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The Lumbar Spine Masterclass, Part 4

We are half way through our Lumbar Spine Masterclass. Have you learned anything yet?

We have talked about the bones (Part 1), the discs (Part 2) and the ligaments (Part 3) 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 nerves of the lumbar spine.

If you have any questions or comments about the Lumbar spine, please click here to contact New Leaf Physio, a mobile Kelowna physiotherapy clinic.

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