Transcranial Direct Current Stimulation to Enhance Rehabilitation in Individuals With Rotator Cuff Tendinopathy

BACKGROUND: tDCS is a safe and easy to use technique that has emerged as a promising tool to induce plasticity and to facilitate sensorimotor rehabilitation with potential application in various clinical populations. tDCS has been shown to induce changes that outlast the duration of the stimulation, by modulating neuronal membrane potential of the targeted brain region. Depending on the flow of current, tDCS can increase or decrease neuronal excitability; anodal tDCS induces membrane depolarization and enhanced excitability of cortical neurons, whereas cathodal tDCS induces membrane hyperpolarization and reduced excitability of cortical neurons. As such, tDCS has the potential to prime the plastic potential of a given brain region, making it more responsive to another intervention. For example, it has been shown that five days of anodal tDCS combined with training promotes motor skill acquisition still detectable three months later; an effect significantly superior to sham tDCS. These effects most likely are due to the augmentation of synaptic plasticity that requires the presence of brain-derived neurotrophic factor.

Coupled with sensorimotor training, tDCS can lead to subsequent sustained clinical gains.The beneficial effects of tDCS combined with sensorimotor training to normalize motor cortical activity and to enhance rehabilitation have been shown in populations with neurological injuries, such a stroke. In musculoskeletal populations, anodal tDCS over M1 has also been shown to lead to significant pain level reduction. Evidence suggests that tDCS over M1 may relieve pain through inhibition of thalamic sensory neurons and disinhibition of neurons located in the periaqueductal gray matter. In these latter studies, tDCS was specifically aimed at reducing pain and was not coupled with sensorimotor training. In fact, evidence on the effect of tDCS coupled with sensorimotor training in musculoskeletal populations is scarce, and the effect of such intervention has never been evaluated in individuals with RC tendinopathy. Considering that RC tendinopathy is associated with impaired motor control and that pain can decrease the excitability of the motor cortex and impair motor learning, the investigators believe that it is relevant to determine whether tDCS can enhance sensorimotor training, and improve outcome.

PURPOSE - The primary objective of this randomized control trial is to compare, in terms of symptoms and functional limitations, a group receiving a rehabilitation program centered on sensorimotor training combined with anodal tDCS to a group receiving the same rehabilitation program combined with sham tDCS in individuals with RC tendinopathy. A secondary objective is to explore the effects of these interventions on shoulder control and corticospinal excitability.

METHODS - Study Design: This triple-blind (patients, therapist & evaluator), parallel-group randomized control trial will include four evaluation sessions over 6 months (baseline, week 3, week 6, 3-month) and a 6-week rehabilitation program.

Interventions: Each participant will take part in the same 8-week rehabilitation program supervised by an independent physiotherapist. This program, previously shown effective, targets the deficits described in individuals with RC tendinopathy. It includes sensorimotor training, strengthening, and patient education. Each session lasts 40 minutes, with at least 75% for sensorimotor training. The rest of the session is used to teach and revise home exercises. tDCS will be applied during sensorimotor training (30 min),but only during the first five sessions, as these sessions will be during the first phase of motor learning, characterized by considerable improvement in performance.

Statistical Analyses - Descriptive statistics will be used for all outcome measures at each measurement time to summarise results. Baseline demographic data will be compared (independent t-test and Chi-squared tests) to establish the comparability of groups. All data will be tested to check the distributional assumptions for the inferential statistical analyses. An intention-to-treat analysis will be used in which all participants will be analysed in the group to which they were originally assigned. All dropouts and the reason for dropping out of the study will be reported. Any harm or unintended effects during the programs will be recorded. A 2-way ANOVA (2 tDCS [Real or Sham] x 4 Time [week 0, 3, 6, 12]) will be used to analyse the effects of tDCS on primary outcome and secondary outcomes.

Inclusion criteria

• painful arc of movement
• positive Neer or Kennedy-Hawkins tests
• pain on resisted isometric lateral rotation or abduction, or positive Jobe test. The diagnosis accuracy of the combination of these tests has been studied (sensitivity & specificity ≥ 0.74)

Exclusion criteria

• fracture at the symptomatic upper limb;
• previous neck or shoulder surgery;
• shoulder pain reproduced during active neck movement;
• shoulder capsulitis;
• clinical signs of a full thickness RC tear;
• rheumatoid, inflammatory, or neurological diseases;
• behavioural or cognitive problems.