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 joints are 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 sacroiliac joints are located where the sacrum and ilium meet in the lower back. 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. They act as a shock absorber and reduce the pressure that movement puts on your spine.

The bones of the SI joints are uneven and fit together like a puzzle. These edges help them stay in alignment. 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 remaining upright and even for giving birth.

The joint bones themselves are also lined with a protective layer of cartilage. Spaces between the bones of the SI joints are filled with fluid, which provides lubrication. These spaces are filled with free nerve endings, which send pain signals to the brain.

When the bones in the SI joint are out of alignment, or when the cartilage breaks down and causes the bones to touch, it can be painful.

Inflammation of one or both SI joints is called sacroiliac joint dysfunction, or sacroiliitis. Sacroiliitis can be caused by a number of conditions, including the following.

Osteoarthritis

Years of stress on your joints 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 an autoimmune disease that causes 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.

The weight gain necessary for pregnancy combined with the the increased motion of the body adapting to the weight of the baby can lead to SI joint pain. Pregnant people 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 such as a leg length discrepancy, a fused knee, hip, or ankle, or favoring one leg because of pain. Correcting these problems may resolve your SI joint pain.

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

Some cases of SI joint pain aren’t preventable, as they’re caused by other chronic conditions.

Still, just as staying limber and active can help stave off other joint pains, you may be able to slow the progression of SI joint pain by exercising and making healthy lifestyle choices.

The best prevention is to maintain a lower weight within your comfort range.

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.

The symptoms of an inflamed SI joint are also very similar to those associated with conditions like sciatica, bulging discs, and arthritis of the hip.

Your doctor may take use the following strategies to diagnose SI joint problems:

  • A physical examination. Your doctor will ask you to move and stretch in specific ways. This can help them pinpoint the source of your pain.
  • Numbing drugs. If injecting a numbing drug, such as lidocaine, into the SI joint causes the pain to go away after a short period of time, you most likely have an SI joint problem.
  • Imaging tests. This includes 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 way to try and alleviate pain is by using cold packs. Alternatively, when the pain is more manageable, apply heat with a heating pad or heat wrap, or a soak in a warm bath. Both heat and cold can ease joint pain.

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 fusion is effective at reducing pain, but does slightly limit the joint’s range of movement.

SI joint pain can be short-term, especially when caused by pregnancy, injury, or strain. With chronic conditions, including AS and osteoarthritis, pain may come and go.

But in most cases, pain can be relieved significantly with treatment.