- 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