About 80% of adults will have low back pain at some point in their lives, according to the National Institutes of Health. Some episodes are caused by specific events, like a sprain, traumatic injury or herniated disc. But others may have more subtle origins—like strained ligaments or the gradual wearing down of cartilage around the joints.
Problems with the sacroiliac joint—the junction at the base of the spine connecting the backbone to the hip bones—often fall under that second category, says Dr. David Borenstein, rheumatologist and clinical professor of medicine at George Washington University. Also called the SI joint, it’s a common cause of low back pain, but not always an obvious one.
The body has two sacroiliac joints, one on each side of the spine. Each joint’s role is to act as a shock absorber and support the weight of the upper body, while remaining relatively stable. “It’s not like the knee or elbow that bends back and forth,” says Dr. Alice Chen, a physiatrist at the Hospital for Special Surgery in New York City. “It’s a joint that doesn’t have much motion—or at least it’s not supposed to.”
Women tend to have more SI joint-related pain than men, since their joints are naturally a bit looser. The SI joint is often associated with premenstrual syndrome–related back pain, as well as back pain during and after pregnancy, says Chen. (Ligaments around the pelvis stretch to prepare for birth, putting extra stress on the joints and the nerves around them.)
SI joint pain can also happen to men and women as a result of a physical trauma or, very rarely, a bacterial infection. But most often, it’s caused by tight or weak muscles surrounding the joint, says Borenstein. If those issues aren’t addressed, they can wear down the SI joint’s connective tissue and cause arthritis over time.
Pain related to the SI joint is most noticeable in the lower back, but it can also radiate into one hip, leg or glute. The pain may worsen when bending, running, climbing stairs, jumping or after sitting for long periods of time.
Treatment for SI joint-related issues usually involves anti-inflammatory drugs and physical therapy that targets the muscles around the joint. “Strengthening the buttock muscles and the low back and core muscles can be helpful in stabilizing the sacroiliac joint,” says Borenstein, “especially in situations where it may have been strained.”
In severe cases, steroid injections or radiofrequency ablation—the use of an electric current to numb a painful joint—can also provide short-term relief.
“It’s really a condition that’s tricky to treat,” says Chen. A back specialist is the best person to diagnose and treat pain related to the SI joint, she says, and to rule out other injuries.