Lecture on Lumbar Plexus and Sacral Plexus

Introduction

• Focus on lower extremity nerve supply: pelvis and perineal area.
• Central Nervous System (CNS): brain and spinal cord.
• Peripheral Nervous System (PNS): cranial nerves and spinal nerves.

Spinal Nerves Overview

• 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal.
• Mixed nerves: sensory and motor.
• Spinal nerve divides into dorsal and ventral ramus.
  • Dorsal ramus: minor role, supplies back skin/muscles.
  • Ventral ramus: forms plexuses, more significant.

Lumbosacral Plexus

• Composed of lumbar plexus and sacral plexus.
  • Lumbar Plexus: L1-L4, key nerves are obturator and femoral.
  • Sacral Plexus: L4-S4, key nerves are sciatic and pudendal.

Lumbar Plexus

• Obturator Nerve: anterior divisions of L2-L4.
• Femoral Nerve: posterior divisions of L2-L4.
• Additional branches: iliohypogastric, ilioinguinal, genitofemoral, lateral femoral cutaneous.

Sacral Plexus

• Sciatic Nerve: largest nerve, composed of tibial and common fibular nerves.
  • Tibial nerve (anterior divisions of L4-S3)
  • Common fibular nerve (posterior divisions of L4-S2)
• Superior and Inferior Gluteal nerves, nerve to piriformis.

Muscle Innervations

• Thigh Compartments:
  • Anterior: femoral nerve (quadriceps, sartorius).
  • Medial: obturator nerve (gracilis, adductors).
  • Posterior: sciatic nerve (hamstrings).
• Leg Compartments:
  • Anterior: deep fibular nerve (tibialis anterior, extensor muscles).
  • Lateral: superficial fibular nerve (fibularis muscles).
  • Posterior: tibial nerve (gastrocnemius, soleus).

Nerve Injuries

• Tibial Nerve Injury:
  • Affects plantar flexion.
  • Difficulty walking on tiptoes, downhill.
• Common Fibular Nerve Injury:
  • Affects dorsiflexion.
  • Causes foot drop, difficulty walking uphill.

Dermatomes and Clinical Signs

• Dermatomes: distribution of sensory nerves over skin regions.
• Tinel’s Sign: tingling when tapping a nerve.
• Trendelenburg Sign:
  • Superior gluteal nerve injury.
  • Pelvis tilts down on opposite side of standing leg.

Conclusion

• Understanding nerve pathways and muscle innervations is crucial for diagnosing nerve injuries.
• Anatomy makes sense with clear explanation.

Additional Resources

• Medicosis Perfectsnetis offers anatomy playlists and premium courses on surgical and emergency medicine topics.