Neural activity differences and their functional and clinical correlates after anterior cruciate ligament reconstruction: A systematic review of task-based fMRI studies

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.