Transcutaneous Auricular Vagus Nerve Stimulation Added to Physiotherapy for Adhesive Capsulitis

Inclusion Criteria: * Age between 18 and 65 years. * Clinical diagnosis of adhesive capsulitis confirmed by physical examination and, when clinically indicated, imaging. * Shoulder pain and limitation of shoulder range of motion for at least 3 months. * Provision of written informed consent. * General health status sufficient to participate in standard physiotherapy and active or sham transcutaneous auricular vagus nerve stimulation. * Ability to comply with the planned treatment sessions and outcome assessments. Exclusion Criteria: * Shoulder stiffness secondary to trauma, surgery, infection, or tumor. * Rotator cuff tear, advanced glenohumeral osteoarthritis, or inflammatory rheumatic disease. * Glucocorticoid injection into the affected shoulder within the previous 3 months. * Surgical intervention involving the affected shoulder within the previous 6 months. * Active infection or skin lesion in the shoulder region. * Cervical radiculopathy, brachial plexopathy, stroke, or another neurological disorder affecting the upper extremity. * Presence of a cardiac pacemaker or another implanted electronic device. * Pregnancy or breastfeeding. * Serious systemic disease or cognitive impairment that may prevent compliance with the study protocol. * Known intolerance or previous adverse reaction to transcutaneous electrical stimulation.