ANATOMY OF THE SPINE & EPIDURAL SPACE BY MAYURI GOLHAR

CONTENTS

VERTEBRAE LIGAMENTS EPIDURAL SPACE & ITS CONTENTS MENINGES CSF SPINAL CORD BLOOD SUPPLY OF THE SPINAL CORD

VERTEBRAE

The spine consists of 33 vertebrae With the exception of c1 the cervical, thoracic,

lumbar vertebrae consists of a body,2 pedicles which projects posteriorly from the body,2laminae that connects the pedicle.

The lamina give rise to the transverse process that project laterally & the spinous process that projects posteriorly

These structures form the vertebral canal which consists of spinal cord, spinal nerve & epidural space.

VERTEBRAE

cervical

thoracic

lumbar

sacral

coccyx

VERTEBRAE cont..

The pedicles contain superior & inferior notch from which the spinal nerve exits.

The sup & inf articular process arise at the junction of the lamina & pedicle & joins with the adjoining vertebra.

The atlas vertebra differs from this typical structure that it does not have a body & a spinous process.

The 5 sacral vertebra are fused together to form the wedge shaped sacrum, however the fifth sacral vertebra is not fused posteriorly so it gives rise to a opening known as sacral hiatus.

VERTEBRAE cont..

The sacral hiatus provides an opening in the sacral canal which is the caudal termination of the epidural space.

Identifying individual vertebra is imp for correctly locating the desired interspinous space for epidural & spinal blockage.

The spine of the C7 is the first prominent spinous process while running the hand down the back. The spine of T1 immediately follows C7. T12 can be located by identifying the 12th rib & tracing it back to its attachment to T12

VERTEBRAE cont..

The spine of the thoracic vertebra slopes steeply downwards & those of T5 T8 are almost vertical so that there tips lie at the level of the body of the vertebra below.

The spines of T1,T2,T11& T12 are almost horizontal while T3,T4,T9 &T10 are oblique.

The spine of lumbar vertebra is hatchet shaped & projects backwards almost horizontally.

VERTEBRAE cont..

The body of a typical thoracic vertebrae (1) is somewhat heart-shaped The vertebral foramen (5) is smaller and more circular.The transverse processes (3) long with the length diminishing as one moves caudally. The spinousprocesses (2)long and slope posteroinferiorly with the tip extending to level of vertebral body below.Clinical Pearl: With arms placed at the sides, the T7 level is usually at the same level as the inferior angle of the scapulae.

VERTEBRAE cont..

The body: is massive and kidney-shaped upon axial view.The vertebral foramen: is triangular and smaller transverse processes: are long and slender.The spinous processes: are short and sturdy.Clinical Pearl: A line drawn between the highest points of bothiliac crests usually crosses over the body of L4 or the L4-L5 interspace.

LIGAMENTS

The veretbral bodies are stabilized by 5 ligaments that increase in size between the cervical & lumbar vertebrae.

The supraspinous ligament runs from sacrum to T7, above T7 this ligament runs as ligamentum nuchae & attaches to the occipital protuberance.

The interspinous ligament attaches between spinous processes & blends post with the supraspinous lig. & anteriorly with the ligamentum flavum.

Ligamentum flavum is a tough, wedge shaped ligament composed of elastin.

LIGAMENTS

LIGAMENTS cont..

The ligamentum flavum is thickest in the midline measuring 3-5mm at the L2-L3 space.It is also farthest from the spinal meninges measuring 4-6mm at the L2-L3 space.

So midline insertion of the epidural needle is least likely to cause unintended meningial puncture.

LIGAMENTUM FLAVUM

MENINGES & LIGAMENTS

EPIDURAL SPACE

It is the space that lies between the spinal meninges & the sides of the vertebral canal.

It is bounded cranially by the foramen magnum, caudally the sacrococcygeal ligament, anteriorly by the post longitudinal ligament, laterally by the vert pedicles & post by both lig.flavum & vert.lamina

This space communicates with the parvertebal space by the way of intervertebral foramina.

The epidural space is shallowest anteriorly where the dura may fuse with the posterior long.ligament & it is deepest posteriorly.

EPIDURAL SPACE

EPIDURAL SPACE

EPIDURAL SPACE cont..

A rich network of valveless veins( BATSONS PLEXUS) courses through the ant & lat portions of epidural space.

The epidural veins anastomose freely with the veins connecting the head &pelvis.

Venous return from the pelvis passes through the extradural venous plexus to the azygos veins which drains into the IVC.

It also contains the lymphatics, segmental arteries & epidural fat.

EPIDURAL SPACE

In the cervical region the dimension is 1-2mm whereas in lumbar region it is 5-6mm

When the local anesthetic is injected it spreads as rivulets. The greater the volume of injectate the spread is more homogenous.

The epidural space consists of series of discontinous compartments that becomes continuous when the potential space is opened up by injection of air or liquid.

EPIDURAL FAT

It is the most abundant material in the epidural space located principally in the post& lat compartments

It plays an imp role in the pharmacology of epidurally & intrathecally administered drug.

There is a linear relationship between the opiods lipid solubility,terminal elimination & its conc in the epidural fat.

The more the drug is lipid soluble least is its transfer from the epidural to intrathecal space.

EPIDURAL SPACE

Compared to the lumbar level all the ligaments are lax at the thoracic level so the resistance offered by the advancing needle is not well felt

At the lumbar level the dura surrounds the nerve root of the cauda equina whereas at the thoracic level it surrounds the spinal cord itself so this reduces the safety margin of performing epidural at the thoracic level.

The margin of safety is more in the cervical level as the spinal canal is larger & the spinal cord doesn’t occupy it completely.

MENINGES

Spinal meninges consists of dura, arachnoid mater, & the pia mater.

DURA :outermost & thickest meningeal tissue. It begins at the foramen magnum & ends at S2

where it fuses with the filum terminale The dura is composed of randomly arranged collagen

fibres & elastin fibres arranged longitudinally & circumferentially.

The dura is largely acellular & the inner edge of the dura is highly vascular & that is why it is an imp route of clearance of the drugs injected in the epidural & subarachnoid space.

MENINGES cont…

The inner surface of the dura abuts the arachnoid mater. There is a potential space between these two membranes called the subdural space. Occasionally a drug may enter this space while intended epidural or subarachnoid injections.

ARACHNOID matter: it is delicate, avascular Consists of layers of flattened cells &connective tissue fibres. These cells contain frequent tight junctions & occluding junctions so it acts as a barrier for the drugs moving between the epidural space & the spinal cord.

MENINGES

DM- dura mater AM- arachnoid mater

MENINGES cont..

The aracnoid mater herniates through the dura into the epidural space to form the arachnoid granulations an serves for material in the SAS to exit the CNS.

Subarachnoid space: it is a space which lies between the arachnoid mater & piamater & contains CSF, spinal nerve root & rootlets.

MENINGES cont..

PIAMATER: it is adherent to the spinal cord & contains connective tissue cells interspersed with collegen. Piamater is fenestrated so that spinal cord is in direct communication with the SAS.

The piamater extends to the tip of spinal cord where it becomes the filum terminale which anchors the spinal cord to the sacrum.

CEREBROSPINAL FLUID

It is a complex solution containing electrolytes, proteins , glucose, neurotransmitters, cyclic nucleotides, aminoacids.

Produced by the choroid plexuses by ultrafilteration of plasma & oxidation of glucose.

volume: 100-160 ml. Rate of production: 20- 25ml/hr so the entire vol is

replaced in 6hrs It contains more amount of Na& Cl ion & less

amount of glucose & K. PH-7.32 CSF is removed by the arachnoid villi.

SPINAL CORD

In 1st trimester fetus spinal cord extends from the foramen magnum to the end of sacrum.

Thereafter the length of the vertebral canal lengthens more than the spinal cord so that at birth the spinal cord ends at the level of L3

In adults it ends at lower border of L1, however in 30% it may end at T12 & in 10% it may extend till L3.

Its continous at the upper end with the medulla oblongata & below with the conus medullaris from which the filum terminale descends as far as the coccyx

SPINAL CORD cont..

Flexion of the neck causes the spinal cord to move slightly cephalad

Spinal cord gives rise to 31 pair of spinal nerves( 8 cervical, 12 thoracic, 5 lumbar, 5sacral &1 coccygeal) each composed of ant motor root & post sensory root.

The skin innervated by a given spinal nerve & its corresponding cord segment is called a dermatome.

The spinal nerves & there corresponding cord segments are named for the intervertebral foramen through which they run.

SPINAL CORD cont..

The ant root of the spinal nerve is efferent & motor .

The post root is largely sensory & it conveys fibres of pain,touch,temperature,muscle sensations from the bone,joints & tendons.

Local anesthetic act on the autonomic, motor & sensory fibres, autonomic being most sensitive & motor is least sensitive.

For a given level of sensory block sympathetic block extends 2 segments higher while motor will be 2 segments lower.

DERMATOME

SPINAL CORD cont..

In cervical region the spinal nerve is named after the vertebra forming the caudal half of the intervertebral foramin whereas in the thoracic & lumbar region the nerve root are named for the vertebrae forming the cephalad half of the intervertebral foramin.

Those nerves that extend beyond the end of the spinal cord to the exit site are collectively known as the cauda equina.

the cauda equina consists of vertical lumbar & sacral nerves bathed in CSF that descends to meet their respective foramina.

SPINAL CORD

SPINAL CORD BLOOD SUPPLY There are two posterior spinal arteries arising

from the post inferior cerebellar arteries which supply the post horns & post column of spinal cord.

There is only1ant spinal artery arising from the vertebral artery which supplies the ant & lateral column of the cord.

Many radicular arteries join the ant spinal artery in the cervical & thoracic region.

But radicularis magna ( artery of adamkiewicz) is the only artery supplying the lumbar enlargement.

ANATOMY OF THE SACRUM

The sacral hiatus is of variable shape & size, it’s a inverted ‘V’shaped bony defect covered by post sacrococcygeal ligament.

Sacral canal contains- post portion of the dural sac, filum terminale, sacral nerves, cocccygeal nerves, venous plexuses & fatty tissue.

sacral hiatus is identified by locating the sacral cornua, remnants of the S5 articular processes. This bony defect allows access to the sacral canal.

SACRUM

Sacral hiatus

Sacral cornu

Post sup iliac spine

REFERENCES

BARASH –clinical anesthesia WYLIE & CHURCHHILL DAVIDSONS MILLER LEES SYNOPSIS

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