Lumbosacral Angle

The Lumbosacral Angle, Your Spinal Curves and Your Back Pain

Model of the lumbosacral spine from the back.
Model of the lumbosacral spine from the back. MedicalRF.com/MedicalRF.com/Getty Images

One thing's for certain — the field of back pain and spine is teeming with technical terms. In this article, you'll learn about the lumbosacral angle — what it is and why it's important.

Quick Spinal Anatomy Review

The spine has four main curves. They are categorized in terms of regions, which are:

  • Cervical, or neck
  • Thoracic, or upper and mid-back area
  • Lumbar, which is your low back, and,
  • Your sacral curve, located at the base of your spine.

The directions of these curves alternate — one right after another. This construction feature helps provide both support and balance to your body as you go through your day. Common positions and movements such as sitting, standing, walking, bending reaching, twisting and lifting benefit greatly from the alternating directions of spinal curves.

The entirety of the spine from the neck down through the lowest lumbar vertebra, which is called L-5, rests onto the top of the sacrum. This bottom joint, called L5 - S1, is also known as the lumbosacral joint. 

The sacrum is a triangular bone that is wedged in between the two hip bones in back to help stabilize the column, and to ease the load of your spine as it transfers down to your lower body. It achieves these feats by distributing the weight of your spine throughout the pelvis and down into lower extremity.

Along with a lumbosacral joint, there's a lumbosacral spine, according to Renee Calliet, MD and author.

Calliet says the lumbosacral spine is comprised of the five lumbar segments, including that lowest L5 - S1 joint. A "segment" is basically an intervertebral joint which consists of an upper spinal bone and a lower spinal bone with a disc in between.

By the way, each region of the spine has a specific number of these segments. The neck has seven, thoracic spine, twelve, lumbar spine, five and sacral spine one. The sacral spine is made up solely of the sacrum bone, but that bone is itself made of five individual bones that fuse, in most people, by the age twenty-six.

The Lumbosacral Angle Defined

And now, for the lumbosacral angle. Because your whole spine sits on top of that lowest sacrum bone, the angle of the top of the sacrum determines the degree of each of the spinal curves located above it. This includes the lumbar, thoracic and cervical curves.

As you can likely imagine, the weight of your upper body transfers from the spine through the L5 vertebra to the sacrum. The top of the sacrum bone is called the sacral base and it is not horizontal. Rather, it tilts. The degree of sacral base tilts vary in individuals; they can be, relatively speaking, steep or flat, or places in between. 

As the base of support for the spine, then, this sacral angle determines, at least in part, the degree of curve in the lumbar, thoracic and cervical areas. In other words, starting at the foundation, which, again is the top of the sacrum, and going up the spine, one angle influences another. 

The Lumbosacral Angle and Spondylolisthesis

One common spinal problem that occurs at the L5-sacrum joint is called spondylolisthesis. Spondylolisthesis is a forward slippage of the top bone, the L5, relative to the bottom bone, the sacrum. 

This condition affects young and old alike, though in different forms. 

In children and adolescents, it tends to start as injury, like a hairline fracture, to a small area at the back of the spine known as the pars interarticularis. Young athletes are most at risk, especially when their sports require repetitive forward and back spinal movements. Examples include cheerleaders and football players.

Over time, the pars injury can develop into spondylolysis and finally spondylolisthesis.

In older people, spondylolysis and spondylolisthesis tend to be caused by degenerative changes in the spine. 

A study published in March 2008 issue of The Journal of the Bone and Joint Surgery, reported that among other things, a greater “incline” of the sacral table, as they call the sacral base, is associated with a higher incidence of spondylolisthesis.  

Can you Exercise Your Lumbosacral Angle into a Better Position?

You may be wondering if it's possible to correct an excessive lumbosacral angle, that you think may be at the root of your chronic back pain, with exercise.

A 2018 study published in the Journal of Physical Therapy Science looked at the results of a twelve week lumbar stabilization program to determine the answer to this and other related questions.

The researchers found that while such a program helped strengthen core muscles, i.e., those muscles most responsible for stabilizing the spinal column, especially in the upright position, it did not actually alter the lumbosacral angle. Instead, the study authors surmise, the reduction in pain after the twelve weeks of work was likely due to increased muscle strength and joint flexibility lessening load placed on the spine.

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