Posterosuperior impingement of the shoulder
Posterosuperior impingement, also known as internal impingement, is a relatively uncommon form of shoulder impingement primarily involving the infraspinatus tendon and the posterosuperior glenoid labrum. It occurs when the shoulder is abducted and externally rotated (ABER position).
Patients present with posterior shoulder pain and instability. It almost exclusively occurs in athletes who repetitively place their shoulder into extreme abduction and external rotation such as throwers, swimmers, volleyball players and tennis players.
The extreme abduction and external rotation results in repeated impingement of the infraspinatus tendon and the posterior portion of the supraspinatus tendon between the head of the humerus and the posterior superior rim of the glenoid. There is resulting tendon degeneration, reactive humeral head cysts, and glenoid labrum degeneration.
- infraspinatus tendinosis and tears, usually superior fibers at the humeral surface
- supraspinatus tendinosis and tear involving the posterior fibers
- posterosuperior labral tear or fraying
- tears are more conspicuous in the ABER position
- humeral head cysts underlying the infraspinatus tendon
- partial articular supraspinatus tendon avulsion (PASTA) lesion: articular-surface rim rent at the tendon footprint on the greater tuberosity
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