Serratus posterior inferior is a thin respiratory muscle at the thoracolumbar junction. It depresses the lower ribs during forced expiration, acting as an antagonist to the diaphragm.
| Origin | Spinous processes of T11-L3 via the thoracolumbar fascia |
|---|---|
| Insertion | Lower borders of ribs 9-12 |
| Nerve Supply | Ventral rami of T9-T12 |
| Blood Supply | Posterior intercostal arteries |
| Actions | Depresses the lower ribs during forced expiration; Stabilises the lower thorax during trunk movements |
|---|
Serratus posterior inferior is a landmark for thoracolumbar junction surgery — its attachment to the lower ribs marks the transition between the thoracic and lumbar paraspinal compartments. It is encountered in the retroperitoneal approach to L1-L2.
Palpated at the posterior lower thorax over ribs 9-12 during forced expiration.
Identification of the serratus posterior inferior as the muscle layer marking the rib-paraspinal transition during retroperitoneal access to the thoracolumbar junction.
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