Internal impingement syndromes.

Internal causes of impingement are secondary to rotator cuff and capsular dysfunction and are categorized by the location of the impingement and the underlying pathophysiological or mechanical cause of the impingement. These include posterosuperior impingement, anterosuperior impingement, anterior impingement, and entrapment of the long head of the biceps tendon. The objective of this article is to review magnetic resonance imaging findings of each of the 4 types of internal impingement syndromes and discuss the pathophysiology behind the impingement.