Shoulder pain is the third most common musculoskeletal complaint and "impingement" is the most common diagnosis. Typical symptoms of shoulder impingement include pain when lifting your arm or lowering it from a raised position, pain when reaching, and pain or achiness at night especially when lying on the affected side.
Traditionally it was thought that these symptoms were caused by a narrowing of the 'subacromial space', which is the space in the shoulder joint where the rotator cuff tendons and bursa are found. This narrowing causes them to ‘impinge’ against the underside of the bony shelf that forms the top of the shoulder joint - the 'acromion'. This idea led to a number of treatments that are aimed at reducing the impingement by increasing the subacromial space, including surgical decompression where more space is created by removing some of the bone from the top of the joint.
However, a Cochrane review published in 2019 found that there is high-certainty that subacromial decompression surgery does not provide any benefits in pain, function, or quality of life when compared to placebo. Furthermore, another study published in 2021 by Paavola et al followed patients for 5 years after undergoing surgical decompression surgery and also found that there was no difference when compared to placebo surgery (sham or fake surgery).
How could this be? If the shoulder pain is caused by impingement and we reduce the impingement by increasing the space, why doesn't the pain improve?
A systematic review and meta-anaylsis published in 2020 answered that very question. They analyzed all the studies investigating shoulder pain caused by subacromial impingement and found that there was actually no difference in the amount of subacromial space in people who had shoulder pain caused by "impingement" and people who did not have any shoulder pain.
The authors of the Paavola study go so far as to declare that "the impingement theory has become antiquated" and that "the term 'Shoulder Impingement' should be abandoned." Instead we should refer to pain in this area simply as 'Subacromial Pain'.
So what do we do about it? Good News! A systematic review published in 2020 in the Journal of Orthopaedic and Sports Physical Therapy concluded that the best treatment for Subacromial Pain is exercise, the exercise program should include resistance exercises, and that manual therapy is beneficial when used in conjunction with the exercise program. Unfortunately there is no quick fix and the expected duration of rehab is 12 weeks. Patience is a virtue!