Thoracolumbar junction is the junction between the Thoracic spine and the Lumbar spine. The junction consists of the part of the vertebral column from the eleventh thoracic vertebra to the first lumbar vertebra. Here the spinal curvature changes from kyphosis to lordosis, and the orientation of the facet joints changes from coronal to sagittal. 12th thoracic vertebra to 2nd lumbar vertebra.
The thoracic spine contains 12 vertebrae and lumbar spine 5. The change in vertebral anatomy adapting to lumbar anatomy can be noticed in last two thoracic vertebrae.
Thoracolumbar junction is important because it marks the change of region. To identify different junctional vertebrae different counting methods are applied.
A thoracolumbar transitional vertebra or tltv is defined as a vertebra with partially retained features of the thoracic and lumbar segments at the thoracolumbar junction.
For example there may be 13 thoracic and 4 lumbar vertebrae.
TLTV also makes necessary to count the vertebrae in right manner
The issue of counting arises on the images. For certainty, either the image of whole spine should be available or thoracic and lumbar vertebra should be identifiable by marked landmarks in the given image. SO it is important to identify correct vertebral levels in thoraco-lumbar x-ray by just looking at that x-ray, to avoid cost ineffective whole spine imaging.
Different Methods of Vertebral Counting in Thoracolumbar Junction
Counting Down from C2 or T1
This method is commonly used.
The last thoracic vertebra is defined by counting down from the second cervical vertebra (C2) or the first thoracic vertebra (T1) under the assumption that there are 12 thoracic vertebra.
The cervical spine has a relatively stable morphology and a fixed vertebral count of seven.
But, the number and distribution of thoracic and lumbar segments exhibit considerable variation,[ There could be 22, 23 or 25 presacral segments, there could be 13 rib bearing thoracic vertebra with 4 lumbar-type vertebra or 11 rib-bearing thoracic vertebra with 6 lumbar-type vertebra.
By Identification of Ribs
By labelling the rib-bearing vertebra as the thoracic vertebra, one does not need whole spine images and allows segmentation of the lumbar and thoracic vertebra. But there is lack of definite criteria by which ribs can be differentiated from rib equivalents.
Differentiating Thoracolumbar Transistional Vertebrae
Differentiation of vertebral segments at the thoracolumbar junction as the TLTV or non-TLTV (thoracic or lumbar) segments through definitive criteria for differentiating the most caudal ribs also enable surgeon to identify without whole spine images.
An axial image that shows the relationship between the vertebra and most caudal ribs is required for it.
Types of Caudal Ribs
Two of the counting methods and classification of TLTV involves identification of caudal ribs.
A rib articulates with the facet at the body or pedicle of the vertebra.
Most caudal ribs can be classified into one of four types
- Normal rib – >3.8 cm length rib
- Hypoplastic rib (short rib)- A separated bone <3.8 cm
- Unfused transverse process (accessory ossification centre or lumbar rib) – A structure articulating with a shortened lumbar costal process or as a structure that was linearly adjacent to such processes
- Mixed type – Does not not meet any of above criteria. it appears as a separated bone articulating with the facet on both the pedicle and transverse process.
Thoracolumbar transitional vertebra
A thoracic vertebra is identified by the presence of paired ribs that are 3.8 cm or more in length and originate from the facet at the pedicle (or the body of the vertebra). By contrast, a lumbar vertebra is defined as a vertebra without articulating ribs, the absence of facets for a rib on the pedicle (or the body of the vertebra), with fused transverse processes.
A transitional vertebra is defined as one with characteristics of the corresponding superior and inferior segments, whereas the TLTV is defined as a vertebra with partially retained features of the thoracic and lumbar segments at the thoracolumbar junction.
Five types according to the length of the separated bones, the presence or absence of a facet at the pedicle (or body) of the vertebra and the presence or absence of articulation with separated bones.
iIncludes paired ribs with more than one short rib
A 3.8-cm or longer rib on one side and an accessory ossification centre or transverse process on the contralateral side
Short rib on one side and an accessory ossification centre or transverse process on the contralateral side
Unilateral or bilateral mixed type rib
Unilateral or bilateral accessory ossification centre.
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