The sacroiliac joint, also called the “SI joint,” is the joint at the back of your hip where your pelvis (iliac bone) meets your tailbone (sacrum). You have two SI joints, one on either side of your tailbone. When you experience SI joint pain, it’s called sacroiliac joint dysfunction, or sacroiliitis.
Sacroiliac joint dysfunction can be caused by inflammation, arthritis, or infection.
Sacral insufficiency fractures are another condition that may be causing sacrum pain. These are stress fractures that occur when the tailbone has become weakened, usually from osteoporosis.
Both SI joint problems and sacral insufficiency fractures can be difficult to diagnose and are often missed. This is because symptoms often mimic low back and hip pain.
Sacroiliac joint dysfunction is usually treated with physical therapy, medication, and injections of anti-inflammatory drugs.
Sacroiliac joint problems, including insufficiency fractures, usually cause pain in the buttocks or low back that may shoot down the back of your thighs. The pain is usually worse when you put weight on your legs, especially if you tend to shift your weight to one leg more than the other. Climbing stairs, running, and standing or sitting for too long can cause pain.
- Pain in the back of the hip and buttocks
- Pain when sitting or standing too long
- Pain when shifting your weight to one leg
Other symptoms you may have
- Radiating pain at the back of the thigh
- Difficulty climbing stairs
Pregnant women are at risk for SI joint problems because changes in hormone levels can weaken SI ligaments, which support the SI joints. This may lead to excess motion of the SI joint, which then places stress on the joints.
Although rare, it’s possible for the SI joints to become infected, usually from an infection somewhere else in the body that spreads through the blood.
Sacral insufficiency fractures often happen in people with a history of osteoporosis. This is because the bones are weaker than normal and may not be able to tolerate repetitive stress.
- Prior injury to the pelvis or SI joints
- Inflammatory arthritis (particularly ankylosing spondylitis)
- Infection (usually spreads from somewhere else in the body)
- Osteoporosis (for insufficiency fractures)
- Prior back fusion surgery
The SI joints are stabilized by some of the strongest ligaments in the human body. As a result, not much motion takes place at these joints, and they are rarely a source of pain. However, some patients can develop inflammation or dysfunction of the SI joints that lead to back pain, buttock pain, and pain at the back of the thighs. —Dr. Schwartz
Most cases of SI dysfunction can be treated at home with rest, ice, and over-the-counter anti-inflammatory medications. If your pain doesn’t improve after 2 to 4 weeks of home treatment, see your doctor.
Because SI joint problems and low back problems can have similar symptoms, like a herniated disc, you may need several tests to rule those out. These include:
- Physical exam tests that put pressure on the SI joints to see if they cause pain.
- X-rays of your pelvis to look for arthritis in the SI joints.
- X-rays of your lumbar spine (low back) to rule out arthritis in your back.
- An MRI of your pelvis to check for inflammation of the SI joint or sacral insufficiency fractures that aren’t easily seen on X-rays.
If you have severe pain at the back of the hip and buttocks along with a fever, it could mean you have an infection in the SI joint. While this is a rare problem, go to the ER. Treatment requires antibiotics (usually through an IV).
Treatment of sacroiliitis depends on the cause. For people who have osteoarthritis of the joint, you should avoid activities that cause pain. You can also apply ice or heat, and take anti-inflammatory drugs (NSAIDs, like ibuprofen).
Your doctor may recommend physical therapy if your symptoms don’t improve after 4 to 6 weeks.
If the pain doesn’t improve, cortisone (steroid) injections in the SI joints can be helpful. In rare cases, surgery may be performed to fuse the tailbone to the pelvic bone.
If SI joint inflammation is caused by ankylosing spondylitis, your doctor may prescribe more powerful medications to reduce inflammation, such as adalimumab (Humira), etanercept (Enbrel), and infliximab (Remicade).
If you’re pregnant, the joint pain will usually go away after your delivery.
Like many controversial and uncommon diagnoses, there is a lot of misinformation on the Internet. While treatments like physical therapy and chiropractic care can help, overly aggressive manipulation can cause pain. No amount of forceful pushing will “pop” SI joints back into place. Websites may also make misleading or untrue claims about the success rates of SI joint fusion surgery or tout “minimally invasive” procedures that have not been proven by rigorous scientific study. —Dr. Schwartz
- Over-the-counter NSAIDs, such as ibuprofen (Motrin) and naproxen (Aleve).
- Prescription NSAIDs
- Acetaminophen (Tylenol)
- Cortisone injections into the SI joints
- Medications to reduce inflammation, such as adalimumab (Humira), etanercept (Enbrel), and infliximab (Remicade)
- Osteoporosis medications (for insufficiency fractures)
In rare cases, surgery may be recommended to fuse the tailbone to the pelvic bone. Screws are inserted across the joint to eliminate any motion between the tailbone and pelvis.
SI joint fusion surgery is somewhat controversial. Some studies show excellent pain relief and others show a less successful outcome. Surgery should only be considered when all other potential causes of pain have been ruled out and you have tried other non-surgical treatment options for more than a year.
Make a follow up appointment with your doctor after 4 to 6 weeks of treatments, like medications and physical therapy. If your pain doesn’t improve, your doctor may recommend an MRI to look for other conditions.
People who have an SI joint cortisone injection may follow up after 2 to 3 weeks to discuss if the shot was effective and decide on next steps if it wasn’t.
If you have an insufficiency fracture, you may need X-rays 6 to 8 weeks later to make sure the fracture is healing correctly.
- Avoid activities that cause pain in the SI joints
- Manage ankylosing spondylitis symptoms
- Get tested and treat possible osteoporosis