Effects of Percutaneous Electrical Stimulation in Patients With Chronic Supraspinatus Tendinopathy

Four study groups will be established, constituting the arms of the clinical trial.

Intervention Group 1 (EP + PENS + TE)

This group will consist of individuals with chronic supraspinatus tendinopathy who will receive a treatment consisting of four sessions of percutaneous electrical stimulation (one session per week) using a dual approach: applied to the supraspinatus tendon (using the electrical EP modality-percutaneous electrolysis) and to the axillary and suprascapular nerves (using the electrical PENS modality), together with a therapeutic exercise (TE) program aimed at strengthening the shoulder joint complex.

For the localization of the target structures in the affected shoulder-the supraspinatus tendon and the axillary and suprascapular nerves-a Logiq E R8 ultrasound device (General Electric®) with an L4-12T-RS transducer will be used.

The electrical stimulation program (EP and PENS) will be applied once per week for four weeks. The exercise program will be carried out for 12 weeks at home, with a supervised process of instruction and guidance regarding both the exercises and the prescribed dosage. To ensure treatment safety, particularly in the case of percutaneous electrical stimulation, a protocol for reporting and monitoring adverse effects will be implemented and maintained until 30 days after the last intervention.

EP will be performed using the EPTE® Bipolar system under ultrasound guidance, with the probe positioned longitudinally over the supraspinatus tendon. A needle (negative electrode) from Agupunt® (Barcelona, Spain), measuring 0.30 × 40 mm, will be inserted percutaneously at an approximate angle of 45° relative to the patient's surface. A 5 × 5 cm adhesive electrode (positive electrode) will be placed along the tendon-muscle pathway to close the electrical circuit. A continuous current of 350 µA intensity will be applied for 80 s, with three electrical charge deposits in different trajectories within the structurally affected area of the supraspinatus tendon. This microcurrent-level intensity produces a minimal electrical sensation that is barely perceptible and not associated with pain.

The patient will be placed in the supine position, with the upper limb in internal rotation and the hand positioned between the ipsilateral gluteus and the treatment table. If the patient is unable to maintain this position due to the pathology itself, the upper limb will be placed in the most tolerable position of shoulder internal rotation.

PENS will be applied immediately afterwards using the EPTE® Bipolar system under ultrasound guidance. For identification of the axillary nerve, the ultrasound probe will be placed longitudinally along the humerus over the middle-posterior deltoid muscle. For identification of the suprascapular nerve, the probe will be placed longitudinally over the supraspinatus muscle in order to visualize, from superficial to deep, the trapezius muscle, the supraspinatus muscle, and the suprascapular nerve within the supraspinous fossa. The patient will be placed in the prone position with the shoulders at 90° of abduction and the elbows flexed.

In both cases, an Agupunt® needle (Barcelona, Spain) measuring 0.30 × 60 mm will be inserted percutaneously at an approximate angle of 45°-55° relative to the patient's surface and positioned as close as possible to the nerve. In this case, since a symmetrical biphasic current without polar charge is used, each electrode will be connected to a needle to close the circuit.

To confirm the correct placement of the needle, each nerve will be stimulated using a pointer with several electrical pulses at a frequency of 5 Hz. Needle placement will be considered adequate if electrical stimulation with the pointer produces a visible muscle contraction in the innervated muscles. Subsequently, the circuit will be connected and a symmetrical biphasic rectangular current will be applied at a frequency of 12 Hz for 16 minutes, with an intensity adjusted to produce the strongest possible muscle contraction without causing pain.

The 12-week home-based exercise program aims to restore pain-free mobility and improve shoulder stability through exercises designed to strengthen the rotator cuff and scapular muscles. It consists of three phases and a total of 16 exercises, which will be progressively combined to complete the training sequence. The exercises for each phase will be provided to participants in written and audiovisual formats. Patients will perform three sessions per week. Exercise adherence will be recorded using an exercise diary.

This program was designed following two systematic reviews of clinical trials conducted by our research group, with several objectives: to categorize the types of exercises used in therapeutic programs, with a particular focus on those performed with elastic bands; and to evaluate the effects of home-based exercise programs compared with supervised exercise in patients with chronic rotator cuff tendinopathy.

Several in-person instruction, learning, and supervision sessions will be conducted throughout the intervention period, coinciding with the electrical stimulation sessions. With the assistance of the physiotherapist and audiovisual materials, each patient will learn the exercises and the methodology, practice them, and resolve any questions that may arise.

To facilitate adherence and performance of the program at home, participants will receive a list of exercises with a QR code linking to a video demonstrating the exercises to be performed in each phase. In this way, the patient will only need to play the video and imitate the exercises according to the prescribed regimen. In addition, they will receive an information sheet describing the progression across phases and the technical details: (i) maximum pain level during exercise and during the following 24 hours ≤ 5/10; and (ii) perceived exertion level associated with exercise repetitions equal to 7/10 on a numerical scale.

According to this latter condition, a mixed repetition model will be used, in which participants will perform a single set of up to 15 repetitions, always maintaining a value of 7/10 according to the Rating of Perceived Effort (RPE) scale. These thresholds do not directly correspond to percentages of one-repetition maximum (1RM), but they have been considered valid for prescribing therapeutic exercise in patients with pain. Load will be adjusted according to the reference indicated by modifying the tension and resistance of the elastic band. In any case, if the patient reports a higher perceived exertion or pain level, the load will be adjusted to maintain the values within the indicated range.

Intervention Group 2 (EP + placebo PENS + TE)

Patients assigned to this group will receive four EP sessions under the same conditions described in the previous group, together with four placebo PENS sessions. Likewise, the electrical stimulation program (EP and placebo PENS) will be applied once per week. The exercise program will also be carried out for 12 weeks (three sessions per week) and will include the same guidance and learning process described in the previous group.

In the case of placebo PENS, the patient position and procedure will be identical to those described in Group 1, although without the application of electrical current. The needle will be connected to the stimulation device with the same treatment duration but without intensity adjustment, so that the device light and the acoustic signal at the end of treatment will occur in the same way. This placebo method has been used in other studies with simulated percutaneous stimulation.

Intervention Group 3 (placebo EP + PENS + TE)

Patients assigned to this group will receive four placebo EP sessions and four PENS sessions under the conditions described in the previous group. Similarly, the electrical stimulation program (placebo EP and PENS) will be applied once per week. The exercise program will also be performed for 12 weeks (three sessions per week) and will include the same guidance and learning process described in the previous group.

In the case of placebo EP, the patient position and procedure will be identical to those described in Group 1, although without the application of electrical current. The needle will be connected to the stimulation device with the same treatment duration but without intensity adjustment, so that the device light and the acoustic signal at the end of treatment will occur in the same way. This placebo method has been used in other studies with simulated percutaneous stimulation.

Control Group (placebo EP + placebo PENS + TE)

Patients assigned to this group will receive four placebo EP sessions and four placebo PENS sessions under the same conditions described in Experimental Group 1. Likewise, the placebo electrical stimulation program will be applied once per week. The exercise program will also be performed at home for 12 weeks (three sessions per week) and will include the same guidance and learning process described in the previous group.

In the case of placebo EP and placebo PENS, the patient position and procedure will also be identical, but without the application of electrical current. The needles will be connected to the stimulation device for the same treatment duration but without intensity adjustment, so that the device light and the acoustic signal at the end of treatment will occur in the same way.

• Overall Perception of Clinical Change [Срок оценки: - Baseline (T0) - 4 initial weeks - (T1) - 12 initial weeks - (T2) - 24 initial weeks - (T3)]
• Kinesiophobia [Срок оценки: - Baseline (T0) - 4 initial weeks - (T1) - 12 initial weeks - (T2) - 24 initial weeks - (T3)]
• Perceived self-efficacy with pain [Срок оценки: - Baseline (T0) - 4 initial weeks - (T1) - 12 initial weeks - (T2) - 24 initial weeks - (T3)]
• Adherence to the exercise program [Срок оценки: - Baseline (T0) - 4 initial weeks - (T1) - 12 initial weeks - (T2) - 24 initial weeks - (T3)]