Anatomy Back Overview

Describe the composition of the vertebral column.

33 vertebrae organized into five regions: cervical, thoracic, lumbar, sacral, and coccygeal.

How many vertebrae are there?

33

What are the five regions of the vertebral column?

Cervical, thoracic, lumbar, sacral, and coccygeal

What are the primary curvatures of the vertebral column?

Thoracic and sacral kyphoses

What parts of the vertebral column are present at birth?

The primary curvatures; the thoracic and sacral kyphoses

What are the secondary curvatures of the vertebral column?

Cervical and lumbar lordoses

When does the secondary curvatures of the vertebral column develop?

They develop with head control, sitting, standing, and walking.

What are the core functions of the vertebral column?

It protects the spinal cord, supports body weight, maintains posture, and provides a flexible body axis.

What word describes abnormal lateral curvature with vertebral rotation; may be iodiopathic, congenital, or neuromuscular?

Scoliosis

What word describes excessive thoracic curvature; clinically associated with osteoporosis, vertebral compression fractures, and aging?

Kyphosis

What word describes excessive lumbar curvature; may be associated with pregnancy, obesity, weak abdominal musculature, or hip flexion contracture?

Lordosis

What is the clinical application to spinal deformities?

Deformities can alter biomechanics, compress neural structures, and contribute to chronic pain.

Anterior, weight-bearing compnent that increases in size from cervical to lumbar regions.

Vertebral body

What is formed by pedicles and laminae; encloses the vertebral foramen?

Vertebral arch

One spinous, two transverse, and four articular processes for muscle attachment and joint formation.

Processes

Plane synovial joints between superior and inferior articular processes.

Zygapophysial/facet joints

_______ removes part of the lamina to decompress the spinal cord or nerve roots.

Laminectomy

Typical _____ vertebrae have transverse foramina and often bifid spinous processes.

cervical

Lacks a body and spinous process; articulates with occipital condyles for “yes” nodding movement.

C1 Atlas

Contains the dens/odontoid process; pivot for “no” rotation at the atlanto-axial joint.

C2 Axis

Long, palpable spinous process; an important surface landmark.

C7 Vertebra prominens

Burst fracture of the C1 ring, often due to vertical compression.

Jefferson fracture

Commonly occurs at the base of the dens; may be unstable due to transverse ligament involvement and limited blood supply.

Dens fracture

Traumatic spondylolysis of C2, classically caused by hypertension.

Hangman’s fracture

Rapid hyperextension/flexion injury that may damage cervical ligaments and soft tissues.

Whiplash

Transverse ligament of the atlas, alar ligaments, cruciate ligament, and tectorial membrane.

Key stabilizer

Heart-shaped bodies and costal facets for rib articulation.

Thoracic vertebrae T1-T12

Relatively limited flexion/extension because of the rib cage; rotation is more pronounced than in lumbar spine.

Thoracic region

Massive kidney-shaped bodies adapted for weight-bearing.

Lumbar vertebrae L1-L5

Allows flexion and extension; limited rotation due to facet orientation.

Lumbar region

What may compress the cauda equina or exiting nerve roots?

Lumbar spinal stenosis

Five fused vertebrae that transmit weight from the vertebral column to the pelvic girdle.

Sacrum

Continuation of the vertebral canal; contains sacral nerve roots.

Sacral canal

Inferior opening of the sacral canal and landmark for caudal epidural anesthesia.

Sacral hiatus

Typically four small fused vertebrae; attachment site for the filium terminale and pelvic floor/gluteal structures.

Coccyx

Permit movement and absorb compressive forces between vertebral bodies.

IV discs

Concentric fibrocartilage rings that resist tension and contain the nucleus pulposus.

Anulus fibrosis

Gelatinous core that distributes pressure within the disc.

Nucleus pulposus

Resists hyperextension and strengthens the anterior vertebral column.

Anterial longitudinal ligament

Resists hyperflexion but is narrower, allowing posterolateral disc herniation.

Posterior longitudinal ligament

Elastic ligament connecting laminae; assists return to upright posture.

Ligamentum flavum

Occurs when nucleus pulposus protrudes through a tear in the anulus fibrosus.

Disc herniation

Why are posteriolateral herniations common?

The anulus is weaker and less supported by longitudional ligaments in this region.

Where do most lumbar disc protrusions occur?

At L4-L5 or L5-S1

What is the General lumbar rule?

An L4-L5 disc herniation compresses the L5 nerve root; an L5-S1 herniation compresses the S1 nerve root.

Low back/hip pain radiating down the posterior thigh and leg due to sciatic nerve component irritation.

Sciatica

What should you say that is more anatomically accurate than saying “slipped disc”?

“Herniated” or “ruptured” disc

Where does the spinal cord extend?

It extends from the medulla to the conus medullaris, usually at L1-L2 in adults.

_____ enlargement supplies the upper limbs; _______ enlargement supplies the lower limbs.

Cervical; lumbosacral

Descending lumbar, sacral, and coccygeal nerve roots below the conus medullaris.

Cauda equina

Pial extension anchoring the spinal cord inferiorly to the coccyx.

Filum terminale

What allows safer lumber puncture below L2 because mobile nerve roots can be displaced by the needle?

The cauda equina

Tough outer meningeal layer forming the dural sac.

Dura mater

Web-like, avascular middle layer.

Arachnoid mater

Delicate inner layer closely adherent to the spinal cord.

Pia mater

Contains cerebrospinal fluid and extends inferiorly as the lumbar cistern.

Subarachnoid space

Contains fat and the interal vertebral venous plexus.

Epidural space

Lateral pial extensions that help suspend the spinal cord within the dural sac.

Denticulate ligaments

Needle enters the subarachnoid space/lumbar cistern, typically at L3-L4 or L4-L5.

Lumbar puncture

Line across the iliac crests approximates the L4 spinous process or L4-L5 interspace.

Crista line/Tuffier’s line

Anesthetic injected into CSF in the subarachnoid space.

Spinal block

Anesthetic injected into the epidural space; may also be administered through the sacral hiatus as a caudal epidural.

Epidural block

Accidental dural puncture during epidural placement can cause what?

CSF leakage and post-dural puncture headache

What three longitudinal arteries supply the spinal cord?

One anterior spinal artery and paired posterior spinal arteries

Formed by branches of the vertebral arteries, runs in the anterior median fissure.

Anterior spinal artery

Arise from the anterior spinal artery and supply much of the cord cross-sectional area.

Sulcal arteries

Reinforce longitudinal supply; arise from vertebral, deep cervical, intercostal, lumbar, and lateral sacral arteries.

Segmental medually arteries

Major contributor to the lower two-thirds of the spinal cord.

Great anterior segmental artery of Adamkiewicz

Valveless and can provide a route for metastasis.

Internal and external vertebral venous plexuses

Primarily move the upper limb and ribs rather than the vertebral column itself.

Extrinsic muscles

Trapezius, latissimus dorsi, levator scapulae, and rhomboids

Superficial layer

Functions of the muscles of the back

Scapular elevation, retraction, depression, rotation, and humeral extension/adduction

Serratus posterior superior and serratus posterior inferior

Intermediate layer

Which muscles of the back contribute to respiration and proprioception?

Intermediate muscles

Innervated by posterior rami of spinal nerves and act on the vertebral column/head.

Intriscic muscles of the back

Splenius capitis and splenius cervicis

Superficial intrinsic layer

Erector spinae group - iliocostalis, logissimus, and spinalis

Intermediate intrinsic layer

Transversospinalis group - semispinalis, multifidus, and rotatores

Deep intrinsic layer

What are the primary functions of the intrinsic group of the back?

Extension, lateral flexion, rotation, posture, and segmental stabilization

A 50-year-old male presents with acute low back pain and numbness in the lateral foot after lifting a heavy object. Which anatomical structure is most likely compromised?

The S1 nerve root, typically due to a herniated L5-S1 intervertebral disc.

A 50-year-old male presents with acute low back pain and numbness in the lateral foot after lifting a heavy object. At which vertebral level is this most likely occuring?

Most likely at the L5-S1 intervertebral level

A 50-year-old male presents with acute low back pain and numbness in the lateral foot after lifting a heavy object. Which nerve root is most likely affected and why?

S1 because it contributes to sensation along the lateral aspect of the foot and controls the plantarflexion muscles.

A 50-year-old male presents with acute low back pain and numbness in the lateral foot after lifting a heavy object. Why is a lumbar puncture generally safe at the L4 level in this patient?

The spinal cord usually ends around L1-L2 in adults. Below this level, the vertebral canal contains mainly the cauda equina - individual nerve roots suspended in cerebrospinal fluid. These nerve roots are relatively mobile and tend to move away from a needle, making injury less likely.