“Oh, my Sciatica!”- Definition, Causes and Conditions

Orthopaedic & Spine Center


Image of Dr. Jeffrey CarlsonJeffrey R. Carlson, MD

We’ve all heard someone in our life speak of sciatic pain. What exactly is it, and what can we do about it?

Sciatic pain (called sciatica) begins in the sciatic nerve, which is the largest single nerve in the body. It is comprised of individual nerve roots in the lower back that combine to form the sciatic nerve. It runs from the lower back, through the buttock, and down the back of each leg. Portions of the sciatic nerve then branch out to parts of each leg—the thigh, calf, foot, and toes.

Sciatica is not a medical diagnosis, but rather, it is a symptom of an underlying medical condition. Sciatica symptoms occur when the large sciatic nerve is irritated or compressed at or near its point of origin. Sciatica is often characterized by one or more of the following symptoms:

  • Constant pain in only one side of the buttock or leg (rarely in both legs)
  • Pain that is worse when sitting
  • Leg pain that is often described as burning, tingling, or searing (versus a dull ache)
  • Weakness, numbness, or difficulty moving the leg, foot, and/or toes
  • A sharp pain that may make it difficult to stand up or walk
  • Pain that radiates down the leg and possibly into the foot and toes (it rarely occurs only in the foot)

The symptoms are usually based on where the nerve is pinched or compromised. For example, a lumbar segment 5 (L5) nerve impingement can cause weakness in extension of the big toe and possibly in the ankle. When you tell your physician exactly what you are feeling and where, he or she is able to more accurately pinpoint where to target imaging and treatment.  Back pain is not sciatica.

What causes sciatica? There are several common causes:

  • 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 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 – disc degeneration is a natural process that occurs with aging, but for some people one or more degenerated discs in the lower back can also irritate a nerve root and cause sciatica. Degenerative disc disease presents when a weakened disc has excessive micro-motion, causing inflammatory proteins from inside the disc to become exposed and irritate the nerve root(s) in the area. Bone spurs, which may develop with spinal degeneration, also may press against a nerve, resulting in sciatica.
  • SpondylolisthesisSpondylolisthesis occurs when one vertebral body to slip forward on another. The combination of disc space collapse and the vertebral body slipping forward can cause a nerve to get pinched, subsequently causing sciatica.
  • Lumbar spinal stenosis – Stenosis is the narrowing of the spinal canal, and this condition commonly causes sciatica due to the narrowing. Lumbar spinal stenosis is related to natural aging in the spine and is relatively common in adults older than age 60. Stenosis typically results from a combination of one or more of the following: enlarged facet joints, bone spurring from arthritis or an overgrowth of the soft-tissue around the facet joints.
  • Piriformis syndrome –The piriformis is a muscle in the buttocks. The sciatic nerve can get irritated as it runs under this muscle. If the piriformis muscle irritates or pinches a nerve root that comprises the sciatic nerve, it can cause sciatica-type pain. 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.
  • Sacroiliac joint dysfunction – The sacroiliac (SI) joint is located at the bottom of the spine. If that joint gets irritated or inflamed, it can bother the L5 nerve, which lies on top of the sacroiliac joint. This can cause sciatica-type pain. Again, this is not a true radiculopathy, but the leg pain can feel the same as sciatica caused by a nerve irritation.

In addition to the most common causes, other conditions can cause sciatica and sciatica symptoms, including:

  • Scar tissue – If scar tissue—also called epidural fibrosis—compresses to a lumbar nerve root, it can cause sciatica. The formation of scar tissue is part of the normal healing process that the body goes through after some spine surgeries. Unfortunately, the build-up of too much scar tissue can cause nerve impingements causing postoperative back or leg pain. Scar tissue is a common cause of Failed Back Surgery Syndrome.
  • 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 it is more common for spinal tumors to develop as cancer from a different part of the body spreads to the spine.
  • 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 pain during pregnancy. Lower back pain is very common during pregnancy, but this is not related to sciatica.
  • Muscle strain – Inflammation stemming from a lower back muscle strain and/or muscle spasm can put pressure on a nerve root and cause sciatica pain.

In Part Two of this article, I will discuss the non-surgical treatments for Sciatica.