ACLR. Inclusion required a control group comparison or correlational analysis with clinical outcomes. Methodological quality, risk of bias, and certainty of evidence were independently assessed using Downs and Black, ROBINS-I, and GRADE, respectively. Eleven studies were included. Group-level brain activity differences between ACLR and controls were apparent but highly inconsistent. However, correlational analyses revealed a consistent pattern: higher activity in sensorimotor integration regions, specifically the precuneus, supplementary motor area, and secondary somatosensory cortex, was associated with better patient-reported, biomechanical, and neurocognitive outcomes. Additionally, preliminary evidence suggests that utilizing an external focus of attention during exercise increases precuneus activity, potentially reflecting a compensatory mechanism to maintain performance. The certainty of evidence for consistent group-level neural differences post-ACLR is very low. However, with low certainty, consistent relationships exist between specific brain region activity and functional outcomes. Upregulation of sensorimotor integration networks may reflect a beneficial compensatory response to altered somatosensory input, although pre-existing neural traits cannot be ruled out. While neuroplasticity after ACLR is highly individualized, rehabilitation strategies targeting these clinically-relevant neural pathways, such as attentional focus manipulation, may optimize patient recovery.