Atlas of Human Anatomy by Netter

FACTS & HINTS

High-Yield Facts

Clinical Points
Disc Herniation

Protrusion of the nucleus pulposus through the annulus fibrosus:

Ninety-five percent at the L4/5 or L5/S1 level

Usually posterolateral herniation where annulus is thinnest

Herniation into the vertebral canal may compress the nerve root below the disc and cause pain in the related dermatome

Age-related dehydration of nucleus pulposus contributes to loss of height and narrowing of IV foramina

Lumbar Spinal Stenosis

Narrowing of the vertebral canal

Compression of spinal cord caused by age-related degenerative changes such as bulging of the IV discs or arthritis

Surgical laminectomy or removal of the entire vertebral arch may be necessary to alleviate symptoms

Clinical Points

Spinal cord development: In the fetus, the spinal cord extends down to the sacral vertebrae. As a fetus matures, the cord shortens relative to

the rest of the body, so at birth the conus medullaris reaches the L2/3 level, and by adulthood only around the level of the L1/2 IV disc, where

the cauda equina begins

Epidural block: Anaesthetic injected into epidural space of the sacral canal either via the sacral hiatus (caudal epidural) using the sacral

corneae as landmarks, or via the posterior sacral foramina (transsacral epidural). The anesthetic solution spreads superiorly to act on

spinal nerves S2-Co. The height to which the anesthetic ascends is affected by the amount of solution injected and the position of the

patient.

Spinal block: Introduction of an anesthetic directly into the CSF (in the subarachnoid space) utilizing a lumbar puncture (see above). Onset

of anesthesia is rapid <1 minute (unlike epidural anesthesia that may take up to 20 minutes). Subsequent leakage of CSF may cause a

headache in some individuals.

Mnemonics

Memory Aids

Dermatomes: T-ten over your belly but-ten

L3 over the knee

Sit on Sacral dermatomes