 Good day everybody. This is Dr. Sanjay Sanyal, Professor Department Chair. I'm holding up an articulated vertebral skeleton in front of you and I'm going to demonstrate a few special features about thoracic vertebra and the lumbar vertebra with some clinical significance. Now I'm holding the entry portion so that you can see the front part and you can see that this is the thoracic region with the intervertebral discs. The thoracic vertebrae has got very limited almost no movement and whatever limited movement which takes place it takes place in a small rotary axis and that imaginary axis passes through the center of the vertebral bodies. You will see the posterior aspect. So let's take a quick look at the thoracic vertebra especially the T12. So let me just quickly count them out for you. This is tibra prominence. This is C7. So this is T1, T2, T3, T4, T5, 6, 7, 8, 9, 10, 11, 12. If you take a look at the 12th thoracic vertebra closely and I'm going to turn it you will find that we can see the articular facets. The superior articular facet is here and the inferior articular facet is below. To a thoracic vertebra superiorly it has to articulate with T11 below it has to articulate with L1. So superiorly the thoracic articulations are more in a coronal blade therefore the superior articular facet of T12 is in a coronal blade because it has to articulate with T11. The inferior articular facet is located in a sagittal axis because the inferior facet has to articulate with L1. Lumber vertebrae they are capable of forward backward movement and therefore the articular facets are in a sagittal blade. The thoracic vertebra as I mentioned has got only a slight rodentry movement and therefore the articular facets are more in a coronal blade. In order to understand this concept of the articular facets what we have done now is we have shown the same thing from a different perspective. We have kept a few individual thoracic vertebrae in a sequence. So take a look at the first few thoracic vertebrae you notice that the articular facets are pointing in a coronal blade because they have to allow for a slight rotatory movement and we have kept the upper thoracic vertebrae in one plane and now I'm going to show you the middle thoracic vertebrae in a sideways view and we can see the same thing. We notice that the superior articular facet and this is the inferior articular facet. They are all located in a coronal blade. Let's come lower down we see the same thing we see the thoracic vertebrae, the superior articular facet, the inferior articular facet. They're all in a coronal blade and finally let's come to the 12th thoracic vertebrae and here we shall see something very unique and I would want you to watch very carefully. This is 12th thoracic vertebra superior articular facet and you notice that this is in a coronal blade while the inferior one, this is the inferior one, this is located in parastrojetal blade and why is it so? Because this has to articulate with L1 and that brings me to the L1 vertebra itself which I have shown here. The L1 vertebrae they allow flexion extension so that for all the articular facet superior and inferior they are located in a parastrojetal axis and we can see that here and we can see some more the lateral view we can see that the superior articular facet and the inferior articular facet they are all located in a parastrojetal axis so therefore the T12 vertebra is the transition between T11 above and the L1 below so therefore the superior articular facet is coronal and the inferior articular facet is parastrojetal so therefore T12 is the so-called atypical 12th thoracic vertebra. So therefore T12 vertebra is subjected to maximum stresses and strains during daily activity. Now let's come a lower down we take a look at the L5 vertebrae and if you look very closely L5 vertebra articulates with S1 therefore we can see this is the superior articular facet and this is the inferior articular facet. The superior articular facet articulates with L4 the inferior one articulates with S1. The small space in between the two that is referred to as the powers interarticular is. Now I shall demonstrate the same concept to you from a different perspective. Now we are focusing on the Lamos sacred region for the posterior aspect and just to bring up the speed this is the L5 vertebra seen from the posterior aspect the spinous process and we can see it's articulating with the S1 here. So take a close look at what I'm pointing this is the superior articular facet of L5 which is articulating with the inferior articular facet of L4 and this is the inferior articular facet of L5 articulating with the superior articular facet of the first piece of the sacrum and that is the same thing you know the other side. So therefore this is the inferior this is the superior so therefore this junction the small portion is referred to as the powers interarticular is. In degenerative weren't there this interarticular is it stretches the so-called Scotty Dog sign seen on oblique lateral x-rays and that is referred to as lumbar spondylolisis. So when it happens on both the sides then what happens basically is the whole vertebral lamina and the arch it gets disengaged from the superior articular facet and it remains stuck to the S1 the rest of the lumbar vertebra along with the upper vertebral column it gets disengaged and it moves forward and that is referred to as lumbar spondylolisis. L5 vertebra and the rest of the vertebral moves forward on S1 that happens if there's a bilateral lumbar spondylolisis that is called spondylolisthesis. This is a posterior lateral oblique x-ray of the lumbar spine to show how the posterior elements of the lumbar spine form the Scotty Dog and this is a posterior lateral oblique x-ray to show how the neck of the Scotty Dog seems stretched in case of spondylolisis and this is a CT scan of the fifth lumbar vertebra to show bilateral spondylolisis which is a break in the powers interarticular is and this is a lumbar spinal MRI to show spondylolisthesis. The next thing I will draw your attention to is this structure that we can see here this is a representation of a herniated nucleus pulposus. Nucleus pulposus usually herniates in the lower lumbar or the lower cervical region so here they have shown a lower lumbar nucleus pulposus herniating. This happens when there is a sudden flexion of the lumbar spine or the cervical spine in an unguarded situation. Annihilus fibrosis ruptures and nucleus pulposus herniates out. It usually herniates in a posterior lateral direction because the posterior is guarded by the posterior longitudinal ligament. When it herniates it presses on the emerging spinal nerve. It presses on the spinal nerve with a higher numerical value so if L4, L5 just herniates it presses on the L5 spinal nerve and therefore L5 is responsible for dorsiflexion, S1 is responsible for plant flexion. So this is just a quick rule of thumb. So that is about the herniation of the nucleus pulposus. This is an MRI of the cervical spine to show herniation of the nucleus pulposus pressing on the extraneous space and this is an MRI of the lumbar spine to show herniation of the nucleus pulposus. These are few points I want to mention about the thoracic lumbar spondanolysis, dysthesis and herniation of the nucleus pulposus. Thank you very much for watching. Dr. Sanjay Sanyal signing out. If you have any questions or comments, please put them in the comment section below. Have a nice day.