Functional Brain Plasticity Associated with ACL Injury: A Scoping Review of Current Evidence

Abstract

Anterior cruciate ligament (ACL) injury is a common problem with consequences ranging from chronic joint instability to early development of osteoarthritis. Recent studies suggest that changes in brain activity (i.e., functional neuroplasticity) may be related to ACL injury. The purpose of this article is to summarize the available evidence of functional brain plasticity after an ACL injury. A scoping review was conducted following the guidelines of the Joanna Briggs Institute and the Preferred Reporting Items for Systematic Reviews and Meta-Analyses. The terms “brain,” “activity,” “neuroplasticity,” “ACL,” “injury,” and “reconstruction” were used in an electronic search of articles in PubMed, PEDro, CINAHL, and SPORTDiscus databases. Eligible studies included the following criteria: (a) population with ACL injury, (b) a measure of brain activity, and (c) a comparison to the ACL-injured limb (contralateral leg or healthy controls). The search yielded 184 articles from which 24 were included in this review. The effect size of differences in brain activity ranged from small (0.05, ACL-injured vs. noninjured limbs) to large (4.07, ACL-injured vs. healthy control). Moreover, heterogeneity was observed in the methods used to measure brain activity and in the characteristics of the participants included. In conclusion, the evidence summarized in this scoping review supports the notion of functional neuroplastic changes in people with ACL injury. The techniques used to measure brain activity and the presence of possible confounders, as identified and reported in this review, should be considered in future research to increase the level of evidence for functional neuroplasticity following ACL injury.

A Multi-Systems Approach to Human Movement after ACL Reconstruction: The Nervous System

“…15 Previous authors have aimed to better understand the cortical contributions to altered sensorimotor processing, potentially predisposing individuals to ACL injury risk 16 as well as protracted recovery following ACLR. 17,18 Research tools such as neuroimaging (functional magnetic resonance imaging [fMRI]) and transcranial magnetic stimulation (TMS) are commonly used to determine whole brain and motor cortex alterations respectively, after ACLR. Changes within the spinal cord are commonly measured using the Hoffmann Reflex (H-Reflex) which assesses the integrity of Ia afferent synaptic transmission contributing to the alpha motor neuron pool of the quadriceps within the anterior horn of the spinal cord.…”

Can We Capitalize on Central Nervous System Plasticity in Young Athletes to Inoculate Against Injury?

“…We selected a lower bound age range of ~ 6 years old indicative of the age period in which youth generally exhibit the requisite motor competence to benefit from training/resistance/agility programs, possess sufficient level of physical and emotional maturity, and/or is ready for structured sports participation [10, 91-96, 98, 99, 105, 115]. An older bound age range of ~ 25 years old was included to be cognizant of the college-aged participants that constitute the majority of studies providing empirical data for the neuroplasticity of ACL injury [122] and OPTIMAL motor learning [160], yet still within the age window that is burdened by such musculoskeletal trauma [76,164]. However, we emphasize the described age window should not be considered fixed or restricted based on chronological number in light of various growth/maturational factors [9,97,104].…”

“…The recent proliferation of research into the neuroplasticity associated with ACL injury has revealed distinct alterations within the CNS (using methods including functional magnetic resonance imaging [fMRI], transcranial magnetic stimulation, etc.) (for a review see Neto et al [122]), providing an opportunity to apply innovative techniques capable of treating both movement and CNS dysfunction simultaneously in youth, such as OPTIMAL PREP strategies. To support the subsequent neurophysiologic sections related to ACL injury, Fig.…”

“…Further, emergent data of direct CNS dysfunction related to ACL injury (specifically within the brain and spinal cord) has proliferated and generally fall into one of three categories in order of most empirical evidence: (1) CNS alterations following ACLR (2) CNS alterations that are associated with high ACL injury-risk biomechanics (e.g., aberrant frontal plane biomechanics) and (3) CNS dysfunction identified prior to future ACL injury. While a scoping review of these three topics are outside the aims of this report (see Neto et al [122] for such a review), we briefly describe each below to provide the foundation that supports the application of OPTIMAL PREP training strategies [34,36].…”

Functional Cortical Connectivity Related to Postural Control in Patients Six Weeks After Anterior Cruciate Ligament Reconstruction

“…A growing amount of evidence has begun identifying clinically meaningful neuroplastic changes in the sensorimotor system following ACL injury. Investigations utilizing transcranial magnetic stimulation, for instance, have detected enhanced motor thresholds in the ACL injured limb, whereas functional magnetic resonance imaging or electroencephalography (EEG) studies observed increased activations of the motor areas and lower activations of somatosensory areas in these patients (Neto et al, 2019). Along with altered somatosensory information from the ACL, decreased innervation to the primary sensory cortex (Valeriani et al, 1999), as well as different corticospinal and motor cortex excitability (Pietrosimone et al, 2015;Grooms et al, 2017;Lepley et al, 2020) have been observed in patients after ACL reconstruction.…”