Lumbar Spine Anatomy - What Causes A Slipped Disc? - Dr Gill

[Music] [Music] hello and welcome back to the channel you join myself Dr James kill for a new clinical skills adjacent video today we're going to be looking at the lumber spine looks like a lollipop but I assure you it's not the reason why I thought this would be a good idea to go over is that when it comes to low back pain it's actually the vast majority of the time we're talking about issues from the lumber spine so I thought it worthwhile to discuss the anatomy of the lumber spine but also pay attention to that very common source of back pain sciatica and perhaps explain what goes on here with regard to the Diss and how that causes pain because it's really useful to be able to explain to a patient what's actually going on when they come in and say they've got a slip disc because as you'll see I'm not a fan of that as a description because the disc doesn't so much slip as it pops but we'll have a look at that when we get into the vertebral Anatomy so when we're talking about the lumber spine broadly we're talking about seven structures we've got the bottom five vertebrae that's L1 to five the intervertebral discs themselves the spinal cord running down the length the nerve Roots when they're coming out and the ligaments and muscles that hold the whole thing together and finally the blood vessels which often you don't see on these sorts of models which keep everything fueled and oxygenated so first off let's look at the vertebrae realistically when these are all stacked together they form the vertebral column or spiners often people describe it but we're going to discuss the lumber spine as it gives a clearer picture to what's going on now in biology form will follow function and we can very much see that with the vertebral bodies because the spine Bears 80% of a person's weight and the lumber vertebrae have grown in size to compensate for this this is particularly noticeable with these hockey puck shaped pieces of bone on the front of the vertebrae the vertebral bodies now interestingly or at least it is me the vertebral body is comprised of two different forms of bone structure which you can see on the model here we've got a dense cortical shell on the outside this is required to ensure we've got even Force distribution across the vertual body this is a very stiff bone and it means the the body is able or the spine is able to Bear those compressive loads of walking running and jumping basically life without buckling but then form falling function the cortical shell encases a second bone type this is the spongy tracular bone the tracular bone as you can see here is quite different in appearance it it it looks spongy and that's critical to the absorption of forces which is the main or one of the main roles of uh this bone see it's all well good having this strong cortical bone that can withstand those axial forces without damage but the latis work structure of the um tacular bone here actually helps absorb those forces and efficieny transfer to the cortical bone to allow Dynamic movement for want of a better phrase you don't want the force going in and then passing through the force of leas resistance that's how you end up with fractures now interesting enough the bones of the spine aren't inert structures this spongy tracular bone is actually filled with a very active metabolic tissue red marrow and that's crucial because it plays a role in production of red blood cells also termed hematop pois which is a a lovely chewy word um the vertual bodies though they play an important role as well in Mineral and storage particularly calcium and phosphate but that's a little bit more than we're dealing with today taking away that metabolic side obviously the main role of the spine is that of support and movement and both realistically are made possible because of these intervertebral discs sat on top and below the vertebral bodies now the movement is further facilitated by something called Highline cartilage which is a layer that sits on the top and the bottom Superior and inferior aspects of the vertebral body now bear with me for a second I've always frankly viewed the layup of the vertebral bodies in the spine with the uh discs it's a little bit like a cucumber sandwich you've got the two bodies on top they're covered in this buttery Highline cartilage and a thick slice of cucumber in between now keep that idea of a cucumber sandwich in mind as I do think it helps understand the problems with the discs which we're going to come to shortly but let's leave our cucumber sandwich for moment and go back to the Bony Anatomy let's move posteriorly from the vertebral body and then we come to the vertebral Arch which is sort of the back bit here with all these spiky bits coming off now the crucial thing here is how the vertebral body and the arch together form a central hole the um vertial Forin now when the vertebra viers are collective the whole spine these foren will line up to give us the spinal canal or the vertebral Canal as it's sometimes called Okay so we've covered the vertebral body we talk we've talked about the arch now let's cover these spiky bits at the back of the vertebrae starting most posteriorly this is the spinus process and it's the bit that's most prominent that knobbly bit when that you can feel in the middle of your back when you press your spine the main function of this spinus process is as an attachment point for muscles which allow for extension and rotation as well as stabilization in the spine it's also the site of ligaments that help the vertebral column maintain stability okay so that's the spinus process then connecting in we've got these small sers of bone called the lamina these form the posterior walls of the vertebral Arch and largely part of the spinal canal does seem like a simple straightforward Junction between the spinus processes and the transverse processes which is reasonable however there is another piece of tissue called the ligament and flavum and crucially that attaches here it's this big fiber elastic band that stretches all along the posterior wall of the vertical canal and it helps both stabilize and prevent excess movement of the spine but it has what I think is a very cool function that because it's very elastic nature this ligament INF flavor also helps return the spine to the neutral position once you've you know been bending forwards and backwards and things so in doing so we're focusing on that elastic response of the ligament and flavor so we're not putting excess strain on the other structures and there's probably an element to be said about energy saving but I don't know that one for a fact so now we're going to come to the wings of the vertebrae these are the transverse processes and they come out laterally these are areas of you know large areas of muscle insertion and they act as levers with regard to helping for flexion extension and twisting motions and this is tend to be through muscle groups like The erectus Spina a quadratus lorum and the other deep spinal muscles very much like the vertebral Arch protecting the spinal cord the transverse processes also act to Shield some of the nervous system specifically the nerve roots and the blood vessels of the spine if we come more superiorly though we've got a um the superior articular processes arising just before transverse processes now these form facet joints down uh the spine and again they help with aiding movement as they prevent excess movement and add to the stability of the lumber spine finally at the bottom part we've got the pedicles which are going to connect the vertebral body and the arch together in conert with the pedicles the superior and inferior processes do create Forin through which the nerve Roots will um exit now that's very very crucial because although we've wrapped up the Bony parts of the spine that exit part of the nerve root is going to play a crucial part in issues with sciatica so let's look at some of those softer Parts particularly the nerve Roots as you said the the lumber nerve Roots exit through the Forin on each side of the vertebrae these are part of the peripheral nervous system and expend from the spinal cord out to the nerve uh that are supplying the legs pelvis and lower abdomen all sounds pretty straight forward until there's a problem which as I've mentioned several times now is often not always but often due to the intervertebral discs the intervertebral discs are these fibrocartilages structures situated between the vertebral bodies now if I go back to my cucumber analogy if we think we've got that tough GRE green outer skin and inside a more lighter jelly like Center the same is true for the invertable discs there's something called the anulus fibrosis a tough fibrous ring of type one collagen that's on the outside and to be honest you can kind of see that biology certainly the naming is very straightforward it does what it says on the tin anilus being ring and fibrosis being fibrous so what when we're talking about the anulus fibrosis we're talking about a tough fibrous ring which going back to the cucumber is on the outside then we need to deal with the squidy bit inside that's the nucleus pulposis this gel-like Center provides flexibility and shock absorption within the spine so very much like the Cucumber the anulus fibrosis that thick fibrous tissue on the outside keeps the nucleus pulposis in place and allows the pulposis to compress and absorb without moving out of position and that's the crucial bit here now it's very important to understand this structure and highlight why the concept of the slip disc as mentioned isn't actually accurate so there's something called radiculopathy when the disc slips no when the disc herniates I'm sorry I can't stay with slip disc it herniates and then we get nerve compression because of the herniated intervertebral disc pressing on the nerve now as I mentioned really early on the disc hasn't slipped it's actually popped now that technical term for that is herniation given that the definition of a herniation is an abnormal tissue protrusion through an opening that can occur anywhere in the body when I was little I had an inguinal hernia part of my bowel the abnormal TI isue protruded through an opening a defect in my abdominal wall and I got this extra bolt coming out hernas are possible anywhere you've got basically a wall and a tissue or an organ on the other side hopefully put that one clearly so nucleus pulposis bursts through the anulus fibrosis and doing so you end up with a bulge and that's often putting pressure either on on the nerve root or the spinal cord now realistically the most common direction of herniation of a dis is posterior laty hence very commonly we get sciatica because it's the nerve root that's being compressed rather than spinal cord itself however the spinal cord can still be compressed and then we've got a world of problems and that comes into a medical emergency and if we herniate even lower down the lumbar spine then because the cord has no longer stayed as a cordlike structure at that point it's become the um cord quina this again Latin horse's tail looks like a horse's tail hanging down rather than a single cord if you get a herniation pressing on the Cordina then you can get massive problems in terms of what's called cordin syndrome where you lose function of the bladder and bowel your legs and hence why somebody coming with sciatica I need to be able to show that there's no evidence of Cordina these are Big level problems so either Cordina compression nerve root compression whatever it is if we've got the disc herniated and pressing on something the definitive treatment is trimming of that herniation to hopefully remve the pressure and then that'll hopefully allow the nerve to recover that word hopefully is doing an awful lot of lifting but perhaps we'll do another video on you know um the specifics of nerve root compression and spinal core compression at another point but putting that to a sight we'll go for a small diversion into health and safety material the reason being is you're going to see all these comments when you do health and safety stuff about bending from your knees and not your back the reason being is when you bend forward you put the greatest amount of pressure on the front of the intervertebral discs which is fine you know we've got that anulus fibrosis protecting the nucleus pulposis so we can withstand that pressure however when you pick something up using your in your arms just using your back you using your spine as a lever these forces are massively magnified that does increase the risk of muscle damage but it seriously increases the pressure on the nucleus pulposis which if we've got all the pressure at the front very little on the back there's a greater likelihood of the anulus fibrosis failing and the nucleus pulsus pushing backwards that rupture obviously is going to end up with a compression of some form again hopefully you can see the wire slip disc is a poor view of describing these injuries so we said the main function of the intervertebral disc is to facilitate movement I'm going going to go right back to my cucumber sandwich analogy if you try rubbing two pieces of bread together everything's going to fall apart now if you butter them that movement might get a little bit easier realistically it actually gets stickier but stay with my analogy however if you then put some cucumber between that butter and the bread you're suddenly going to get much less friction and much more movement this is the purpose of the discs the the fibrocartilagenous cartilage works with the Highline cartilage on the vertebral bodies to enable that smooth turning movement and flexibility of the spine which is one of the reasons why these tissues can also end up with simple wear and tear as we age because whilst they're reducing friction that constant movement and pressures that they're under will over time lead to degener ation and that's not in terms of causing um herniations that's just straightforward pain and reduced Mobility but as the whole system is wearing out it's also going to increase the risk of herniation so basically if you have back pain make sure that you're doing proper lifting techniques Because unless you've had amri scans and things like that you don't know exactly where that pain is coming from so assume that you just got a little bit of wear and tear and therefore the probability of a herniation if you put too much force through your back um is increased I think you can see that I honestly think the intervertebral discs are the most interesting part of uh the spine I mean it doesn't only allow that movement but all the compression and shock absorbing you know think about what you're able to do in terms of running and jumping rolling you know and your spine just says yeah and it takes it and we've said before we've got a huge amount of shock absorb coming from the tracular bone but it's nothing compared to the shock absorption from the intervertebral discs any patient that's had a lumber disectomy will tell you that they feel like some of the Bounce has been taken out of them because they can't well absorb those same shocks well I think this is probably a good place to leave things today we've discussed the anatomy of the lumbus spine we've commented on the various bony prominences throughout the vertebrae and outlin the function and issues that can uh Bea the intervertebral discs so I hope this has been useful for yourselves and I've not wax lyrical about the discs too much as opposed to any other parts of the anatomy but if it has been useful please give the video a like and um you know put a comment down below that um you know might guide us to how um going to produce other videos I know this one had been requested for a while um with that mine take care Ander I'll see you in the next one Che