Subacromial impingement syndrome (SAIS) is a commonly diagnosed disorder of the shoulder. Though this disorder has been known for a long time, it remains a poorly understood entity. Over the years several hypotheses have been put forward to describe the pathogenesis of SAIS but no clear explanation has been found. Two mechanisms, the extrinsic and intrinsic mechanism, have been described for the impingement syndrome. The intrinsic mechanism theories which deny the existence of impingement are gaining popularity in recent years. The various shoulder tests used to diagnose SAIS have low specificity with an average of about 50%. Meta-analysis shows that neither the Neer sign nor the Hawkins sign has diagnostic utility for impingement syndrome. Several randomised controlled trials have shown that the outcome of treatment of SAIS by surgery is no better than conservative treatment. Physiotherapy alone can provide good outcome which is comparable to that achieved with surgery without the costs and complications associated with surgery. Since decompression with surgery does not provide any additional benefits as compared to conservative treatment for patients with SAIS, the impingement theory has become antiquated and surgical treatment should have no role in the treatment of such patients. There are calls by some practitioners to abandon the term impingement syndrome and rename it as anterolateral shoulder pain syndrome. It appears that SAIS is a medical myth. There are others who called SAIS as a clinical illusion.
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