The subcostal nerve is the ventral ramus of the T12 spinal nerve, running below the twelfth rib in the subcostal groove. Unlike the true intercostal nerves (T1-T11), the subcostal nerve has no rib above it. It passes anterior to the quadratus lumborum, pierces the transversus abdominis, and runs between the transversus abdominis and internal oblique to supply motor fibres to the anterior abdominal wall muscles and cutaneous sensation to the skin just above the iliac crest and the lateral buttock.
| Origin | Anterior ramus of T12 |
|---|---|
| Course | Runs along the lower border of the twelfth rib, passes behind the lateral arcuate ligament and anterior to quadratus lumborum, then continues between transversus abdominis and internal oblique to the anterior abdominal wall |
| Motor |
|
| Sensory |
|
The subcostal nerve is injured during nephrectomy and posterior retroperitoneal approaches when the incision extends below the twelfth rib, producing a localised area of anaesthesia and weakness above the iliac crest. It is blocked as part of abdominal field blocks for postoperative analgesia following upper abdominal and flank surgery. Subcostal nerve entrapment produces iliac crest pain and can mimic hip pathology. The nerve's course between transversus and internal oblique makes it relevant in transversus abdominis plane (TAP) blocks.
Incisions below the twelfth rib for nephrectomy, adrenalectomy, or retroperitoneal approaches risk injury to the subcostal nerve, producing an area of sensory loss above the iliac crest and a bulge from weakened lateral abdominal musculature that may persist or gradually improve over months as the nerve regenerates.
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