Explain the pathophysiology of rotator cuff disorders, focusing on calcific supraspinatus tendinitis and subacromial bursitis, including diagnostic signs like Dawbarn's sign and the significance of th

Rotator cuff disorders are a common cause of shoulder pain, often involving calcific supraspinatus tendinitis or subacromial bursitis due to repetitive arm use. Calcium deposits can irritate the subacromial bursa, leading to inflammation. This causes pain, especially during 60°-120° of abduction (known as painful arc syndrome), as the bursa gets impinged. Dawbarn's sign helps diagnose subacromial bursitis: pain is felt when pressing below the acromion with the arm adducted, but not abducted, because the bursa slips away.