Shoulder impingement revisited: advanced concepts of pathomechanics and treatment.

Subacromial impingement is a common disorder of the shoulder that is still poorly understood. Knowledge of the pathogenesis of this condition has expanded greatly since it was described by Neer 40 years ago. Research has shown that multiple factors contribute to the development of rotator cuff disease. New investigations are exploring this disorder with input from several scientific disciplines. It is essential that orthopaedic surgeons treating patients with subacromial impingement understand the underlying mechanisms, the new research, and the current trends in management of this disease.