External impingement of the shoulder

The relationship between external shoulder impingement and rotator cuff disease has been the subject of much research, but the theories of cause and effect remain controversial. Patients with symptoms of external impingement are referred for imaging to identify bony abnormalities of the coracoacromial arch and associated bursal and rotator cuff disease. Attempts have been made to identify objective imaging criteria that confirm the diagnosis of impingement, but at present external impingement remains primarily a clinical diagnosis. Therapeutic management varies from rehabilitation with physiotherapy to surgical procedures aimed at decompressing the subacromial space and repairing rotator cuff tears. This article reviews the relevant anatomy, biomechanics, and theories of external impingement, the role of imaging in the diagnosis of external impingement and rotator cuff disease, and implications upon management.