The infraspinatus is the primary external rotator and is the second most commonly torn rotator cuff muscle. Its middle facet footprint is just posterior to the supraspinatus footprint on the greater tuberosity.
| Origin | Infraspinous fossa — medial two-thirds |
|---|---|
| Insertion | Greater tuberosity — middle facet (the second footprint) |
| Nerve Supply | Suprascapular nerve (C5, C6) |
| Blood Supply | Suprascapular and circumflex scapular arteries |
| Actions | External rotation of the glenohumeral joint — primary external rotator; Posterior glenohumeral stabilisation; Assists shoulder extension from flexion |
|---|
Infraspinatus isolation is tested by resisted external rotation with the arm at the side. In posterior shoulder instability, infraspinatus strengthening is the primary rehabilitation strategy. Isolated infraspinatus tears from suprascapular nerve entrapment at the spinoglenoid notch produce selective external rotation weakness without supraspinatus involvement.
Tested by resisted external rotation at 0 degrees of abduction.
Suprascapular nerve entrapment at the spinoglenoid notch producing selective infraspinatus denervation with external rotation weakness and posterior shoulder pain, treated by ganglion cyst excision or notch decompression.
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