This prospective, randomized, double-blind controlled clinical trial aims to compare the clinical and ultrasonographic outcomes of intralesional and perilesional 5% dextrose injection in patients with partial rotator cuff tears. Eligible participants will be randomized into two parallel groups. Both groups will receive ultrasound-guided 5% dextrose injection to the supraspinatus enthesis. In addition, one group will receive intralesional 5% dextrose injection, while the other group will receive perilesional 5% dextrose injection using the peppering technique. Injections will be performed in three treatment sessions at 21-day intervals. All participants will receive a home-based exercise program after completion of the injection treatments. Clinical outcomes will be assessed at baseline, 9 weeks, and 12 weeks after treatment, and ultrasonographic outcomes will be assessed at baseline and 12 weeks.

Rotator cuff tears are one of the leading causes of shoulder pain and functional limitation. Partial rotator cuff tears may become chronic and may not respond adequately to conventional conservative treatments such as activity modification, physical therapy, and nonsteroidal anti-inflammatory drugs.

Dextrose injection is a regenerative injection therapy that aims to stimulate tissue healing responses in chronic musculoskeletal disorders. It is thought to promote fibroblast activation, collagen synthesis, and proliferative healing processes in degenerative tendon, ligament, and enthesis lesions. Ultrasound guidance allows accurate and safe delivery of the injectate to the target tissue and enables objective follow-up of tendon morphology during the treatment process.

This study will include adult patients with partial rotator cuff tears diagnosed by clinical examination and imaging. Participants will be randomized into two groups using a computer-based random number system. The researcher performing the randomization will know the treatment allocation, while the participants and the physician assessing the clinical outcomes will be blinded to treatment groups.

Both groups will receive ultrasound-guided 5% dextrose injection to the supraspinatus enthesis. The intralesional group will additionally receive intralesional 5% dextrose injection, and the perilesional group will additionally receive perilesional 5% dextrose injection. Injections will be applied using the peppering technique, with 0.1-0.2 cc administered to each point. A total of three treatment sessions will be performed at 21-day intervals.

Clinical outcomes will include shoulder pain assessed by the Numeric Rating Scale, shoulder pain and disability assessed by the Shoulder Pain and Disability Index, and health-related quality of life assessed by the Short Form-12 Health Survey. Ultrasonographic outcomes will include supraspinatus tendon thickness and partial defect size. Clinical evaluations will be performed at baseline, 9 weeks, and 12 weeks after treatment. Ultrasonographic evaluations will be performed at baseline and 12 weeks.

Inclusion Criteria:

• Diagnosis of partial rotator cuff tear by a specialist physician after appropriate clinical examination and imaging evaluation
• Shoulder pain and functional limitation lasting for at least 3 months
• Clinically confirmed shoulder impingement findings, defined as at least one positive test among Neer, Hawkins-Kennedy, or painful arc tests
• Age between 18 and 75 years
• Ability to comply with the study procedures and attend follow-up visits regularly
• Willingness to participate in the study and provide written informed consent

Exclusion Criteria:

• Advanced cognitive impairment or dementia preventing reliable completion of questionnaires
• Refusal to participate in the study or inability to provide informed consent
• Full-thickness rotator cuff tear
• Major tendon pathology other than the supraspinatus tendon, such as full-thickness subscapularis tear or biceps tendon rupture
• Advanced acromioclavicular joint osteoarthritis, marked impingement, or marked adhesive capsulitis
• Advanced glenohumeral joint arthritis
• Active infection, cellulitis, or dermatologic lesion at the injection site
• Bleeding diathesis or anticoagulant use
• Known allergy or intolerance to dextrose injection
• Intra-articular shoulder injection, including steroid, platelet-rich plasma, or prolotherapy, within the last 3 months
• Previous shoulder surgery
• Uncontrolled diabetes mellitus, defined as HbA1c >8.5%, or severe endocrine or metabolic disorder
• Immunosuppression or active infection
• Rheumatologic shoulder involvement
• Neurological disease affecting shoulder movements
• Pregnancy
• Active malignancy

Individual participant data will not be shared due to privacy and ethical restrictions.

Participants and the outcomes assessor will be blinded to treatment allocation.