High-frequency Short-course Extracorporeal Shock Wave Therapy for Partial Rotator Cuff Tears: Study Protocol for a Multicenter, Randomized, Controlled Trial

Inclusion Criteria: * Age 30-70 years, male or female * MRI- or high-resolution ultrasound-confirmed partial-thickness rotator cuff tear (predominantly supraspinatus) or small full-thickness tear without retraction or displacement * Shoulder pain duration ≥3 months with Visual Analog Scale (VAS) score ≥4 (0-10 scale) * Willing and able to provide written informed consent and comply with the study protocol Exclusion Criteria: * Large or massive full-thickness rotator cuff tear, tear with Grade II retraction or greater, or presence of a greater tuberosity bone cyst * Severe muscle fatty infiltration (Goutallier grade ≥3) on MRI * Uncontrolled diabetes mellitus (HbA1c \>7.5%), hypothyroidism, or heavy smoking (≥20 pack-years) * Received local injection therapy (e.g., corticosteroids, platelet-rich plasma) to the affected shoulder within 4 weeks prior to enrollment * Concurrent shoulder pathologies including glenohumeral osteoarthritis, adhesive capsulitis (frozen shoulder), or shoulder instability * Systemic diseases (e.g., rheumatoid arthritis), bleeding disorders, or coagulopathy * Pregnancy or lactation * Contraindications to ESWT (e.g., cardiac pacemaker, malignancy at treatment site) * Inability to complete treatment or follow-up schedule