Anatomy clinical scenarios (spine)

Question 1

Why can the lateral erector spinae groups no longer extend the spine when the spine is fully flexed?

Answer 1

during spine flexion, lateral portions of erector spinae move anteriorly
in this position, contraction of these muscle groups will produce further flexion of the spine

Question 2

Why do the erector spinae muscles decussate at L4, L5 + S1?

Answer 2

in the lower portion of the spine, posterior support is provided by decussating (crossing-over) tendons of the erector spinae rather than a tough supraspinous ligament
this allows a greater range of flexion in the lower lumbar region as the muscle fibres of erector spinae can relax during flexion

Question 3

What innervates the erector spinae muscles?

Answer 3

dorsal rami of spinal nerves

Question 4

What levels does each dorsal ramus innervate?

Answer 4

innervate muscles at same vertebral level, but also muscles one vertebral level above and below

Question 5

Why is back pain widespread if a small area of erector spinae is damaged?

Answer 5

distribution of sensation in the back makes it difficult to precisely locate the origin of any pain
pain at 1 vertebral level will be transmitted along the dorsal rami of levels above and below too
as brain cannot identify injury location, all 3 sections spasm (to try and protect muscle)
contraction of erector spinae on one side of the spine will pull the vertebral column to that side and so muscles on the opposite side will spasm to pull it back to the upright position

Question 6

Describe cervical vertebrae

Answer 6

small
slender, often bifid spinous process
small transverse process
foramen transversarium present 
no articular facets for ribs

Question 7

Describe thoracic vertebrae

Answer 7

larger than cervical
spinous process = long, projects inferiorly
transverse process = fairly large
no foramen transversarium
articular facets for ribs present

Question 8

Describe lumbar vertebrae

Answer 8

largest
spinous process = short, projects posteriorly
transverse process = large + blunt
no foramen transversarium
no articular facets for ribs

Question 9

What is the function of an intervertebral disc?

Answer 9

hold vertebrae together

absorb shock of forces travelling through them

Question 10

What happens when a disc prolapses?

Answer 10

weakness in annulus fibrosus allows jelly-like nucleus pulposus to be pushed out from centre of disc

Question 11

Why do we refer to the muscles posterior to the spine collectively the erector spinae muscle mass?

Answer 11

can split into names groups, but the erector spinae consists of 100s of individual muscle fibres

Question 12

What are and what is the action of the long erector spinae muscles?

Answer 12

iliocostalis, longissimus, spinalis

extend + laterally flex spine

Question 13

What are and what is the action of the smaller erector spinae muscles?

Answer 13

semispinalis, rotatores, multifidus

rotate spine

Question 14

Why can a small area of damage in the erector spinae muscle mass cause such a big pain effect?

Answer 14

lots of cross over between nerve supply of adjacent vertebral levels
difficult to precisely locate origin of any injury + response may be disproportionate to extent of injury

Question 15

How does the inflammatory response affect the muscle fibres?

Answer 15

can go into spasm + become locked

Question 16

Why can damage to one side of the erector spinae muscles cause muscles on the other side to go into spasm?

Answer 16

spasm of one side of the spine will result in lateral flexion of the vertebral column, so muscles on the other side also go into spasm to keep the back upright

Question 17

What structures can be compromised by a herniated disc?

Answer 17

posterior prolapse = spinal nerves or spinal cord itself can be compressed

Question 18

Which movement do the majority of the spinal ligaments limit?

Answer 18

flexion of spine

Question 19

To touch our toes, we have a greater ability to flex the spine between the L4, L5 and S1 vertebrae. What structure replaces the ligaments at this level?

Answer 19

decussating tendons of erector spinae muscles

Question 20

What is the disadvantage of having increased range of movement in lumbosacral region?

Answer 20

greater range of motion can put more strain on vertebrae + discs in between them and therefore prolapsed discs most commonly occur in this region

Question 21

Why does the spinal cord become wider in the cervical and lumbar regions?

Answer 21

increased density of nerve fibres enter and exit spinal cord at these locations as brachial + lumbar plexuses of limbs lie at these levels

Question 22

What type of information is carried by the dorsal rootlets?

Answer 22

sensory fibres

Question 23

What type of information is carried by the ventral rootlets?

Answer 23

motor fibres

Question 24

What structures are innervated by the dorsal rami?

Answer 24

muscles + skin of back (erector spinae)

Question 25

Cerebrospinal fluid function

Answer 25

protect + nourish spinal cord

Question 26

Between which meningeal layers is CSF found?

Answer 26

between arachnoid mater + pia mater (sub-arachnoid space)

Question 27

Why are samples of CSF taken below the level of L1?

Answer 27

increased range of flexion at this level = larger spaces between vertebrae and therefore easier to pass between them + pierce dura mater
spinal column stops at L1 in adults and below continues as bundle of spinal nerves (cauda equina) - if needle enters level of cauda equina, spinal nerves can be pushed out of the way, decreasing risk of nerve damage

Question 28

What are the 3 meningeal layers?

Answer 28

dura mater
arachnoid mater
pia mater

Question 29

Why does a lumbar puncture need to be below L3 in children?

Answer 29

in early development, spinal cord + vertebral column are same length
during growth of body, body can grow more quickly than spinal cord
as we age, spinal cord ends up (relatively speaking) shorter and shorter ending at around L1 in adults
process is ongoing in children and therefore spinal cord finishes at lower level, around L3