This randomized controlled trial aimed to compare the short-term effectiveness of high-intensity laser therapy (HILT) and a multimodal physiotherapy program in patients with subacromial impingement syndrome (SIS). Ninety-four participants were allocated to either HILT or combined physiotherapy, and both groups received an identical supervised exercise program. Primary outcome measures included shoulder pain assessed using the visual analogue scale (VAS). Secondary outcomes included shoulder function, disability, and quality of life. Outcomes were evaluated at baseline, post-treatment, and short-term follow-up.

Subacromial impingement syndrome (SIS) is one of the most common causes of shoulder pain and functional limitation. Conservative treatment strategies, particularly exercise-based rehabilitation, are recommended as first-line therapy. High-intensity laser therapy (HILT) has recently gained attention because of its potential analgesic and anti-inflammatory effects; however, its comparative effectiveness against multimodal physiotherapy remains unclear.

This single-centre, assessor-blinded randomized controlled trial was conducted at the Department of Physical Medicine and Rehabilitation, Inonu University Hospital, Malatya, Türkiye. Adults aged 18-65 years with clinically and radiologically confirmed SIS were enrolled. Participants were allocated to either a high-intensity laser therapy group or a combined conventional physiotherapy group. Both groups additionally participated in an identical supervised exercise program.

The HILT group received class IV Nd:YAG laser therapy (1064 nm), whereas the control group received hot pack therapy, transcutaneous electrical nerve stimulation, and therapeutic ultrasound. Treatment duration was three weeks.

The primary outcome measure was pain intensity assessed using the visual analogue scale (VAS). Secondary outcomes included the Constant-Murley Score, Shoulder Pain and Disability Index (SPADI), and Short Form-36 quality-of-life assessment. Outcomes were evaluated at baseline, post-treatment, and short-term follow-up.

The study was approved by the Inonu University Clinical Research Ethics Committee (Approval No: 2015/123). The trial was retrospectively submitted for registration at ClinicalTrials.gov.

Inclusion Criteria:Inclusion Criteria:

• Adults aged 18 to 65 years
• Clinically and radiologically confirmed subacromial impingement syndrome
• Shoulder pain lasting at least 1 month and less than 6 months
• At least one positive impingement test (Neer, Hawkins-Kennedy, painful arc, or Jobe test)
• MRI findings consistent with stage I-II rotator cuff changes

Exclusion Criteria:

• Previous shoulder surgery or trauma
• Inflammatory rheumatic disease
• Recent myocardial infarction
• Active infection
• Previous physiotherapy or corticosteroid injection within the last 6 months
• Pregnancy
• Calcific tendinitis
• Adhesive capsulitis
• Cervical radiculopathy
• Neurological disorders affecting the shoulder
• Full-thickness rotator cuff tear
• Contraindications to electrotherapy or laser therapy

Exclusion Criteria:

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Outcome assessment was performed by a physician blinded to group allocation. Due to the nature of the interventions, participant and care provider blinding were not feasible.