The base of the spine is made up of the intricate L5-S1 vertebral segment, also called the lumbosacral joint. This spinal segment has several interconnected components, any of which can cause lower back and/or leg pain (sciatica):
- The lowest of the lumbar spine's five vertebrae (called L5) can slip forward over the first vertebra of the sacrum (called S1) and cause pain by compressing the nerve root
- The L5-S1 disc, which lies between the L5 and S1 vertebrae, can lead to leg pain and/or lower back pain if the inner portion of the disc herniates or if the disc degenerates
- The L5 and S1 vertebrae are connected in the back of the spine by two joints called facet joints (or zygapophyseal joints), which can lead to pain if they allow abnormal amount of motion or degenerate
- There is a nerve that passes from the spinal canal through an opening in the back of the L5-S1 segment and runs down the back of each leg (as part of the large sciatic nerve). This nerve is called the L5 nerve root. It can lead to leg pain (sciatica) if any structure presses against it or if the highly inflammatory proteins from the inner portion of the disc leak out and touch it.
The structures in this lumbosacral segment combine together to provide both a strong and stable base for the spine and a multifunctional joint that allows the torso to twist and bend in all directions.
Because of the force on this segment, as well as the range of motion it provides, it is susceptible to injury - both in terms of acute injury and/or degeneration due to wear and tear over time.
Causes of L5-S1 Pain
The most common causes of pain that originate in the lumbosacral segment L5-S1 include:
- L5-S1 disc herniation: The disc becomes herniated when the inner portion leaks out and touches the nearby nerve root, causing pain to radiate in the lower back and/or down the leg.
- L5-S1 degenerative disc disease: If the L5-S1 disc is compromised, the L5-S1 disc itself can become a source of lower back and/or leg pain.
- L5-S1 Isthmic Spondylolisthesis: A small fracture in the facet joints can allow the L5 vertebra to slip forward over the S1 vertebra, impinging the nerve root and leading to leg pain and other symptoms.
There are also a number of spinal conditions that can run through multiple levels the lumbar spine and affect the L5-S1 lumbar segment, such as osteoarthritis of the lower back and lumbar spinal stenosis.
Because there is no spinal cord in the lumbar spine, even very painful conditions are unlikely to cause paralysis or permanent damage. See When Back Pain May Be a Medical Emergency
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Lumbosacral Joint Treatment
It is advisable for patients to seek a diagnosis from a physician or chiropractor to identify the underlying cause of their L5-S1 pain and determine the most appropriate treatment. In most cases, L5-S1 treatment begins with non-operative solutions.