Causes of Sciatica and Sciatic Nerve Pain

The Universal Guide to Sciatica Causes: Everything you ever wanted to know, straight from the experts.

In This Article:Top Causes   |    Herniated Discs   |    Degeneration   |    Stenosis   |    Spondylolisthesis   |    Trauma   |    Piriformis Syndrome   |    Tumors   |    Risk Factors  |    FAQs

You might be surprised to learn that sciatica isn’t a condition, but a description of symptoms caused by other conditions in your lower back. You also might not care, because whatever it is, sciatica hurts.

Sciatica is the name of the pain from when something—usually a herniated disc, but other causes are possible too—compresses, irritates or inflames the sciatic nerve or one of the nerve roots that eventually become the sciatic nerve. Translation: pain up and down your leg—you might feel it anywhere from your buttocks to your ankle.

Want to know how to get rid of your sciatica? The first step is understanding the root cause. Read on to learn about some of the most common sciatica causes—and what to do about them.

 

The sciatic nerve runs from the back, under the buttock, and downward through the hip area into each leg. Photo Source: 123RF.com.

“Sciatica is actually a symptom of an underlying problem,” says Brian R. Subach, MD, a neurosurgeon who practices at National Spine and Pain in Maryland.. There are several spinal disorders can cause sciatic nerve compression. The six most common are:

Though all of these can be responsible for sciatica, disc herniation is by far the most common. In fact, some research indicates that up to 90 percent of sciatica is the result of a herniated disc in the lumbar spine.

The discs in the spine serve several functions, including giving the spine its flexibility, acting as cushions for the vertebrae, and evenly transferring the load placed on the spine from one disc to another. Disc bulging and herniation occur more frequently in the lumbar spine simply because that part of the spine supports the entire weight of the upper body as well as whatever objects you may need to pick up.

Bulging and herniated discs are almost the same, but not quite. A bulging disc is a contained disc disorder. The gel-like center of the disc (nucleus pulposus) remains “contained” within the tire-like outer wall (annulus fibrosus) of the disc but can extend the outer wall enough to press on a nearby nerve or nerve root.

A herniated disc occurs when the nucleus breaks through the annulus fibrosus. It is called a non-contained disc disorder. Whether a disc bulges or herniates, disc material can press against an adjacent nerve root and compress delicate nerve tissue and cause sciatica. This compression can occur on only one side of the sciatic nerve and cause symptoms on only one side of the body or compress it on both sides and give you symptoms on both sides of the body (bilateral sciatica).

Regardless, the consequences of a herniated disc are worse. Not only does the herniated disc cause direct compression of the nerve root against the interior of the bony spinal canal, but the disc material itself also contains an acidic, chemical irritant (hyaluronic acid) that causes nerve inflammation. To put it simply: Disc herniation is the two-for-one deal you really don’t want.

Direct Compression

Direct compression is the classic sciatica mechanism. When a disc’s jellylike nucleus bulges or bursts through the hard annulus fibrosus, that part of the disc very often presses on a nearby nerve root branching off the spinal cord and exiting the vertebra. Herniated discs in the lumbar and sacral areas of the spine will often press on one of the nerve roots that eventually combine in the buttocks to create the sciatic nerve, leading to sciatica.

Chemical Inflammation

With a herniated disc, the trouble doesn’t stop with direct compression. The soft inner layer of a disc, the nucleus, is mostly water and collagen, but releases powerful chemicals when it punches through the annulus. These chemicals cause inflammation to the immediate area, which will further irritate any nerve roots being compressed.

Technically disc degeneration is more a risk factor for herniated discs than a cause of sciatica, but it leads to sciatica so often we’d be remiss to exclude it.

Disc degeneration, or degenerative disc disease (DDD), is an extremely common and almost inevitable part of aging. Over time—years and decades—intervertebral discs undergo a drying out process called disc desiccation. The water content in the discs drop, which makes them weaker, more brittle, and more prone to herniation.

Although DDD is incredibly prevalent and almost unavoidable, there are some lifestyle modifications you can make to reduce your risk of or slow down disc degeneration, such as:

  • Practicing proper lifting mechanics
  • Keeping to a healthy weight
  • Not smoking and limiting alcohol
  • Sitting less and moving more

Spinal nerve roots branch outward from the spinal cord through passageways made of bone and ligaments called neural foramina. Nerve roots pass through these openings, join with each other to become nerves, and extend out to the rest of your body.

 

Lumbar spinal stenosis is a common cause of sciatica

When spinal stenosis develops, these foramina become narrow or clogged, and the nerves get compressed. The decrease in space within the canal is typically the result of disc herniation, but can also be caused by other issues such as:

  • Injuries to the spine, such as vertebral fractures or dislocations from trauma
  • The development of bone spurs—an overgrowth of bone—or spinal tumors
  • Thickening of the ligaments that hold the spine together

Spondylolisthesis is a disorder that most often affects the lumbar spine. It occurs when one vertebra slips forward over an adjacent vertebra. When the vertebra slips and is displaced, it presses on the nerves or nerve roots below it. This ultimately causes compression and often results in sciatica symptoms.

You’re either born with developmental spondylolisthesis or it develops during childhood. On the other hand, acquired spondylolisthesis can be caused by:

  • Parts of the spine breaking down over time (spinal degeneration)
  • Physical stress from activities like weightlifting or gymnastics
  • Trauma, such as from a car accident

“On physical examination, the patient will often complain of increased back pain when arching into extension due to irritation of the facet joints. The diagnosis can often be made with simple plain radiographs—such as an X-ray—done in the standing posture,” says Dr. Subach.

In some cases, trauma can directly cause sciatica. Examples include motor vehicle accidents (MVA), falling, and contact sports (e.g., football). The impact may injure the nerves themselves or fragments of broken bone may compress the nerves.

In addition to high-energy traumas like MVAs, other forms of trauma that can cause sciatica include pelvic fracture or hip dislocation (traction-induced sciatica) that cause nearby hamstrings to tear and irritate the sciatic nerve. It can also be the result of objects penetrating the body and cutting/tearing the nerve, such as a bullet or knife.

Piriformis syndrome is named for the piriformis muscle and the pain caused when the muscle irritates the sciatic nerve. The piriformis muscle is in the lower part of the spine, connects to the thighbone, and assists in hip rotation. The sciatic nerve runs beneath the piriformis muscle.  

The piriformis is a hip muscle that can compress the sciatic nerve when it becomes inflamed.

Piriformis syndrome can cause sciatica when the muscle spasms or becomes inflamed. Inflammation can cause the muscle swell and compress the sciatic nerve whereas the muscle spasms may impact people whose sciatic nerve runs through the muscle itself; this is because the sciatic nerve gets squeezed as the muscle contracts.

It is worth noting that piriformis syndrome may be difficult to diagnose and treat due to the lack of X-ray or MRI findings. Dr. Subach notes: “Having an experienced neurosurgeon or orthopedist perform your physical exam will make all the difference in the world, given the normal X-rays and normal MRI scans that typically accompany this cause of sciatic nerve irritation.”

Spinal tumors are abnormal growths that are either benign or malignant (cancerous). Cancerous tumors are usually metastatic, which means they have spread to the spine from cancer that had formed somewhere else in the body. Benign growths in the spine that can compress the sciatic nerve include:

  • Aneurysmal bone cysts (ABC). ABCs are not tumors—as the name dictates— but cysts that are filled with blood that tend to expand quickly.
  • Giant cell tumors (GCT). GCTs are aggressive bone tumors that usually attack bones that are close to a joint, a potentially big problem for the spine with its 364 joints.  
  • Osteoid osteomas. These tumors are found in bone, tend to be small, and do not grow larger once formed. However, they can cause new, unintended bone to form in the affected area or osteoid bone to form around the tumor itself. 

When a spinal tumor develops in the lumbar region, there is a risk for sciatica to develop as a result of nerve compression. Fortunately, spinal tumors are rare. “If your sciatic nerve pain fails to improve with medication, physical therapy, or injections, suggest an MRI scan to your pain management expert or surgeon. It can rule out an intraspinal—meaning within the spinal canal or column—cause of your pain,” says Dr. Subach.

What Are Some Less Common Causes of Sciatica?

Some lesser-known causes of sciatica can include:

  • Endometriosis, a growing of uterine tissue outside of the uterus that can accumulate in areas that surround the sciatic nerve or the sciatic nerve itself
  • Infection in the spine or spinal column that causes an abscess to form and press on the sciatic nerve or damage to the nerve itself
  • Nerve damage from diabetes
  • Shifting or growing of a fetus during pregnancy that can result in nerve compression
  • Side effects from medications

“Another common source of traumatic injury is direct damage to the peroneal nerve,” says Dr. Subach. “This often results from a knee dislocation or lower leg fracture and may present as numbness in the back of the calf or weakness in the ankle when pointing the toes toward the shin. Infrequently, it may occur in a post-operative knee or hip replacement patient. Ruling out a spinal cause in such cases is imperative.”

In addition to all of these potential causes of sciatica, features of your anatomy, your genetics, and your lifestyle can combine to make you more susceptible to sciatic nerve pain. Some of these sciatica risk factors can include:

  • Age: Getting older increases your risk of herniated discs and degenerative disc disease which, as you now know, are two of the most common causes of sciatica
  • Obesity: Carrying an unhealthy amount of extra weight stress the spine and puts more pressure on your discs, which can lead to herniation or other damage
  • Jobs and activities: Some jobs are strenuous and physical, involving lots of lifting and twisting. Lifting and twisting unsafely can be big contributors to sciatica risk. Conversely, other jobs have you sitting for too long, which can also stress your discs, especially if that sitting leads to weakened core muscles and, therefore, less protection for your spine and its discs.
  • Spine injury: Previous injury can weaken discs and make them more susceptible to herniation and damage.

How Is Sciatica Treated?

Treating sciatica can often be done through self-care at home. Doing things like applying ice packs, taking over-the-counter pain relievers/inflammation reducers, and gentle stretches help to reduce inflammation in and around the sciatic nerve or whatever is compressing it to alleviate symptoms.

Your doctor also may:

  • Offer prescription medication, such as a muscle relaxant or painkiller
  • Recommend physical therapy that will help reduce pressure on the nerve
  • Advise getting spinal injections near the affected nerve to reduce inflammation
  • Suggest alternative techniques to relieve symptoms, such as acupuncture or yoga 

Surgery for sciatica is rare, but the most common procedures are a microdiscectomy, which clears out part of a herniated disc, or laminectomy that removes part of a vertebra to make more room in the spinal canal.

There you have it. Understanding what’s causing your sciatica leads to understanding how to treat it. Getting a diagnosis and shedding light on your sciatica cause is the first step in feeling better.  

FAQs

What causes sciatica to flare up?

Sciatica can be caused by any number of issues that can pinch a sciatic nerve or nerve root. This includes bulging discs, spinal stenosis or injury to the spine. Often a patient may “overdo” a certain mildly strenuous activity, such as gardening or lifting boxes. Limiting activity, ice to the low back area, and taking an over-the-counter anti-inflammatory agent will generally allow the symptoms to improve. If you continue to experience pain after a few days, call your doctor.

What causes sciatic pain during pregnancy?

During pregnancy, a bundle of nerves known as the lumbosacral plexus can be pressed between the fetus and pelvic bones. Additionally, spending a prolonged amount of time in the lithotomy position (having hips and knees flexed and supported by stirrups) can also cause sciatica.

Which vertebrae cause sciatica?

The origins of sciatic pain can begin as high as the L4 (lumbar) vertebrae and as low as S1 (sacrum) vertebrae. Each vertebra—including L5—has a corresponding nerve root that feeds to the sciatic nerve; depending on which root is affected, symptoms may vary slightly in where they radiate to.

Can stress and anxiety cause sciatica?

There is some research that suggests that when you experience anxiety, the brain denies the nerves in the lower back oxygen, resulting in sciatic symptoms. In addition to this, cortisol (a hormone produced when you’re stressed) may make sciatica worse and/or cause it to last longer.

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