Shoulder tendinopathy is a common condition that causes shoulder pain and limits daily activities. It often results from damage or overuse of the rotator cuff tendons. Treatment typically includes rest, physical therapy, anti-inflammatory medications, and sometimes injections. This clinical trial aims to compare the effectiveness of two types of injections for treating simple shoulder tendinopathy: Corticosteroid injections, which reduce inflammation and provide quick pain relief, but may have only short-term effects. Platelet-Rich Plasma (PRP) injections, a newer treatment made from the patient's own blood, which may promote long-term healing. The study is being conducted at the Rheumatology Department of Charles Nicolle Hospital in Tunis, Tunisia. A total of 60 adult patients with shoulder tendinopathy will be randomly assigned to receive either a corticosteroid injection or a PRP injection. Participants will be evaluated before the injection (baseline), after one week, and after three months. The researchers will assess pain levels using a visual analog scale (VAS), and shoulder function using validated questionnaires (DASH and SPADI scores). The goal is to determine which treatment provides better pain relief and functional improvement over time.