The spine consists of a series of vertebral segments. The spinal cord itself has neurological segmental levels marked by the spinal roots. A spinal root is named after the vertebra it exits from. When traced back to cord spinal cord segmental levels do not necessarily correspond to the bony vertebral level.
Let us have a look at vertebrrae and nerve root numbers
- Cervical – 7 vertebrae and 8 cervical roots. This discrepancy is because there ar total 8 nerve roots exiting from the cervical vertebrae
- Thoracic 12 vertebrae and 12 roots
- Lumbar – 5 vertebrae and 5 nerve roots
- Sacral – 5 vertebrae and 5 nerve roots
The spinal cord segments are not necessarily situated at the same vertebral levels. This has been caused by difference in vertebral height and height of spinal segment. Thus while first cervical spinal segment is within C1 vertebra, the T12 cord comes to lie at the T8 vertebra.
Similarly the entire lumbar spinal segment lies between T9 and T11 vertebrae and the the sacral cord is between the T12 to L2 vertebrae.
Course of Spinal Roots
C1 spinal root exit the spinal column at the atlanto-occiput junction. C2 root exits at the atlanto-axis. The C3 roots exit between C2 and C3. The C8 root exits between C7 and T1.
The first thoracic root or T1 exits the spinal cord between T1 and T2 vertebral bodies. The T12 root exits the spinal cord between T1 and L1. The L1 root exits the spinal cord between L1 and L2 bodies. The L5 root exits the cord between L1 and S1 bodies.
Relation of Spinal and Vertebral Segments
- First two cervical cord segments roughly match the first two cervical vertebral levels.
- C3 – C8 segments of the spinal cords are situated between C3 through C7 bony vertebral levels.
- Likewise, in the thoracic spinal cord, the first two thoracic cord segments roughly match first two thoracic vertebral levels.
- However, T3 through T12 cord segments are situated between T3 to T8. The lumbar cord segments are situated at the T9 through T11 levels while the sacral segments are situated from T12 to L1. The tip of the spinal cord or conus is situated at L2 vertebral level. Below L2, there is only spinal roots, called the cauda equina.
A rough calculation can be done as follow to obtain a relation between vertebral and segmental level.
- From C2-C6 vertebra add 1 to obtain the spinal segment level
- From T1-T6 vertebra add 2 to obtain the spinal segment level
- From T7-T9 vertebrae add 3 to obtain the spinal segment level
- T10-T12 vertebrae have whole of lumbar segments
- L1 vertebra has sacral & coccygeal segments
- L2 onwards is cauda equina
This has an important beearing in marking the level of injury and correlating with the anatomy. For example if an injury occurs at T10-11 vertebral level, it is going to damage her lower thoracic as well lumber spinal segments.
This also helps to pin point the level of compression.
For all practical purposes whenever lesion in the spine is examined, it is always good to mention injured vertebral and spinal levels sparately.
If they roughly match, the level has been ascertained. if they grossly mismatch somthing might have been missed. There might be another lesion or cord edema.
Popularity: 3% [?]
Related posts:
si je me base sur la relation vertebre-segments,une fracture de la vertebreL1 leserait les segments sacrees et pas les segments lombaires.Sauf que personnellement ,j’ai eu une fracture en L1,et j’ai eu une lesion au niveau du segment L4.Et que ca m’empeche melheureusement de marcher.
y at’il erreur de votre part?
Dr Arun Pal Singh Reply:
February 22nd, 2011 at 6:42 am
This is what Google translated for me from your text
if I look at the relationship vertebra-leg, a fractured vertebra L1 segments would prejudice the sacred and not lombaires.Sauf segments that personally, I had a fracture of L1, and I had a lesion at the segment L4.Et melheureusement that I could not walk.
Are there errors on your part?
Here is answer
No! There are no errors. The extent of vertebral injury and spinal injury may vary. Moreover there are individual variations.
The level correlation is an approximation. It works well but it should not be strictly adhered to like mathematics.
I hope that helps.
Here is the translation
Non! Il n’y a pas d’erreurs. L’étendue de la lésion vertébrale et lésion de la moelle peut varier. En outre il ya des variations individuelles.
La corrélation de niveau est une approximation. Il fonctionne bien, mais il ne devrait pas être strictement respectées, comme les mathématiques.
J’espère que cela
thank you, dr arun! i have been trying to understand the relation of spinal and vertebral level and you made it so much easier !!
may i know which book you referred from?
thank you, dr arun! i have been trying to understand the relation of spinal and vertebral level and you made it so much easier !!
may i know which book you referred from? thanks!
Dr Arun Pal Singh Reply:
August 13th, 2011 at 12:13 pm
@winnie,
Welcome. I do not remember but this is mentioned in many a text books.