Brain Activation for Knee Movement Measured Days Before Second Anterior Cruciate Ligament Injury: Neuroimaging in Musculoskeletal Medicine

BackgroundAnterior cruciate ligament (ACL) injury has multifactorial causes encompassing mechanical, hormonal, exposure, and anatomical factors. Alterations in the central nervous system also play a role, but their influence after injury, recovery, and recurrent injury remain unknown. Modern neuroimaging techniques can be used to elucidate the underlying functional and structural alterations of the brain that predicate the neuromuscular control adaptations associated with ACL injury. This knowledge will further our understanding of the neural adaptations after ACL injury and rehabilitation and in relation to injury risk. In this paper, we describe the measurement of brain activation during knee extension-flexion after ACL injury and reconstruction and 26 days before a contralateral ACL injury.MethodsBrain functional magnetic resonance imaging data for an ACL-injured participant and a matched control participant were collected and contrasted.ResultsRelative to the matched control participant, the ACL-injured participant exhibited increased activation of motor-planning, sensory-processing, and visual-motor control areas. A similar activation pattern was present for the contralateral knee that sustained a subsequent injury.ConclusionsBilateral neuroplasticity after ACL injury may contribute to the risk of second injury, or aspects of neurophysiology may be predisposing factors to primary injury.

Clinical Implications

Sensory-visual-motor function and motor-learning adaptations may provide targets for rehabilitation.Key Words: neuroplasticity, functional magnetic resonance imaging, motor control

Key Points

• After anterior cruciate ligament reconstruction, rehabilitation, and return to play, neurologic differences in knee motor control may persist.
• Anterior cruciate ligament injury and recovery may induce specific changes in brain processing regarding sensory-visual-motor integration.

Individuals who experience a primary anterior cruciate ligament (ACL) injury and return to sport may have up to a 25% chance of experiencing a second ACL injury to either knee, despite surgical reconstruction and rehabilitation.^1,2 The contralateral knee may be at greater risk of injury than the involved knee,² suggesting possible postinjury bilateral neurologic alterations or the presence of bilateral factors that contributed to the initial injury.³ Researchers have reported that these postinjury neurologic differences include disrupted central nervous system afferent function,^4,5 altered efferent output,^3,6 and changes in brain activity for motor control.^7,8Few investigators have prospectively studied the neurologic changes that occur in the brain after ACL injury, reconstruction, and rehabilitation and before subsequent injury. Therefore, the purpose of this paper was to describe the brain activation for knee motor control measured after initial ACL reconstruction (ACLR) and 3 weeks before a contralateral ACL injury. We hypothesized that the ACLR participant would have greater motor-planning and sensory-area activation than a healthy matched control participant. This postinjury neuroplasticity or predisposing neurologic function may help to explain the underlying mechanisms contributing to prolonged deficits in neuromuscular control after ACL injury.⁹