Anatomy of the lower back and pelvis explained

To help you best understand how the lower back can be injured or hurt, it’s important to understand what comprises the area and therefore the potential for injury when you feel pain. Our lower back, by its anatomical description, is the lumbar spine. The lumbar region is the area of the body located below the bottom rib, and extending to the top of the pelvic bones at the top of the hip. So, let’s discuss what is in the lumbar region – some of these might sound very familiar to you.

There are 5 vertebrae, or bones, that comprise the lumbar spine and the structure of these reflects the role these are designed to play. They are larger and more square-shaped than the other vertebrae found in the spine, largely because they need to support the weight of the upper body. They also allow us to bend forward and backwards, with a little bit of rotation as well. These movements are allowed by the joints that sit either side of the bones called the facet joints. We have another joint between each of the vertebrae and these are separated by the intervertebral discs.

The role of the disc is to allow for cushioning or shock absorption through the spine, plus avoid bones from contacting directly on one another. Within the disc itself, there are two components – the nucleus pulposis and the annulus fibrosis. These are basically the inner and outer parts of the disc. Sometimes, injury can occur when the nucleus pulposis presses more firmly on one are of the outer layer (annulus fibrosis). Historically, these have been referred to as disc bulges. Outside of the bones and discs, we also have ligaments that are thick, strong tissue types that help to strengthen and stabilise the back. We have ligaments that surround almost every joint in our bodies, and sometimes we over-stretch these ligaments and they can tear or sprain, and cause significant levels of pain.

Other than the spine and bony architecture of the back, we also have lots of nerves and muscles that allow us to both stabilise the spine and move the spine. We have core muscles like multifidis that give really good stability around the back, and then the erector spinae and quadratus lumborum muscles. The names are long and complicated, but it describes their position and their function at times too. Like any muscle in the body, at times we can have an injury when we strain a muscle and place it under a load that is too high for the strength of that muscle. Sometimes, because of the sensitive nature of the spine, we can experience very high and debilitating levels of pain in the lumbar spine, even if the level of damage to the muscle or joint is low.

Not to be missed in the lumbar spine is the joint between the spine and the pelvis – the sacroliliac joint. The name describes exactly where it is – between the sacrum, our tail bone, and the iliac part of the pelvis. This is one of the strongest and thickest joints in our bodies and has very little movement typically. Where we see injury or pain to the SIJ is in pregnant women whose joints are moving more than usual due to the hormonal changes in pregnancy. The good news is, that like all other back injuries, with a combination of supports and strength work, SIJ injuries can be well managed by Pilates and physiotherapy treatment alone. For more information, check out our Instinct Health webpage and book an appointment today!

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Anatomy of the lower back and pelvis explained