Houston Methodist. Leading Medicine

Shoulder FAQ


I have just been diagnosed with a subacromial impingement syndrome. I didn't injure myself that I can remember. It just started to come on gradually. First I noticed my arm wasn't moving all the way up. Then it started clicking and popping. Now I have pain that really bothers me the most at night. I'm racking my brain for what might have caused this. Any ideas?


One of the most common causes of shoulder pain is this problem you mentioned: subacromial impingement syndrome or SIS. The term impingement tells us something is getting pinched. Subacromial impingement syndrome occurs when the rotator cuff tendons rub against the roof of the shoulder, the acromion. Although SIS is one term, it actually represents a wide range of underlying pathologies. There could be a bursitis, rotator cuff tendinopathy, fracture, calcific tendinitis, or other change in the local anatomy contributing to the problem. There are many factors that when present combine together to result in subacromial impingement syndrome. Aging with its many degenerative processes isn't always very kind to the shoulder. Bone spurs form, the rotator cuff and other soft tissues fray and wear thin, and trauma all add to the development of mechanical shoulder pain. Loss of blood supply to the area is another reason why these problems occur. Subacromial impingement syndrome and rotator cuff degeneration go hand-in-hand together. Much debate and controversy exist over the connection between these two conditions. Which comes first? Does the impingement cause tearing of the rotator cuff? Or does the rotator cuff degenerate and weaken over time resulting in impingement? Sometimes there are what we call intrinsic factors such as muscle overload and weakness, shoulder overuse, and repetitive tissue microtrauma contributing to the problem. The shape of the bony structures of the shoulder (acromion, clavicle or collar bone, shoulder socket, round head of the humerus that fits into the socket) may have something to do with how the condition gets started. Imaging tests such as X-rays and MRIs may help identify some of the intrinsic anatomical factors that put people at increased risk for shoulder impingement. In many cases, it's really multifactorial with anatomy, age, and activity combined together to result in this problem. Marwan Alqunaee, RCSI, et al. Diagnostic Accuracy of Clinical Tests for Subacromial Impingement Syndrome: A Systematic Review and Meta-Analysis. In Archives of Physical Medicine and Rehabilitation. February 2012. Vol. 93. No. 2. Pp. 229-236.

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