Transcranial Electrical Stimulation in Subacromial Pain Syndrome

The goal of this clinical trial is to analyze whether a physiotherapy protocol based on strengthening exercises to the shoulder girdle muscles carried on during anodal transcranial electrical stimulation (a-TES) is more effective on the symptoms and functionality of subjects with subacromial pain syndrome than an isolated strengthening program.

The main questions it aims to answer are:

* Is the strengthening + a-TES protocol effective on functionality?
* Is the strengthening + a-TES protocol effective on quality of life?
* Is the strengthening + a-TES protocol effective on pain?
* Is the strengthening + a-TES protocol effective on muscle strength?
* Is the strengthening + a-TES protocol effective on active range of movement?
* Is the strengthening + a-TES protocol effective on proprioception?
* Is the strengthening + a-TES protocol effective on posture?
* Is the strengthening + a-TES protocol effective on glenohumeral and scapulothoracic kinematics?

Participants will perform an 8 weeks-3 days/week shoulder strengthening protocol for the rotator cuff and scapulothoracic muscles using elastic bands and dumbbells. The rotator cuff exercises will be performed while they receive a-TES using a neoprene helmet with the electrodes placed in the opposite hemisphere to the affected side. The scapulothoracic exercises will be performed without the transcranial stimulation.

The experimental group will receive real a-TES, and will be compared with a control group that will perform the same therapeutic exercises but with placebo a-TES to see the effectiveness of the a-TES on the outcomes cited above.

The project has obtained the approval of the Ethics Committee of the University of Valencia on June 6, 2023 (Id: UV-INV_ETICA-2701990).

The intervention will take place in the laboratories of the Physiotherapy Department of the University of Valencia. All the participants, once they have signed the informed consent and, after being randomly assigned to the EG or the CG, will be evaluated before starting the treatment (T0). A post-intervention evaluation will be carried one day after the end of the 24 sessions (T1), and a follow-up evaluation 3 weeks after the intervention (T2).

Subjects with unilateral shoulder pain will be recruited through social media and posters posted in primary care centers, hospitals, and other related locations.

The study will be triple blind: participants, evaluators and therapists. In order to monitor the possible adverse effects derived from the application of a-TES, the Bruitoni et al. Adverse Effects Questionnaire will be completed in each session. It is a questionnaire that contains 10 possible side effects (headache, neck pain, scalp pain, tingling, itching, burning, redness of the skin, drowsiness, concentration problems, severe mood change).If any of these symptoms occurred, the stimulation would be stopped and the next day would be tried again. If these effects were repeated, especially the headache or were of severe intensity, the patient would be withdrawn from the investigation.

The sample size has been calculated with the formula: n = (2 \* (Zα/2 + Zβ) / d) ² (significance level of 0.05, Zα/2 = 1.96; Zβ =0.84, d= 0.5). Total, n= 64 subjects. In addition, the sample may be increased by 15% in anticipation of possible losses throughout the study (= 10 more subjects). Classic statistical methods will be used to calculate the mean as a measure of central tendency and the standard deviation as a measure of dispersion. Before carrying out the inferential analysis, the normal distribution of the sample will be checked using the Shapiro-Wilk test, homoscedasticity using the Levene test, and sphericity using the Mauchly test. Regarding the inferential analysis, a mixed ANOVA will be used with an intra-subject factor (time), with 4 categories, corresponding to the assessments made; and a between-subjects (group) factor corresponding to the assigned intervention. For post hoc comparisons, the Bonferroni adjustment will be used. In the event that the assumptions are not met, the corresponding non-parametric tests will be applied: Wilcoxon and Mann Whitney, adjusting the type I error. In the event of losses, the intention-to-treat procedure will be used for the statistical analysis of the data. .

Eligibility Criteria:
Subjects will be evaluated during a first consultation by a physiotherapist with experience in shoulder musculoskeletal pathology, following the algorithm for the diagnosis of shoulder problems, recommended by the British Elbow \& Shoulder Society with the aim of detecting possible "flags red" and as a guide to rule out other shoulder pathologies that do not fit into the SDS. However, other tests will be added to ensure diagnostic accuracy, and these are described below.

Inclusion Criteria:

1. Age between 18 and 65 years.
2. Duration of pain greater than or equal to 3 months.
3. Presence of 3 or more of the following positive clinical tests:

   * painful arc
   * External rotation test against isometric resistance
   * Neer's test
   * Jobe test or empty can test
   * Hawkins-Kennedy test

Exclusion Criteria:

1. Previous shoulder or neck surgery.
2. History of shoulder fracture or dislocation.
3. Medical diagnosis of shoulder osteoarthritis.
4. Adhesive capsulitis
5. Cervicobrachialgia or reproducible shoulder pain with neck movements.
6. Clinical signs of total tear of the rotator cuff.
7. Corticosteroid injection in the previous 6 weeks.
8. Inflammatory disease, autoimmune or rheumatic, systemic (arthritis, lupus, myopathies).
9. Cognitive or behavioral problems that make it impossible to understand and follow the intervention (score less than 24 on the Mini-Mental State Examination Score) (73).
10. Any neurological or neoplastic disease.
11. Also those who present contraindications for transcranial electrical stimulation. For this, the recommendations of the checklist of Thair et al. which includes:

    * personal and family history of epilepsy
    * metal implants in the head
    * implanted medication pump
    * pacemaker
    * recurring headaches
    * skin diseases of the scalp (psoriasis, eczema)
    * head injuries
    * serious head surgeries
    * pregnancy
    * heart diseases
    * medications (psychotropics or antihistamines).