Imaging description

The constellation of findings of undersurface tears of the supraspinatus or infraspinatus tendon and cystic changes in the posterior aspect of the humeral head associated with posterosuperior labral pathology is a consistent finding diagnostic of internal impingement (Figures 15.1 and 15.2).

Importance

Internal impingement, also known as posterosuperior impingement, is a condition that occurs in athletes in which the shoulder is put in extreme abduction and external rotation during overhead movements.

Typical clinical scenario

Impingement of the rotator cuff on the posterosuperior glenoid labrum is a cause of posterior shoulder pain in athletes who throw. Patients present with posterosuperior shoulder pain that is sometimes associated with anterior instability.

Differential diagnosis

Cystic lesions are commonly visible in the posterosuperior portions of the humeral heads, the bare areas, just posterior to the greater tuberosity on shoulder MR images. Posterior cyst-like changes along with the changes in the rotator cuff and posterosuperior labrum should suggest internal impingement. Intraosseous humeral cysts in the posterior aspect of the greater tuberosity that communicate with the joint would appear to be incidental findings.

Teaching point

MR arthrography may allow detection of abnormalities associated with internal impingement.