When discussing sciatica, it is important to understand the underlying medical cause, as effective treatment will focus on addressing the pain’s root cause as well as alleviating acute symptoms.
6 Most Common Causes of Sciatica
The following six lower back problems are the most common causes of sciatica:
Lumbar herniated disc
A herniated disc occurs when the soft inner material of the disc leaks out, or herniates, through the fibrous outer core and irritates or pinches the contiguous nerve root.
Other terms used to refer to a herniated disc are slipped disc, ruptured disc, bulging disc, protruding disc, or a pinched nerve. Sciatica is the most common symptom of a lumbar herniated disc.
Degenerative disc disease
While some level of disc degeneration is a natural process that occurs with aging, for some people one or more degenerated discs in the lower back can also irritate a nerve root and cause sciatica.
This condition occurs when a small stress fracture allows one vertebral body to slip forward on another; for example, if the L5 vertebra slips forward over the S1 vertebra.
Lumbar spinal stenosis
This condition commonly causes sciatica due to a narrowing of the spinal canal. Lumbar spinal stenosis is related to natural aging in the spine and is relatively common in adults older than age 60.
The sciatic nerve can get irritated as it runs under the piriformis muscle in the buttock. If the piriformis muscle irritates or pinches a nerve root that comprises the sciatic nerve, it can cause sciatica-type pain.
Sacroiliac joint dysfunction
Irritation of the sacroiliac joint—located at the bottom of the spine—can also irritate the L5 nerve, which lies on top of the sacroiliac joint, causing sciatica-type pain.
Degenerative disc disease is diagnosed when a weakened disc results in excessive micro-motion at that spinal level, and inflammatory proteins from inside the disc become exposed and irritate the nerve root(s) in the area.
Read more: Lumbar Degenerative Disc Disease (DDD)
Bone spurs, which may develop with spinal degeneration, also may press against a nerve, resulting in sciatica.
Read more: Bone Spurs (Osteophytes) and Back Pain
With a combination of disc space collapse, the fracture, and the vertebral body slipping forward, the nerve can get pinched and cause sciatica.
Read more: Isthmic Spondylolisthesis
The condition typically results from a combination of one or more of the following: enlarged facet joints, overgrowth of soft tissue, and a bulging disc placing pressure on the nerve roots, causing sciatica pain.
Lumbar spinal stenosis commonly occurs along with spinal arthritis, and arthritis can also cause or contribute to sciatica symptoms.
Read more: Lumbar Spinal Stenosis: A Definitive Guide
This is not a true lumbar radiculopathy, which is the clinical definition of sciatica. However, because the leg pain can feel the same as sciatica or radiculopathy, it is sometimes referred to as sciatica.
Read more: What is Piriformis Syndrome?
Again, this is not a true radiculopathy, but the leg pain can feel the same as sciatica caused by a nerve irritation.
Read more: Sacroiliac Joint Dysfunction (SI Joint Pain)
In This Article:
More Causes of Sciatica and Sciatica-Type Symptoms
In addition to the most common causes, a number of other conditions can cause sciatica, including:
- Pregnancy. The changes the body goes through during pregnancy, including weight gain, a shift of one's center of gravity, and hormonal changes, can cause sciatica during pregnancy.
- Scar tissue. If scar tissue—also called epidural fibrosis—compresses to a lumbar nerve root, it can cause sciatica.
- Muscle strain. In some cases, inflammation related to a lower muscle strain and/or muscle spasm can put pressure on a nerve root and cause sciatica pain.
- Spinal tumor. In rare cases, a spinal tumor can impinge on a nerve root in the lower back and cause sciatica symptoms. It is possible for tumors to originate in the spine, but more commonly spinal tumors develop as cancer from a different part of the body metastasizes and spreads to the spine.
- Infection. While rare, an infection that occurs in the low back can affect the nerve root and cause sciatica.
- Fracture. If a fracture occurs in a lumbar vertebra, it is possible for symptoms to include sciatica. Most fractures occur because of a serious trauma (such as a car accident or a fall) or because the bone has become weak due to osteoporosis or another underlying condition or medication.
- Ankylosing spondylitis. This condition is characterized by chronic inflammation in and around the spine. Often symptoms first show up in the sacroiliac joints, causing sacroiliitis, and symptoms may include sciatica.
The above is not a complete list. It is important to know the underlying clinical diagnosis of the cause of sciatica, as treatments will often differ depending on the cause. For example, specific sciatica exercises, which are almost always a part of a treatment program, will be different depending on the underlying cause of the symptoms.
Risk Factors for Developing Sciatica
Some research indicates that those who are overweight, obese, or who smoke are at added risk of developing sciatica and of requiring hospitalization for sciatica.3,4 Tobacco use, or any type of nicotine intake, has been shown to contribute to disc degeneration.5,6
- Shiri R, Lallukka T, Karppinen J, Viikari-Juntura E. Obesity as a Risk Factor for Sciatica: A Meta-Analysis. Am. J. Epidemiol. 2014. doi:10.1093/aje/kwu007. aje.oxfordjournals.org/content/179/8/929.long.
- Shiri, Rahman et al. The Effect of Smoking on the Risk of Sciatica: A Meta-analysis. Am J Med. 2016 Jan;129 (1):64-73.e20. doi: 10.1016/j.amjmed.2015.07.041. American Journal of Medicine, Volume 129, Issue 1, 64-73.e20. www.ncbi.nlm.nih.gov/pubmed/26403480.
- Haugen AJ, Brox JI, Grovle L, et al. Prognostic factors for non-success in patients with sciatica and disc herniation. BMC Musculoskelet Disord. 2012;13:183. bmcmusculoskeletdisord.biomedcentral.com/articles/10.1186/1471-2474-13-183.
- Miwa S, Yokogawa A, Kobayashi T, et al. Risk factors of recurrent lumbar disc herniation: a single-center study and review of the literature. J Spinal Disord Tech. 2015;28:E265-E269. www.ncbi.nlm.nih.gov/pubmed/23249886.