📝 STANDARD DESCRIPTION:
High-Yield Points:
• Last thoracic (T13) + Lumbar (L1-L6) ventral rami form the lumbar plexus.
• Key nerves to abdominal wall:
– T13 = costoabdominal nerve (last intercostal, supplies caudal flank).
– L1 = iliohypogastric (iliocostal) nerve — to flank skin & muscle.
– L2 = ilioinguinal — to caudal flank, prepuce/udder.
– L3-L4 = genitofemoral — to scrotum/udder, cremaster.
• Paravertebral nerve block targets T13, L1, L2 (proximal) at transverse process emergence — desensitises the flank.
📚 DETAILED DESCRIPTION:
LUMBAR PLEXUS — NERVES OF THE FLANK
The lumbar plexus is formed by the ventral rami of the last thoracic (T13) and the first six lumbar nerves (L1-L6). It lies within the substance of the psoas major muscle.
NERVES SUPPLYING THE ABDOMINAL WALL (top to bottom):
1. T13 — Costoabdominal nerve: Runs along caudal border of last rib; supplies skin and muscles of the cranial flank.
2. L1 — Iliohypogastric (cranial iliac) nerve: Crosses ventro-laterally; pierces the abdominal muscles to supply skin & muscle of the mid flank including paralumbar fossa.
3. L2 — Ilioinguinal (caudal iliac) nerve: Crosses lower; supplies caudal flank, skin around the prepuce/udder, and contributes to inguinal region.
4. L3-L4 — Genitofemoral nerve: Two branches:
• Genital branch — through inguinal canal to scrotum/udder (cremaster reflex).
• Femoral cutaneous branch — to skin of medial thigh.
5. L4-L5 — Femoral nerve (hindlimb).
6. L5-L6 — Obturator nerve (hindlimb).
7. L6-S2 — Lumbosacral trunk → Sciatic nerve (hindlimb).
PARAVERTEBRAL NERVE BLOCK — used for standing flank surgery (rumenotomy, LDA, caesarean):
Proximal Paravertebral (Farquharson / Cambridge technique):
• Blocks T13, L1, L2 spinal nerves where they emerge between vertebrae.
• Needle inserted dorsally beside spine, passed cranio-laterally just under the transverse process.
• ~10-15 mL 2% Lidocaine per nerve.
• Advantages: complete flank desensitization, small volume, no muscle weakness in limbs.
Distal Paravertebral (Magda technique):
• Same nerves but blocked at the tip of the transverse processes (L1, L2, L4) — easier landmarks but less reliable.
Inverted-L Block: Simple line infiltration along last rib + ventral to lumbar transverse processes — easy, but uses more anaesthetic.
// COMPARATIVE ANALYSIS
| OX |
Paravertebral block of T13, L1, L2 = standard for flank laparotomy. Tuber coxae line guides the operator. |
| HORSE |
Paravertebral less common — most flank surgery done under general or with infiltration. |
| DOG |
Lumbar plexus blocks done by ultrasound for hindlimb surgery. |
CLINICAL RELEVANCE
Paravertebral Nerve Block: The 'gold standard' regional anaesthesia for cattle standing flank surgery. Loss of muscle tone causes scoliosis to the desensitized side — a confirmation of successful block. Genitofemoral block: For udder surgery in cow.
