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).
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Clinical presentation
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.
Pathology
An extreme abduction and external rotation (ABER) position 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.
Radiographic features
Plain radiograph / CT
Features include 4,6:
- greater tuberosity sclerosis and/or cysts
- posterior humeral head osteochondral lesions
- remodeling of the posterior glenoid rim
- Bennett lesion
MRI/MR Arthroscopy
Key features are 4-6:
- articular-sided tears of the posterior supraspinatus and anterior infraspinatus tendons
- posterosuperior labral tear or fraying or type IIB SLAP tear
- humeral head cysts underlying the infraspinatus tendon
Additional features include 4:
- anterior capsule laxity
- posterior capsule thickening
Practical points
- tears are more conspicuous in the ABER position ref
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