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Is Your Sciatica Coming From Your Spine or Your SI Joint?

If you have pain radiating down your leg, you may immediately think: “I have a pinched nerve in my back.” But sacroiliac (SI) joint dysfunction can also cause pain that radiates down the leg. So, how do you tell the difference? 

First, it’s important to understand that sciatica is not a diagnosis: it’s a symptom related to an underlying condition. Sciatica is the sensation of pain, tingling, weakness, and/or numbness in the lower extremities that is typically caused by compression or irritation of a spinal nerve(s) or of the sciatic nerve itself (see diagram). Usually, the nerve compression or irritation occurs in the lumbar spine.

The tricky thing is, the real source of the pain might be something else: your SI joint.

Start here to better understand your symptoms and what to do about them:

Nerve Compression or Irritation from the Spine Versus Nerve Irritation Related to the SI joint:

Even if you’ve determined that you have sciatica, the cause could be nerve irritation or compression in the spine OR you may have an SI joint problem OR a combination of both. The L5 and S1 spinal nerves are located very close to the SI joint, and SI joint dysfunction could result in irritation of those nearby nerves.

How can you be certain what’s causing the pain?

The only way to truly know what’s going on is to see your doctor and describe what you are feeling and experiencing. Your doctor will likely ask many questions, ask you to point to the source of your pain, and perform a physical exam.

Sciatic anterior

Here are a few subtle differences that he or she may be looking for:

Sciatica and other symptoms 
from Nerve Compression in the Spine
Sciatica and other symptoms 
from the SI Joint
  • Pain that starts in the lower back and goes down one leg (the leg pain is usually greater than the low back pain)
  • Lower back pain (below L5) that is off to one side that you can typically point to
  • Pelvis/buttock pain
  • Hip/groin pain
  • Pain, weakness, and/or numbness or a tingling sensation radiating to the calf, foot, or toes along the back of your buttock, thigh, and calf. You may have actual weakness and/or numbness as a result of compressed nerves.
  • Pain can be mild to excruciating; it may feel like an “electric shock”
  • Sensation in lower extremity: pain, numbness, tingling, weakness. Upon exam, patients do not usually have true weakness or numbness.
  • Typically, the pain stays above the knee, but can radiate down the leg to the calf or foot.
  • Severe cases may result in significant leg weakness
  • (Weakness, numbness, and reflex changes are called radiculopathy.)
  • Feeling of pain and leg instability (buckling, giving way) when standing.
  • The leg isn’t actually weak; the leg gives way because of the severe pain you may experience when the SI joint is loaded.
  • Sitting for a long time can make symptoms worse.
  • Pain going from sitting to standing. Unable to sit for long periods of time or sitting or sleeping on one side due to the pain. (Disturbed sitting and sleeping patterns.)
  • Typically felt on one side.
  • Can be on one or both sides, although typically on one side.

It’s rare for someone with sciatica from an SI joint problem to have real numbness, weakness, or reflex changes. This is because there is rarely a physical compression of the nerve. The L5 and/or S1 nerves are irritated (called radiculitis) when they cross near the SI joint, but these nerves are not compressed.

Your radiating leg pain (sciatica) can be from your spine or from your SI joint. However, it is possible to be diagnosed with problems in both areas. That’s why it’s so important to visit your doctor to truly determine what is causing your low back or leg pain.

SI Joint and Sciatica Definitions

Let’s back up a step and make sure we fully understand the definitions of sciatica and SI joint dysfunction.

What Is Sciatica?

Sciatica is a symptom (radiating leg pain) caused by a problem with the spinal nerve(s) or sciatic nerve, such as compression or irritation, which sends signals of pain, numbness, tingling, or weakness. The sciatic nerve is a made up of several nerves from your lower spine; it extends down the back of your leg to the bottom of your foot. You have one on each side. Sometimes, the compression in the spine affects nerves on both the left and right sides of the body.

The sciatic nerve carries nerve signals down to the muscles and sensation signals up to the spinal cord. These signals tell your muscles to move; when these signals are disrupted, this is why you might sometimes feel weakness or buckling in the knee.

What Is SI Joint Dysfunction?

Sacroiliac (SI) joint dysfunction is caused by trauma or degeneration of the SI joint. The SI joint is where your iliac bone (pelvis) connects to the sacrum (lowest part of the spine above the tailbone).

The SI joint is responsible for transferring the weight from your upper body to your pelvis and legs. Pain caused by SI joint dysfunction can be felt in the lower back or spine, buttocks, pelvis, groin, and sometimes in the legs, which makes it seem like the cause could be nerve compression in the spine.

The L5 and S1 nerves are near the SI joint and studies have shown that SI joint dysfunction can cause pain and other symptoms in the distribution of these nerves.

The SI joint is separate from the sciatic or spinal nerve(s); however, the SI joint can cause sciatica-like symptoms.

Underlying Causes of Sciatica Pain and SI Joint Pain

Oftentimes, it’s difficult to pinpoint the exact cause of pain. Nerve compression in the spine and SI joint dysfunction are two areas that often cause pain running down the back of the leg.

Spine Problems that Can Result in Sciatica

  • A bulging, ruptured, or herniated disc in the spine
  • Central spinal stenosis or when your central spinal canal is constricted
  • Foraminal stenosis, when the openings where the nerves leave the spine become tight
  • Spondylolisthesis (or segmental instability), when one vertebra slips forward in the lower back
  • Facet arthropathy, a wearing down of the cartilage between the facet joints in the back of the spine
  • Injury or infection
  • Nutritional deficiencies and genetic problems (less common)

SI Joint Dysfunction: Potential Causes

  • Trauma to the SI joint from a fall, car accident, or giving birth
  • Degeneration of the SI joint

Both situations can be acute (lasting a couple weeks and resolving on its own) or chronic (lasting a very long time).

People with chronic SI joint dysfunction can suffer with the pain for years before they receive the correct diagnosis and treatment.

If your pain has lasted more than a couple weeks or is impacting your daily life, see a doctor right away.

Sciatic posterior

Testing to Determine the Source of Your Leg or Lower Back Pain

Your doctor will likely ask many questions, such as when the pain started, how long it lasts, and what causes it to get worse or better. Answers to these questions will provide clues to which tests you should get first.

For example, if your pain started after a fall on the buttocks or if it extends to the groin area, that might be a clue that it’s SI-joint-related, and you may require physical examination including provocative tests.

Provocative tests help determine whether the pain is caused by the SI joint. A diagnostic injection can help confirm diagnosis. If you are experiencing true muscle weakness, this could indicate that you have a pinched nerve in the spine. When nerves are compressed/irritated in the spine, patients will frequently have a positive passive straight leg raising test.

Your doctor will also likely rule out potential causes of nerve compression in the spine, such as a bulging disc, with an MRI of the spine and other radiological and laboratory testing.

Sometimes patients are misdiagnosed, like in the case of Keith, who was diagnosed with a pinched nerve in the spine but in reality, had SI joint dysfunction. The pain was coming from his SI joint. See Keith's Sciatica from SI Joint Pain Story.

Treatments to Relieve the Pain

Conservative therapies to treat sciatica from both the spine or the SI joint may include therapeutic injections of steroids, which may offer temporary relief. For sciatica related to the spine, the injection will be targeted in the lumbar spine at the site of the nerve compression. For sciatica related to SI joint dysfunction, the injection will be targeted in the SI joint.

Treatment of spinal conditions may include medications, physical therapy (including exercises specific for sciatic pain), and in extreme cases, surgery to remove the pressure from the pinched nerve(s) in the spine.

SI joint dysfunction treatments also include medications, physical therapy and other non-surgical treatments, and if non-surgical treatments no longer work, minimally invasive SI joint fusion may be an option.

If you suspect your lower back and leg pain is caused by your sacroiliac joint or your spine, visit your doctor with a list of symptoms, including when the pain started, and what makes it worse. If it turns out you need an SI joint specialist, you can find one in your area here.

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More Related Resources

More links and information regarding the diagnosis and treatment of SI Joint Pain:

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