📝 STANDARD DESCRIPTION:
SCIATIC NERVE (L6-S2): LARGEST nerve of the body.
- Exits pelvis via greater sciatic foramen, passes caudal to greater trochanter, runs down caudal thigh.
- Splits at stifle into:
1. TIBIAL NERVE (caudal branch):
- Runs down BACK of leg (with gastrocnemius).
- Supplies: hamstrings + GASTROCNEMIUS + SDF + DDF.
- Damage → cannot extend hock; 'dropped hock'.
- BLOCK SITE: Medial side of the hock just above the calcaneus.
2. PERONEAL (FIBULAR) NERVE (cranial branch):
- Wraps around lateral side of stifle (head of fibula) — VULNERABLE!
- Runs down FRONT of leg.
- Supplies: tibialis cranialis + long digital extensor (hock flexors).
- Damage → cannot lift foot; toe drags → 'knuckling'.
- BLOCK SITE: Lateral side of leg, just below head of fibula.
📚 DETAILED DESCRIPTION:
SCIATIC NERVE — KING OF NERVES
The sciatic is the LARGEST nerve of the body. It carries motor and sensory fibres for almost the whole hindlimb below the stifle.
COURSE: Origin from L6-S1-S2 → exits pelvis via the greater sciatic foramen → passes caudal to the greater trochanter of femur → runs down between the hamstring muscles → at the level of the stifle, splits into 2 terminal branches:
• Tibial (caudal branch).
• Common Peroneal/Fibular (cranial branch).
TIBIAL NERVE:
• Runs deep on the caudal aspect of the leg between the heads of gastrocnemius.
• Supplies: hamstrings (in part), gastrocnemius, SDF, DDF, popliteus → all extensors of hock + flexors of digits.
• Sensory: skin of back of leg, plantar aspect of foot.
• BLOCK SITE in horse: Medial aspect of hock, just above the calcaneus, on the anterior border of the calcaneal tendon → the nerve is felt as a soft band (TIBIAL NERVE BLOCK = part of 'high four-point' in hindlimb diagnostic blocks).
• Damage → cannot extend hock → animal stands with hock dropped, fetlock knuckles.
COMMON PERONEAL NERVE (Fibular Nerve):
• Wraps SUPERFICIALLY around the lateral side of stifle (over head of fibula) — only skin and a thin layer of muscle cover it here → very vulnerable to direct trauma & to compression when an animal lies on its side.
• Splits into superficial and deep peroneal branches.
• Supplies: tibialis cranialis, long digital extensor, peroneus tertius (in dog), lateral digital extensor → hock flexors + digital extensors.
• Sensory: skin of dorsum of foot.
• BLOCK SITE in horse: Lateral side of leg, between the long and lateral digital extensors, just below the head of fibula → PERONEAL NERVE BLOCK.
• Damage → cannot lift foot → toe drags ('knuckling at the fetlock'). Common in cattle after recumbency on hard ground.
PLANTAR NERVE BLOCK: Done at the level of the fetlock on plantar surface of the metatarsus (medial & lateral plantar nerves) — used to anaesthetise the digit (similar to palmar nerve block in forelimb).
// COMPARATIVE ANALYSIS
| HORSE |
Tibial and Peroneal nerve blocks are part of the diagnostic anaesthesia for hindlimb lameness. |
| CATTLE |
Peroneal nerve compression on hard concrete floors causes knuckling — common 'downer cow' complication. |
| DOG |
Sciatic damage from pelvic fractures or wrong-site IM injection in caudal thigh. |
CLINICAL RELEVANCE
UG SYLLABUS NERVE BLOCKS — hindlimb sites:
• Tibial Block: Medial hock, above calcaneus (anterior to Achilles tendon).
• Peroneal Block: Lateral leg, just below head of fibula.
• Plantar Block: Plantar surface of fetlock (medial + lateral plantar nerves).
Peroneal Paralysis (cattle): Cow recumbent on concrete → toe drags when trying to walk. Pad floors well.
