The Lumbar Spine
Let’s talk about the humble lumbar spine (L-spine). This is the lowest part of the spine. It is below the cervical and thoracic regions. The lumbar spine consists of 5 vertebrae and they are numbered sequentially from the top down, L1 vertebrae, L2 vertebrae… L5 vertebrae. The L5 vertebrae sits on top of the sacrum. The first sacral vertebrae is called the S1 vertebrae. Whereas the L1 vertebrae sits below the T12, 12th thoracic vertebrae.
There are many specific features that make the lumbar spine unique from the other parts of the spine. Let’s start with the vertebrae themselves. Looking at the vertebrae, the first thing that people notice is the size of the vertebral body, it is much larger than other vertebrae. When someone stands up or sits, approximately half their body weight is above the L2 level, our center of mass. This means that the lumbar vertebrae can take a great amount of pressure and loading. The vertebral body is built a little different to
allow this amount of weight to pass through without causing injury. The outside of the vertebral body is cortical bone. This type of bone is very hard and strong. However it is also brittle. If the vertebral body was hollow and made of cortical bone it would be similar to a cardboard box. The vertebrae would be able to withstand a lot of force but once that force capacity is reached, it would fold in, on itself, like a cardboard box. To stop that from happening, the vertebral body has cancellous bone inside. This cancellous bone is a softer, spongier bone that helps to absorb the load on the vertebrae. The cancellous bone is just not put in there perfectly matching the outside dimensions of the vertebrae. The cancellous bone is in the form of trabeculae. Trabeculae are lines of bone that help to transmit the forces. There are vertical and horizontal trabeculae. The vertical trabeculae help to stabilize the ‘cardboard box’ of cortical bone to vertical forces. However, if there is a vertical load and a horizontal force, for example lifting and twisting, the vertebrae can collapse. This is where the horizontal trabeculae come into play. Both the vertical and the horizontal trabeculae act as a stabilizing grid with in the cortical bone vertebral body to give it amazing compressive strength as well as strength with forces shearing across the body as well. The body is built so amazingly well.
Coming off the back/posterior aspect of the vertebral body, are the pedicles. There are two pedicles. The pedicles are short and stout, it is not very common to break a pedicle. The pedicles travel posteriorly for about 1 cm or so, then they slowly start to angle towards each other and they meet in the middle. Where the pedicles angle, the name changes as well, they are now called lamina. The lamina meet in the middle and form the spinous process. The pedicles come out of the vertebral body about ⅓ of the way down. Something else happens where the pedicles turn into the lamina. There are 3 other bony parts that emerge. The superior articular facet, the inferior articular facet and the transverse process. These three bony growths occur on both, the left and right sides of the pedicle/lamina intersection.
Let’s discuss these three bony prominences. The superior articular facet attaches to the inferior articular facet of the vertebrae above. They are complementary, that is the superior facet faces anterior, superior and slightly lateral. While the inferior facet faces, posterior, inferior and slightly medial. The facet joints, more commonly known as zygophopheal joints, or z joints, are one the main factors that controls the motion of the lumbar spine. The orientation of the z joint facets is something that is different than anywhere else in the spine. The z joints in the cervical spine, neck, are planar joints, on average at about 45° above the horizontal plane. While the z joints in the thoracic spine, mid back, are quite planar as well but this time in the coronal place, close to being straight up and down. However, the z joints in the lumbar spine are different.
They can be either ‘J’ or ‘C’ shaped. This may get a little complicated in the next few lines… The ‘J’ shaped joints are mainly in the sagittal plane, front to back, with the little hook being in the anterior part of the joint in the coronal plane, side to side.
The ‘C’ shaped joints tend to fit in the middle of the sagittal (side-to-side) and coronal (front-to-back) planes. Looking down from the top, the joint looks to be in a ‘C’ shape.
To make things even more complicated, the z joint shapes may be different side-to-side of the same vertebrae! This is called tropism. A tropism can really muck things up when trying to help someone with a stiff low back. You are trying to mobilize/ manipulate the z joints in the lumbar spine but they always feel stiff, that could be because the plane of the joints, the imaginary line that passes through the joint that separates the front and back halves of the joint, can be different from the joint above and the joint below. Tropisms are diagnosed via MRI or CT scans. The finds of the scan are listed with side note, “…the left L3-4 facet is a tropism compared to the rest of the z joints in the lumbar spine…”. Tropisms rarely cause issues, they are just found and help to explain things.
Now where were we… oh yes, the facet joints. Only one more thing left to say about the facet joints. It is the little piece of bone between the facets on the same vertebrae, the pars interarticularis. This little piece of bone has to be strong. The pars is mainly made out of cortical bone, see above. When people are flexible, not quite Cirque du Soleil flexible, and they bend backwards a lot, the inferior aspect of the superior facet can come crashing down on this point, pars interarticularis. If this happens repeated number of times in a short period or a fairly consistent number of times over a longer period, this part of the bone can start to break down and people can have a stress fracture here! This is spondylolysis (big word of the blog). It means just that, breaking of the bone, specifically the pars interarticularis. This can have some pretty dramatic effects over time. One example, is that the vertebrae with the fracture MAY start to slip forward over time and cause what is called a spondylolisthesis. A couple of the bad things with a spondylolisthesis is that the spinal canal can get quite a bit smaller and this can lead to possibly needing spinal surgery in the future.
Let’s stop about something more pleasant than spinal surgery, shall we? The other bony point that sticks out from that point is the transverse process. The transverse process sticks out of the side of the vertebrae. It is slightly tilted backwards from the coronal plane. The transverse process is thought to act as a lever to move the vertebrae. The muscles that attach to the transverse process are psoas and quadratus lumborum, to name a couple. In addition, there are multiple ligaments that attach to the transverse processes, think of them as “guy wires” that help to stabilize the lower lumbar vertebrae by attaching them to the other vertebrae and the pelvis.
Leaving the pedicle/ lamina intersection, heading posteriorly, backwards, we go along the lamina. Both laminae head towards the midline and attach. This is a very important attachment. This attachment of the lamina closes the circle around the spinal cord, creating the spinal canal or spinal foramen in the lumbar vertebrae. This bony arch protects the spinal cord from injury and provides a very stable surface for the spinous process to attach to. If an
injury does occur, or sometimes simply with aging, the lamina start to get thicker. This can cause the spinal canal to get smaller, creating what is called spinal stenosis. People with spinal stenosis tend to dislike extension, for example, standing up straight. They find that standing up straight may hurt their back, send pain down their legs or make their legs feel very weak. Or all of the above! Generally people with spinal stenosis like to be slightly bent forward, in a little bit of flexion. For example, they cannot stand up straight and walk around to go grocery shopping. However, if they get a shopping cart and are able to lean on the handles, they can walk around 2 or 3 large grocery stores or a shopping mall, without any issues! If someone gets severe spinal stenosis, you may end up going and getting a laminectomy from a neurosurgeon. The basics of the surgery is that the neurosurgeon snips off the lamina, just behind where the facet joints/ transverse process are located, on both sides. This, in theory, opens up the spinal canal so there is less pressure on the spinal cord/ nerves. The lamina and the spinous process are then removed and the client is beautifully sewed up. My experience working with people that have had a laminectomy, at least the first few days after surgery, is that most of them do quite well. There is still pain, after all they just had surgery, but their pain has changed, they can stand up straight, there is less leg pain, they can walk further… However all is not always good. Even though it is a routine surgery, some people still pass away during or after the surgery. There is an inherent risk of simply having surgery. It should be the last opinion.
Lastly, on the vertebrae, but definitely not least, is the spinous process. The spinous process is short and stout. The lumbar spinous process has a single tip that points straight back. Unlike the thoracic vertebrae, whose spinous process points inferior and is usually level with the vertebrae below or cervical spinous process is usually bifid, two tips. Like the transverse process, the spinal process is a long lever off the vertebrae to control the motion of the vertebrae. Some muscles attach to the spinous process. In addition, more commonly ligaments attach to here, for example, the interspinous ligament, supraspinous ligament and the thoracolumbar fascia. These ligaments all play a role to limiting the movement of the vertebrae. The L5 spinous process is one of the shortest and a little more difficult feel for when palpating the vertebrae on a client. A simple trick to make sure you are on the L5 spinous process is the find the clients PSIS, posterior superior iliac spine, go to the middle between them and that should be the S2 level, go up superiorly about 1 cm, that is S1 and go superior again 1-2 cm. That should be the L5 vertebrae, to make sure ask the person to tilt their pelvis a little bit. The L5 spinous process should disappear under your fingers.
That is a simple walk around the lower vertebrae in the L-spine. Let’s move on to the next important piece of that area of the spine. The lumbar disc…
Lumbar discs sit between the vertebrae and are named for the vertebrae above. For example, the disc sitting between the L1-L2 vertebrae is considered the L1 disc. The discs are the largest in the body as they absorb and transfer a lot of forces from one vertebrae to the next. Lumbar discs actually grow throughout your life! Yes that is correct,it is normal for them to grow. The discs are usually 1-2 mm taller at age 60, than they are at age 20. Most people are very surprised to learn that, it has been a common thought pattern that lumbar disc shrink and degenerate but that is not the reality of the situation. The disc seems to be the perfect object to sit between two vertebrae. Not only does it permit 360° of movement but it also helps to absorb and transmit loads from one vertebrae to another. The lumbar disc is made up of two components: the annulus fibrosus and the nucleus pulposus.
The annulus fibrosus, or the annulus, is the outer component of the disc. The annulus is composed of 60-70% water. The annulus slowly dehydrates throughout our lifetime. Type 1 collagen primarily makes up the annulus. That type of collagen is strongest under tension, being pulled. The annulus is made out of 10-20 concentric rings of collagen. The collagen fibres, in the rings, are orientated about 65° from the vertical. Each ring is orientated in the opposite direction. For example, the first ring is orientated to the right, the next is to the left, the next is to the right… The orientation of the rings, that 65° number, is nearly the perfect orientation to give maximum support to protect against rotation. There is only one problem, only half the disc resists rotation at one time. If I rotate to the left, half the disc, the rings orientated to the left, take up the tension, become taut and limit my rotation. However, the other half of the ring, orientated to the right, become slack. The rings or laminae of the disc, are thickest in the front and sides of the disc. The laminae are the thinnest in the posterior and posterolateral corners, this is where disc herniations occur most commonly. In addition, upto 50% of the disc rings in the posterior lateral corners are incomplete. That area is the weak link in the chain for tearing the annulus fibres. The outer rings of the annulus are considered a ligament that helps to limit movement in the lumbar spine. The outer laminae have nerve supply and a blood supply. This means that if you tear the outer annulus, it will hurt. However, the tear can heal because of the blood supply! People that think that a disc tear/bulge last for ever, are incorrect. Thank goodness!
The nucleus pulposus, aka nucleus, is the center area of the disc. The nucleus is made up of Type 2 collagen. That type of collagen differs from Type 1 collagen. Type 2 collagen has a higher compressive strength. Just like the annulus, the nucleus is made up of water, 90% when we are younger and dehydrates to about 70% later in life. The nucleus does not have any nerve innervation and it has no blood supply. So how does it survive? Everything needs blood and oxygen to survive in the body. The secret to allowing the nucleus to survive, we think, is the vertebral end plate. The vertebral end plate is the top and bottom of the vertebral body. It is made out of cartilage, hyaline and fibrocartilage, in young people. When you get to my age, it is mostly fibrocartilage. The functions of the vertebral end plate are to attach the disc to the vertebrae, it is a zone of growth and diffusion of nutrition to the disc/ nucleus. Being a growth zone, the end plate would have a lot of blood supply. The oxygen would diffuse across from the end plate to the disc/nucleus. Compression and transmitting loads would create a pump like system to push fluid across the cartilage and the unloading of the end plate would create a sponge like effect to pull the waste away from the center of the disc. It is so neat how it all works.
Let’s have a brief example of how the discs and the end-plates work together to transmit loads. When there is weight put on the spine, the pressure increases in the nucleus which pushes it outwards, in all directions into the annulus. The annulus then tightens up and this force is exerted back onto the nucleus to stop it from expanding. The
pressure is then exerted onto the vertebral end plates. The end plates then transmit the load through the vertebrae and onto the next vertebrae. You read it and it seems to take 10-15 seconds. In reality, it occurs in a fraction of a second. This is not without risk though. If the load comes on too fast or too much load is bore on the vertebrae, the vertebral end plate may fracture. The vertebral end plate is the weakest part in the transmission of forces. If there is a vertebral end plate fracture, the disc might migrate into the body of the lumbar vertebrae. This creates what is called a Schmorl’s node. These nodes can be seen on x-rays or other diagnostic imaging. There is a thought that if caught soon enough, with diagnostic imaging, that degenerative discs in the lumbar spine all start with end plate fractures and Schmorl’s nodes can be seen. Very interesting, indeed!
So we know that there are two vertebrae and a disc hold the vertebrae together. What else helps to support the spinal column? Ligaments, of course. Ligaments are bands of type 1 collagen that attach from bone-to-bone. They are like little pieces of rope, the do not contract like muscles, they only hold everything in place. Let’s chat about all the different ligaments in the lumbar spine, where they are, what they do and how the help to protect the spine.
The anterior longitudinal ligament, ALL, runs down the anterior aspect of the vertebral bodies. The ALL helps to limit movement when the spine bends backwards, goes into extension. It also helps to limit anterior and posterior translation, frontwards and backwards sliding of the vertebrae on one another. The ALL has many different layers of fibres. The short fibres go from one vertebrae to the next, while the long fibres can span up to 5 vertebrae. The ALL is loosely attached to the anterior aspect of the annulus and the rims of the vertebral body. Between the ALL and the vertebral body are where the nerves and blood vessels to the vertebral body are kept.
The annulus fibrosis. As mentioned above, the annulus is outer aspect of the disc. The annulus helps to limit bending, twisting, shearing and distraction between the vertebral bodies.
The posterior longitudinal ligament, PLL, runs down the posterior aspect of the vertebral bodies, in the spinal canal. The PLL helps to limit the amount of flexion and distraction that occurs with the vertebrae. Just like the ALL, the PLL, has deep and superficial fibres. The deep fibres span 2 vertebrae, while the superficial fibres span upto 5 vertebrae. One unique feature of the PLL is its shape. It is a saw tooth like shape. It is narrow over the posterior aspect of the vertebrae but becomes wider over the posterolateral aspect of the disc. It helps to try and reinforce the weakest part of the annulus.
Just across the spinal canal, facing anteriorly, is the ligamentum flavum. The ligamentum flavum runs along the back, posterior, aspect of the spinal canal.
It is the front, anterior, aspect of the z joint capsule. The z joint capsule holds the synovial fluid in the joint to keep the joints lubricated. The ligamentum flavum has a unique property. It is made up of elastin, 80%. This means that the ligament is elastic. This ligament attaches the lamina of the vertebrae above to the lamina of the vertebrae below. The ligamentum flavum helps to limit z joint flexion. However, when the spine extends, bends backwards, because the ligament is elastic is gets smaller and does not fold into the spinal canal. This narrowing of the spinal canal would happen if the ligament was not elastic. That is so awesome the way the body was created! I really enjoy it when the anatomy of the body just makes sense.
Moving onto the intertransverse ligaments. These guys attach the transverse process’ of the vertebrae above and below. There are two layers of intertransverse ligaments, a dorsal and ventral, back and front. Between these layers are filled with fatty tissue, nerves and blood vessels. This ligaments could help to limit the amount of rotation and side flexion that occur.
Moving posteriorly, there is the interspinous ligaments. These run from the spinous process of the vertebrae below to the spinous process above. There are three different layers, anterior, middle and dorsal fibres. Even though these ligaments are very close to the near perfect orientation to limit flexion, they do not seem to offer much resistance to separation of the spinous process’.
Second to last ligament is the supraspinous ligament. This runs down the back aspect of the spine, going from spinous process to spinous process. This vertebra consists of superficial, middle and deep fibres. This ligament is unusual in the fact that it does not travel the entire length of the spine. The supraspinous ligament usually ends at L4-5. This leaves L5-S1 without a ligament to pull it posteriorly… or does it?
The last ligament that we are going to chat about only occurs at the L5-S1 level. Although, I do hear that sometimes, the iliolumbar ligament does extend to the L4 vertebrae as well. So we are going to chat about this iliolumbar ligament. This is a very large ligament with 5 different bands, anterior, superior, posterior, inferior and vertical. It basically locks the L5 vertebrae onto the pelvis, ilium. A couple of the bands attach where the quadratus lumborum muscle attaches on the ilium. I wonder if that give this ligament a little bit of an active component, if the quadratus lumborum is activated, it pulls on the ligament tightening it up to add more support?
We have talked about the bones, the discs and the ligaments of the lumbar spine. The main thing that is still missing are the muscles that control the lumbar spine. Let’s start with the small muscles in the lumbar spine and move outwards.
Multifidus is the deepest muscle in the ‘spinal gutter’. The ‘spinal gutter’ is the space in between the spinous process and the transverse process. Just lateral to the midline extending up to one inch off the midline. The multifidus is present throughout the entire spine. The muscle spans between the mammillary process, on the posterior aspect of the superior facet, and travels superomedially to attach on the spinous process of the vertebra above. Each multifidus attaches to 4 different spinous process, 2-5 vertebra above. This gives multifidus a very intimate connection to the lumbar spine. It helps to control the movement at each level in the spine.
Multifidus is an anticipatory muscle. That means that it actually comes on and stabilizes before you move. Yes, that is correct. When you are standing and think about walking across the room for a glass of water, before you even move your leg to take a step, the multifidi, plural, have helped to stabilize our spine before your first step!
However, not everything is grand in multifidus land. If you have a low back pain, within 24 hours the multifidus will start to waste away. In addition, it does not fire as an anticipatory muscle anymore. Why? Well we are not quite sure. Possibly the body thinks that if the multifidus fires, it will cause more pain or compression at the level the pain is coming from. This the is tricky part, after the low back pain is gone, there has been a lot of research that shows that multifidus does not automatically come back. It does not start firing/contracting at the level of the injury/pain. This could potentially lead to a weak spot in the back. This is where your physiotherapist comes in. There are specific core/abdominal/low back exercises that will get you to work on the multifidus and many other muscles. Not just working on contracting the muscles, which is great in itself, but get you thinking of working the muscles while moving. That is awesome stuff!
There are the interspinous muscles. Interspinous muscles are very deep and attach directly on the spine. These little muscles go between the spinous process of adjacent vertebrae. The muscles are too small to contract and cause movement of the spine. So it is thought that these little muscles might be ‘dynamic ligaments’. Muscles have more nerve endings that manage lengthening then ligaments do. These muscles might work subconsciously to provide information to the nervous system about where the vertebra are in space and possibly give a painful spasm if you are bending too far forward, for example.
Heading just laterally, we go to the intertransverse muscles. Just like the intertransverse ligaments, these muscles go from one transverse process of the vertebrae above to the transverse process of the vertebrae below. Similarly to the interspinous muscles, these are thought to be ‘dynamic ligaments’. They are too small to actually cause movement of the spine when they contract but they might because to limit motion or brace and allow motion to occur at a slow pace. Potentially limiting damage to the low back. Ironically, these muscles tightening up to limit motion/injury might give a spasm which will hurt and give low back pain.
One possibility of the low back muscles is that if pain occurs, this may limit all their activation and in turn make it easier to hurt your back again. Making a ‘weak spot’ in the back. Most people say that they have a area in their back, if they get recurring back pain, the pain seems to always come back to the same spot. If an injury occurs to the interspinous or -transverse muscles and there is an inflammatory response, maybe that is what shuts down the multifidus muscle. We then to think of one structure getting inflamed and that is it. However, in reality, inflammation is a three dimensional process. The inflammation spreads out in all directions and it causes irritation in tissues that were not injured.
Those are the teeny-tiny little muscles of the low back. Getting to the larger muscles, we have the erector spinae muscles. This is a group of three muscles. The erector spinae group of muscles occur on both sides of the spine. The three muscles, going lateral to medial, are; iliocostalis, longissimus and spinalis. Let’s break this down and talk about them individually.
Iliocostalis is the muscle furthest from the spine, the most lateral. There is a portion that comes from the thoracic spine and goes to the lumbar spine and a portion only in the lumbar spine. It comes from the erector spinae aponeurosis in the lumbar spine area. This fascia is also where longissimus originates from. So these two muscles are very difficult to differentiate from their attachment point in the low back, erector spinae aponeurosis. However, iliocostalis goes up and lateral and it attaches on the rib angle in the thoracic spine, approximately the lower 7-8 ribs. This muscle is innervated by the lateral branch of the dorsal ramus. The dorsal ramus branches into three nerves, the medial, intermediate and lateral branches. More on them later.
The lumbar portion of iliocostalis comes from the posterior aspect of the transverse process, L1-4, and attaches on the superior portion of the iliac crest. According to Bogduk, in the 3rd edition of Clinical Anatomy of the Lumbar Spine and Sacrum, there is an L5 fascicle however, it is not muscular, it is part of the iliolumbar ligament, as mentioned above.
Longissimus is the middle muscle of the erector spinae trio. Like iliocostalis, there are two parts to this muscles we are going to concern ourselves with. Iliocostalis is supplied by the intermediate branch of the dorsal ramus. There are thoracic and lumbar portions. The thoracic portion attaches on the transverse process’ of the thoracic spine, as high as T1 or T2. It goes inferiorly and attaches on the spinous process of the lumbar and sacrum, as part of the erector spinae aponeurosis.
What is an aponeurosis? Well according to Google/Wikipedia it is a broad tendon made up of multiple flat layers. If you search on Google and choose the Wikipedia page, there is a picture of the lumbar aponeurosis. But I digress…
The lumbar portion attaches on the posterior aspect of the transverse process, but more medially than that of iliocostalis. This attaches, just medial to the attachment of iliocostalis on the iliac crest.
The most medial muscle of the erector spinae trio is spinalis. Spinalis is the superficial muscle in the ‘spinal gutter’. Spinalis attaches from the spinous process’ in the upper L-spine, L1 and 2, as well as the lower thoracic spine, T11 and 12. The muscle travels superiorly, staying close to the spine, and attach to the mid thoracic spinous process’.
Covering the erector spinae musculature is the thoracolumbar fascia, TFL. The thoracolumbar fascia is made up of 3 layers, anterior, middle and posterior layers. This is a thick, strong ligament type structure. Latissimus dorsi (‘lats’) and gluteus maximus (your butt muscle) attach directly onto the thoracolumbar fascia. They attach at opposite corners, for example lats attach in the upper left and right attachments and the glute max attaches in the lower quadrant attachments. The thoracolumbar fascia attaches the two muscles, the fibres from the left lat travel downward and medially to the lumbar spine, while the fibres from the right glute max travels superiorly and medially. The meet at the midline and are separate. However, the lower the fibres are, below L4, they can cross the midline and directly attach left lat/right glute max and right lat/ left glute max. The posterior layer of the TFL attaches to the above muscles but also to the spinous process. This helps to resist forward movement of the vertebrae with forward bending/ flexion. The posterior layer and middle layer surround the erector spinae muscles. The middle layer separates the anterior aspect of the erector spinae muscles and the posterior aspect of quadratus lumborum. The anterior layer of the TFL covers the anterior aspect of quadratus lumborum. All three layers of the TFL come together and create the tendon attachment of transversus abdominis. There is a reason that the TFL engulfs and is attached to all those muscles. When the thoracolumbar fascia gets tension on it, it causes the erector spinae muscles to contract more strongly. This is called the ‘hydraulic amplification effect’. Basically the muscles contract in a tight tube, the TFL, this compress stimulates the muscles to contract more. This extra compression can increase strength upto 30%, via mathematical calculations beyond my ability.
Quadratus lumborum, QL, is an interesting muscle. It attaches to the inferior aspect of the 12th rib as well as the anterior portion of the transverse process, L1-4. Those bands of muscle converge onto the iliac crest, partially surrounded by parts of the iliolumbar ligament. Initially, this muscle, QL, was thought to only aid in deep breathing, to fix the 12th rib inferiorly. However, now there is evidence that this muscle also helps to stabilize the pelvis when doing strenuous unilateral activity. For example, carrying a bunch of bags of groceries in one hand as you hold your keys in the other hand to open the door. This muscle is also surrounded by the middle and anterior layers of the thoracolumbar fascia, possibly giving a ‘hydraulic amplification effect’, as well.
Transversus abdominis is the final muscle we will discuss. Way back, when I was a little guy, I remember hearing that doing sit-ups could strengthen your low back. It was because of this muscle, transversus abdominis. We know that transversus abdominis, TA, is a very important muscle for low back stability. TA was highlighted in 1999, I believe, by Paul Hodges and his research group in Australia. They showed that TA is an anticipatory muscle, just like multifidus. It did not matter which direction your arms or legs are going to move in, TA contacted before the movement occurred to ‘brace’ the spine. They also published that if the person has low back pain, TA stops working like that. It does not come on, as soon, before movement or it comes on after movement occurs. In addition, just like multifidus, when the back pain is gone, TA does not return to the anticipatory stage automatically. Possibly setting the person up for another back injury. They were incredible findings and I know many physiotherapists swear by doing lots of TA activation exercises.
TA is an extension of the thoracolumbar fascia. After the anterior, middle and posterior bands join one tendon, that tendon turns into the TA muscle. TA also comes off the iliac crest, and the lateral ⅓ of the inguinal ligament, up front. Both sides meet at the linea alba. The linea alba is the centre line of the abdominal muscles. It divides the left and right sides of the six pack abs. This makes TA the deepest abdominal muscle we have, so it cannot be seen! Your physiotherapist will help to teach you how to activate your TA, during your recovery of low back pain. While it is only one muscle, it can make a difference. The thought is that you contracting your TA, and multifidus contracts with it at the same time as well, is that your body starts to get it contracting in an anticipatory fashion. Unfortunately, there is no evidence, that I know of, that supports this theory. There is some good scientific evidence that does support the use of these exercises. I have not read this study in a number of years, so I might get some of the basics incorrect, maybe someone could send me the reference to the following study. The study was done in Australia and it looked at whether or not TA exercises helped people to recover faster from low back pain. It was physiotherapy vs physiotherapy and TA exercises. There was no difference in the speed of recovery. However, they looked back after 2 years and discovered that people that did the exercises had an 80% less chance of have a recurrence of low back pain. Even though the exercise seems to be so little and minuscule, do the exercise, if I give it to you it is for a good reason. I swear it is not for you to waste your time.
Next… up are the nerve of the lumbar spine. There are a few noteworthy nerves. We are going have a gander at the ventral and dorsal rami and see where the different branches go. The nerve root comes off the spinal cord and splits into two different nerve, the ventral (front) and the dorsal (back) rami. I remember this by thinking about sharks. Sharks have a dorsal fin that comes out of the water and scares people. The dorsal fin is on the sharks back. So dorsal in anatomical terms means back, just one of the weird ways I remember certain things. I almost forgot about the sympathetic nerve trunks. They are on the anterolateral aspect of the vertebral bodies. These are important as you will see there are some branches better the sympathetic and regular nerves.
The ventral ramus divides into two different branches, skeletal and muscular. So what does this nerve supply? The ventral rami pierce the intertransverse ligaments and lie between the two layers. The ventral rami of the lumbar spine help to form the lumbar plexus, L1-4 and the L4 and L5 ventral rami join to form the lumbosacral trunk. The lumbosacral trunk joins the lumbosacral plexus.
The muscular branches innervate QL, psoas and the small intertransversarii muscles.
The skeletal branch connects with the grey rami communicans, from the sympathetic nerves, and supplies the anterior longitudinal ligament, anterior and lateral aspects of the annulus.
Another branch of the ventral ramus attaches with the gray ramus communicans to form the sinuvertebral nerve. This nerve is formed after the ventral ramus has left the spinal canal and it turns around and heads back into the intervertebral foramen. The sinuvertebral nerve innervates the posterior longitudinal ligament, the posterior and posterolateral annulus as well as the ventral dural sac and the basivertebral and epidural veins.
The dorsal ramus divides into three branches, medial, intermediate and lateral.
The lateral branch of the dorsal ramus goes to iliocostalis, lumbar and thoracic portions, the thoracolumbar fascia and the L1-3 cutaneous branches. These cutaneous branches can travel as far as the greater trochanter of the femur.
The intermediate branch is simple. It supplies the longissimus muscle. Interesting note, sometimes the intermediate branch is missing. Well instead of being its own branch what it does it becomes a branch off the lateral branch. It still supplies longissimus, no matter where it originates from.
The medial branch of the dorsal ramus is a good one to remember. It supplies goes to the z joints, the level it is at and the level below. So each z joint has two medial branches supplying it. In addition, basically any muscle that comes off the spinous process, is innervated by this nerve. The interspinous muscles and multifidus are both innervated by the medial branch of the dorsal ramus. Interestingly enough, this nerve also only innervates those muscles at the level in which it comes out at. For example, the L3 branch will only innervate the L3 multifidus and interspinous muscles. This, in fact, creates one of the pure myotomes of the body, muscles purely innervated by one segmental level of the spine. Too bad the muscles are too small to actually test for fatigable weakness or decreased reflexes.
I think the most important things to take away from the above is that the disc is innervated by the sinuvertebral nerve and the z joints are innervated by the medial branch of the dorsal ramus.
Last, but not least, is the vasculature to and from the lumbar spine. The arteries and veins which supply this region are not commonly discussed.
The arteries for the lumbar spine come straight off the aorta. The vessels travel along each nerve and enter the intervertebral foramen. The artery has two choices; it can stay with the nerve all the way to the end of its course or it can diverge from the nerve root. The diverging artery will the attach to either, or both, the anterior spinal artery or the posterior spinal arteries. If the artery takes the first option, stays with the nerve all the way to the end of its course, it is called a radicular artery. If option number two is more appealing, the artery supplies the nerve but the takes off and heads for the anterior/ posterior spinal arteries, it is called a medullary artery. The spinal arteries, anterior and posterior, get most of their blood through medullary arteries. The initial branch off the basilar artery that starts the anterior and posterior arteries is not sufficient to supply the entire spinal cord. Therefore, medullary arteries come in to supplement the blood supply to the spinal cord. There is one large medullary artery that arrives just above the lumbar spine. It is called the Great Medullary Artery or the Artery of Adamkiewicz. It typically enters through the 9th – 12th intercostal arteries and attaches to the anterior spinal artery, helping to supply the lower ⅓ of the spinal cord.
There are branches off the radicular and medullary arteries at each level, anterior and posterior spinal canal branches. Those supply the vertebral bodies, the ligaments and muscles at each level.
The lumbar veins have a simple path back to the heart. Like most parts of the body, the veins and arteries run together. The basivertebral veins leave the vertebral bodies. These veins drain mostly to the posterior of the vertebral body into the anterior internal vertebral venous plexus. At every level, the anterior internal vertebral venous plexus sends off branches to the ascending lumbar vein. The ascending lumbar vein then communicates with the common iliac vein, inferiorly. Superiorly, the ascending lumbar vein attaches to the azygous vein, on the right and hemiazygous vein on the left. Around T12, these veins come together with some other and join the superior vena cava.
That is all, and more, that I know about the lumbar spine. It is amazing how much I actually knew to write this huge post, my biggest one ever! But I did get some help from Wikipedia, Magee’s Orthopaedic Physical Assessment, 5th edition, Bogduk’s 3rd edition of Clinical Anatomy of the Lumbar Spine and Sacrum as well as from the Orthopaedic Division’s Theory II manual and Level II Lower clinical manual and lastly my own brain.