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• The anterior and posterior longitudinal ligaments reinforce the
  underlying annulus fibrosus but do not meet posterolaterally, resulting
  in a weak area predisposed to intervertebral disk herniation.


• Lumbar puncture and intrathecal anesthesia should be introduced
  below the third lumbar vertebra as the spinal cord usually terminates
  between the first and second lumbar vertebrae.


• Posterolateral disk prolapseimpinges on the spinal nerve of the next
  lower vertebral level, causing symptoms associated with the dermatomic
  and myotomal distributions of that nerve.

46 Anatomy, Histology, and Cell Biology

C3–C4 C4 Weak diaphramatic

(Phrenic, C3–C5) respiration

C4–C5 C5 Weak arm abduction

(Suprascapular, C4–C6)

C5–C6 C6 Weak forearm flexion Biceps

(Musculocutaneous,

C5–C6)

C6–C7 C7 Weak forearm extension Triceps

(Radial, C6–C8)

C7–C8 C8 Weak thumb adduction

(Ulnar, C7–T1)

L1–L2 L2 Weak hip flexion Cremaster

(Genitofemoral, L1–L2)

L2–L3 L3 (Obturator, L2–L4) Weak hip adduction

L3–L4 L4 (Femoral, L1–L4) Weak leg extension Knee jerk

L4–L5 L5 (Fibular, L4–S1) Weak dorsiflexion

L5–S1 S1 (Tibial, L5–S2) Weak plantar flexion Ankle jerk

HERNIATED DISK INVOLVEMENT, SIGNS,AND REFLEX TEST

Hernia Involvement Signs Reflex Test

LOWER EXTREMITY

Upper lateral No major vessels or nerves; A preferred

location for intramuscular injection

Upper medial Superior gluteal neurovascular bundle Abductor lurch

Lower lateral Inferior gluteal neurovascular bundle Difficulty climbing stairs

or rising from a chair

Lower medial Sciatic nerve Foot-drop

NEUROVASCULAR CONTENTS OF THE BUTTOCK

Quadrant Contents Symptoms