Author Identifier

Colin Sylvester: http://orcid.org/0000-0003-1076-463X  

Date of Award

2026

Keywords

ACL, neuroplasticity, tDCS, corticospinal excitability, intracortical excitability

Document Type

Thesis - ECU Access Only

Publisher

Edith Cowan University

Degree Name

Master of Medical and Health Science by Research

School

School of Medical and Health Sciences

First Supervisor

Myles Murphy

Second Supervisor

Ann-Maree Vallence

Third Supervisor

Casey Whife

Fourth Supervisor

Peter D'Alessandro

Abstract

Anterior cruciate ligament (ACL) injury and surgery are devastating for athletes and result in short- and long-term issues. A major contributing issue is reduced voluntary activation of the quadriceps, which occurs due, in part, to maladaptive changes within the corticospinal and intracortical pathways of the motor descending drive. These voluntary activation changes develop post-injury and surgery and are correlated with poor functional outcomes, such as reduced quadriceps strength. Current management for ACL injuries typically involves ACL reconstruction (ACLR) in combination with 9 12 months of rehabilitation. Unfortunately, current management does not adequately address these maladaptive changes to the corticospinal and intracortical pathways. Long-term studies show persistent deficits that are correlated with reduced voluntary activation and quadriceps strength. Improving our understanding of the maladaptive changes occurring in the corticospinal and intracortical pathways, when they occur, and how to correct them will be invaluable to the athletic and sports medicine community.

In this thesis:

* I have reviewed the literature related to measures of corticospinal and intracortical excitability in the quadriceps representation in the motor cortex in the post-injury and post-operative time periods following ACL injury.

* I have performed pre- (i.e., within four weeks of surgery) and early post-operative (i.e., two weeks) assessments of measures of corticospinal and intracortical excitability in the quadriceps and hamstrings representations in the motor cortex using transcranial magnetic stimulation.

* I have performed repeat assessment of measures of corticospinal and intracortical excitability in the quadriceps and hamstrings representations in the motor cortex following six weeks (i.e., eight weeks post-operatively) of physiotherapist-led rehabilitation combined with sham- or anodal-transcranial direct current stimulation (tDCS).

The literature review demonstrated changes do occur in corticospinal and intracortical excitability post surgery. However, there is no agreement as to which measures are affected post-surgery and when these changes occur. Longer-term studies show a correlation between reduced voluntary activation and functional outcomes (i.e., quadriceps strength) to changes in intracortical inhibition.

Study One: Pre- and post-ACLR assessment of corticospinal and intracortical pathways of the quadriceps muscle

The first study was a prospective case control study of 21 participants. I examined measures of corticospinal excitability and intracortical excitability in the quadriceps and hamstrings representations in the motor cortex in the pre-surgery (i.e., within four weeks) and acute post-operative period (i.e., two weeks). This study identified there were no changes within the corticospinal excitability of the quadriceps muscle, but intracortical inhibition and facilitation were both increased post-surgery. This suggests there is increased activity within the intracortical pathways compared to the pre-surgical assessments. There was no significant change in the intracortical excitability of the hamstrings muscle at two-weeks post-surgery.

Study Two: Assessment of corticospinal and intracortical pathway responses to anodal-tDCS used in early post-ACLR rehabilitation

The second study was a triple-blinded randomised controlled proof of concept trial with 21 participants. I examined the impact of a novel treatment, anodal-tDCS, used during six-weeks of physiotherapist-led rehabilitation on the maladaptive changes in intracortical excitability identified during the first phase of the trial. I found that participants with anodal-tDCS had decreases in both intracortical inhibition and facilitation, when compared to sham-tDCS, at eight weeks post-surgery.

Contribution to the field

This thesis is the first to demonstrate changes in intracortical inhibition occur early in the post-operative period after ACL reconstruction. Previous research on long-term post-operative outcomes has shown that increased intracortical inhibition is associated with deficits in voluntary activation and quadriceps strength. Additionally, I have shown that these maladaptive changes in intracortical excitability can be influenced with a novel treatment, anodal-tDCS, combined with acute rehabilitation.

Access Note

Appendices A & C of this thesis are not available 

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Link to publisher version (DOI)

10.25958/tde8-s766