Shoulder impingement, or shoulder impingement syndrome, is a very common cause of shoulder pain, where the supraspinatus tendon (one of the rotator cuff tendons) inside your shoulder joint rubs or catches on nearby tissue (bursa) and bone (acromion) as you lift your arm.
Shoulder impingement is an old term that gave the impression that pain was caused by the rotator cuff tendon and bursa being pinched between the humeral head and acromion and we now realise that this is an oversimplification, and that pain can happen with no mechanical problem, so it is now referred to as Subacromial Shoulder Pain.
It affects the rotator cuff tendon, which connects the muscles around your shoulder joint to the top of your arm. Problems with the rotator cuff tendon can cause pain, the subacromial bursa or both. Rotator cuff tendon problems that can cause subacromial pain include rotator cuff tendinopathy, partial-thickness rotator cuff tears, and calcific tendonitis. Subacromial bursitis is the main bursal problem.
Pain in the shoulder will often improve in a few weeks or months, especially with the right type of shoulder exercises, but occasionally it can be an ongoing problem.