Serratus posterior superior is a thin, quadrilateral muscle in the upper posterior thorax deep to the rhomboids, attaching from the lower cervical and upper thoracic spinous processes to the upper ribs. Its accessory respiratory function is modest, and it is thought to contribute primarily to proprioception rather than force generation in quiet breathing. It is one of the most commonly described trigger point muscles in posterior thoracic and interscapular pain.
| Origin | Ligamentum nuchae and spinous processes of C7-T3, via a thin aponeurosis |
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| Insertion | Outer surfaces of ribs 2-5, just lateral to their angles |
| Nerve Supply | Anterior rami of thoracic spinal nerves T1-T4 (intercostal nerves) |
| Blood Supply | Posterior intercostal arteries (2nd-5th) |
| Actions | Elevates the upper ribs during forced inspiration; May assist external rotation of the upper ribs |
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Serratus posterior superior is a frequent source of trigger points producing deep interscapular and posterior shoulder pain that is difficult to localise. Trigger points in this muscle refer pain to the posterior shoulder, medial scapular border, and the medial arm in a pattern resembling C8 radiculopathy. Dry needling, IASTM, and stretching of the upper thoracic spine are effective treatments. The muscle is identified during surgical approaches to the posterior thorax by its position deep to the rhomboids.
Accessed by retracting the rhomboid major and minor medially to reach the deep surface beneath the medial scapular border at the T1-T4 level. Trigger points are palpated as taut bands deep to the rhomboids.
Myofascial pain from trigger points in the muscle producing deep interscapular and posterior shoulder aching, occasionally radiating to the medial arm, responsive to dry needling and thoracic mobility exercises.
