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Causes

By Mayo Clinic staff

Your sciatic nerve branches from your spinal cord through your hips and buttocks and down the back of each leg. This nerve controls many of the muscles in your lower legs and provides feeling to your thighs, legs and feet. Sciatica may develop when a nerve root is compressed in your lower (lumbar) spine — often as a result of a herniated disk in your lower back.

Disks are pads of cartilage that separate the bones (vertebrae) in your spine. Filled with a gel-like substance, they keep your spine flexible and act as shock absorbers to cushion the vertebrae when you move.

If the outer covering of a disk tears (herniates), gel may seep out and press on a nerve root, causing pain in your back, leg or both. If the damaged disk is in the lower part of your back, you may also experience numbness, tingling or weakness in your buttock, leg or foot.

Although a herniated disk is a common cause of sciatic nerve pain, other conditions also can put pressure on your sciatic nerve, including:

  • Lumbar spinal stenosis. Spinal stenosis is a narrowing of one or more areas in your spine — most often in your upper or lower back. When the narrowing occurs in the lower spine, the lumbar and sacral nerve roots may be affected.
  • Spondylolisthesis. This condition, often the result of degenerative disk disease, occurs when one vertebra slips slightly forward over another vertebra. The displaced bone may pinch the sciatic nerve where it leaves your spine.
  • Piriformis syndrome. The piriformis muscle starts at your lower spine and connects to each thighbone (femur). Piriformis syndrome occurs when the muscle becomes tight or goes into spasms, putting pressure on the sciatic nerve. Prolonged sitting, car accidents and falls can contribute to piriformis syndrome.
  • Spinal tumors. In the spine, tumors can occur inside the spinal cord, within the membranes (meninges) that cover the spinal cord, or in the space between the spinal cord and the vertebrae. As it grows, a tumor compresses the cord itself or the nerve roots.
  • Trauma. A car accident, fall or blow to your spine can injure the lumbar or sacral nerve roots.
  • Sciatic nerve tumor or injury. Sometimes, the sciatic nerve itself may be affected by a tumor or injury.
  • Other causes. In some cases, your doctor may not be able to find a cause for your sciatica. A number of problems can affect your bones, joints and muscles, all of which could potentially result in sciatic pain.
References
  1. Lin M. Musculoskeletal back pain. In: Marx JA, et al., eds. Rosen's Emergency Medicine: Concepts and Clinical Practice. 6th ed. St. Louis, Mo.: Mosby; 2006. http://www.mdconsult.com/book/player/book.do?method=display&type=bookPage&decorator=header&eid=4-u1.0-B978-0-323-05472-0..00051-7--s0045&displayedEid=4-u1.0-B978-0-323-05472-0..00051-7--s0060&uniq=184337872&isbn=978-0-323-05472-0&sid=955285604. Accessed March 1, 2010.
  2. Rosenbaum RB, et al. Degenerative disease of the spine. In: Bradley WG. Neurology in Clinical Practice. 5th ed. Burlington, MA: Butterworth-Heinemann; 2008. http://www.mdconsult.com/book/player/book.do?method=display&type=bookPage&decorator=header&eid=4-u1.0-B978-0-7506-7525-3..50115-1--cesec38&displayedEid=4-u1.0-B978-0-7506-7525-3..50115-1--cesec55&uniq=184337872&isbn=978-0-7506-7525-3&sid=955285604. Accessed March 1, 2010.
  3. Gregory DS, et al. Acute lumbar disk pain: Navigating evaluation and treatment choices. American Family Physician. 2008;78:835.
  4. Aminoff MJ. Mechanical and other lesions of the spine, nerve roots, and spinal cord. In: Goldman L, et al., eds. Goldman: Cecil Medicine. 23rd ed. Philadelphia, Pa.: Saunders Elsevier; 2007. http://www.mdconsult.com/das/book/body/184337872-18/0/1492/1420.html#4-u1.0-B978-1-4160-2805-5..50428-6--cesec37_17875. Accessed March 1, 2010.
  5. Devereaux M. Low back pain. Medical Clinics of North America. 2009;93:477.
  6. Low back pain fact sheet. National Institute of Neurological Disorders and Stroke. http://www.ninds.nih.gov/disorders/backpain/detail_backpain.htm#119483102. Accessed March 1, 2010.
  7. Wheeler SG, et al. Approach to the diagnosis and evaluation of low back pain in adults. http://www.uptodate.com/home/index.html. Accessed March 1, 2010.
  8. Knight CL, et al. Treatment of acute low back pain. http://www.uptodate.com/home/index.html. Accessed March 1, 2010.
  9. Ernst E. Complementary treatments in rheumatic diseases. Rheumatic Disease Clinics of North America. 2008;34:455.
  10. Chronic pain: Hope through research. National Institute of Neurological Disorders and Stroke. http://www.ninds.nih.gov/disorders/chronic_pain/detail_chronic_pain.htm. Accessed March 1, 2010.
  11. Laskowski ER (expert opinion). Mayo Clinic, Rochester, Minn. March 4, 2010.
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