Abstract
BACKGROUND: The anterior cruciate ligament (ACL) is integral to maintaining knee joint stability but is susceptible to rupture during physical activity. Despite surgical restoration of passive or mechanical stability, patients struggle to regain strength and prior level of function. Recent efforts have focused on understanding how ACL-related changes in the nervous system contribute to deficits in sensorimotor control following injury and reconstruction. We hypothesize that these challenges are partially due to an increase in sensorimotor uncertainty, a state that reduces the precision of movement control. OBJECTIVES: This review proposes the ACL NOISE (Neuroplastic Outcomes from Impaired Sensory Expectations) hypothesis, reframing current literature to provide a case that increased sensory noise following ACL injury and reconstruction disrupts sensory predictions, which are anticipations of immediate sensory outcomes or motor commands. This disruption in sensory predictions may contribute to altered neurophysiology, such as cross-modal brain activity, and other persistent clinical deficits. DESIGN: Narrative review RESULTS/FINDINGS: Following ACL injury and reconstruction, the knee and nervous system experience various neurophysiological alterations to overcome elevated sensory uncertainty and inaccurate sensory predictions, contributing to persistent motor deficits. CONCLUSIONS: We provide a theoretical case based on compelling evidence that suggests prolonged impairment after ACL injury may be secondary to uncertainty in knee sensory perception. Future research should consider testing the NOISE hypothesis by creating a paradigm that examines dynamic joint stability in response to unexpected perturbations. This approach would help assess motor coordination errors and drive the development of clinical strategies aimed at reducing sensory uncertainty following ACL reconstruction.