You may experience sacroiliac (SI) joint pain as a sharp, stabbing pain that radiates from your hips and pelvis, up to the lower back, and down to the thighs. Sometimes it may feel numb or tingly, or as if your legs are about to buckle.

The SI joint is to blame in 15 to 30 percent of people with chronic lower back pain.

About 80 percent of adults in the United States will experience lower back pain during their lives. Lower back pain is a leading cause of missed workdays, and the most common cause of job-related disability.

Your SI joints are located where the sacrum and ilium meet. The sacrum is the triangle-shaped bone near the bottom of your spine, just above your coccyx, or tailbone. The ilium, one of the three bones that make up your hip bones, is the uppermost point of your pelvis.

The SI joints support the weight of your body, distributing it across the pelvis. This acts as a shock absorber and reduces the pressure on your spine.

The bones of the SI joints are jagged. These jagged edges help them stay in alignment. Spaces between the bones of the SI joints are filled with fluid, which provides lubrication. These spaces are also filled with free nerve endings, which send pain signals to the brain. When the bones in the SI joint become out of alignment, it can be painful.

All of the bones in the SI joints are connected by muscles and extra-strong ligaments, which add stability and allow for limited movement. Though minimal, this movement is necessary for you to remain upright and for women to give birth.

Inflammation of one or both SI joints is called sacroiliac joint dysfunction, or sacroiliitis. Sacroiliitis may be caused by SI joint dysfunction. This is a general term that encompasses a number of conditions, including the following.

Osteoarthritis

Years of stress on the SI joint can eventually wear down the cartilage and lead to osteoarthritis. Associated with aging, osteoarthritis can affect the SI joint, spine, and other joints throughout the body.

Ankylosing spondylitis

Ankylosing spondylitis (AS) is a type of inflammatory arthritis that affects the vertebrae and joints of the spine. In addition to causing pain, severe cases of AS can cause new bone growth that fuses the joints in the spine.

Although AS primarily affects SI joints, it can also cause inflammation in other joints and, more rarely, organs and eyes. AS is a chronic disease. It may cause intermittent episodes of mild pain, or more severe ongoing pain. This disease is diagnosed most frequently in young men.

Gout

Gout, or gouty arthritis, can occur if your body has high levels of uric acid. This disease is characterized by joint pain, which can be severe. Although gout almost always affects the large toe first, all joints can be affected, including the SI joint.

Injury

SI joints can be injured by trauma, such as injuries resulting from falls and car accidents.

Pregnancy

Relaxin, a hormone released during pregnancy, makes the SI joints more elastic. This enables the pelvis to widen to accommodate the birth of a baby. It also makes the joints less stable. Combined with weight gain and the weight of the baby, this often leads to SI joint pain. Women who experience this are more prone to getting arthritis in the SI joints, a risk that increases with each pregnancy.

Walking patterns

Walking abnormally can cause SI joint dysfunction. You may walk abnormally because of issues like having one leg shorter than the other or favoring one leg because of pain. Correcting these problems may resolve your SI joint pain.

Some women may walk abnormally while they’re pregnant. Once they give birth and resume walking normally, their SI joint pain may go away.

Each person experiences symptoms of SI joint disorders somewhat differently. Common symptoms include:

  • pain in the lower back
  • pain in the buttocks, hips, and pelvis
  • pain in the groin
  • pain limited to just one of the SI joints
  • increased pain when standing up from a sitting position
  • stiffness or a burning sensation in the pelvis
  • numbness
  • weakness
  • pain radiating down into the thighs and upper legs
  • feeling like your legs may buckle and not support your body

SI joint problems can be difficult to diagnose. The joints are located deep in your body, making it difficult for your doctor to examine or test their motion. Often, damage to the joints doesn’t show up on imaging tests such as X-rays, MRIs, or CT scans. And the symptoms are very similar to conditions like sciatica, bulging disks, and arthritis of the hip.

Your doctor may take the following steps in order to diagnose SI joint problems:

  • An examination during which they ask you to move and stretch in specific ways. This can help them pinpoint the source of your pain.
  • Injecting a numbing drug, such as lidocaine, into the SI joint. If the pain goes away after a short period of time, this indicates that you most likely have an SI joint problem.
  • Imaging tests, such as X-rays, MRIs, and CT scans.

Therapy, exercise, and self-care

Physical therapy, low-impact exercise like yoga, and massage can help stabilize and strengthen the SI joints and ease pain.

Another tip is to use cold packs to alleviate the pain. When the pain is more manageable, apply heat with a heating pad or heat wrap, or a soak in a warm bath.

You can also wear a sacroiliac belt to help support the SI joint, which may help ease your pain.

Medication and nonsurgical therapies

If your SI joint pain can’t be managed with physical therapy, exercise, and self-care, or if it’s caused by a chronic condition like AS, your doctor may recommend medication and nonsurgical therapies. These can include:

  • anti-inflammatory medications, including nonsteroidal, anti-inflammatory drugs (NSAIDs) such as aspirin, ibuprofen, and naproxen
  • muscle relaxants
  • oral steroids, for short-term use only
  • tumor necrosis factor inhibitors (TNF inhibitors) to treat AS
  • corticosteroid injections into the joint
  • radiofrequency ablation, which uses energy to deactivate the nerves that are causing your pain

Surgery

Surgery is the considered the last resort. With sacroiliac joint fusion surgery, small plates and screws hold the bones in the SI joint together so the bones fuse, or grow together. Your doctor may suggest this surgery if the pain is chronic and the combination of physical therapy, medications, or minimally invasive interventions hasn’t been effective.

SI joint pain can be short-term, especially when caused by pregnancy, injury, or strain. Other conditions, including AS and osteoarthritis, are chronic. But in most cases, pain can be relieved significantly with treatment.

Some causes of SI joint pain aren’t preventable. But you may be able to slow the progression of these conditions by exercising and making healthy lifestyle choices.