Dysfunction in the sacroiliac joint, also called the SI joint, can sometimes cause lower back and/or leg pain. Leg pain from sacroiliac joint dysfunction can be particularly difficult to differentiate from radiating leg pain caused by a lumbar disc herniation(sciatica) as they can feel quite similar.
For decades, the sacroiliac joint was suspected as a common cause of low back and/or leg pain, although difficulty in accurate diagnostic testing left many in the medical profession skeptical. Today it is estimated that the sacroiliac joint is responsible for 15% to 30% of lower back pain cases.
Anatomy of the Sacroiliac Joint
The sacroiliac joint connects the hip bones (iliac crests) to the sacrum, the triangular bone between the lumbar spine and the tailbone (coccyx). The primary function of the sacroiliac joints is to absorb shock between the upper body and the pelvis and legs.
The sacroiliac joint typically has little motion. Small movements at the joint help with shock absorption and forward/backward bending. The joint is reinforced by strong ligaments surrounding it, some of which extend across the joint in the back of the pelvis. This network of soft tissues provides support, limits movement at the joint, and assists with absorbing pressure.
Other muscles that support sacroiliac joint function include the gluteus maximus and the piriformis muscle.
Sources of Sacroiliac Joint Dysfunction
The primary mechanisms of SI joint dysfunction include:
Too much movement (hypermobility or instability) in the sacroiliac joint can cause the pelvis to feel unstable and lead to pain. Pain from too much motion is typically felt in the lower back and/or hip, and may radiate into the groin area.
Too little movement (hypomobility or fixation) can cause muscle tension, pain, and may inhibit mobility. Pain is typically felt on one side of the low back or buttocks, and can radiate down the back of leg (similar to sciatica pain).
Inflammation of the sacroiliac joint (sacroiliitis) can also produce pelvic pain and stiffness. Sacroiliac joint dysfunction may cause inflammation, or inflammation may occur with normal function of the joint from an infection, rheumatoid condition, or other cause.
Sacroiliac joint dysfunction is more common in young and middle-aged women. Women who are pregnant or have recently given birth may be more susceptible to sacroiliac joint pain.2
Symptoms experienced with sacroiliac joint dysfunction commonly include:
Lower back pain that feels dull, aching, and can range from mild to severe. Lower back pain is typically felt only on one side, but in some cases may be felt on both sides.
Pain that spreads to the hips, buttocks, and/or groin. One of the most common areas to feel SI joint pain is in the buttocks and upper back or side of the thigh. Pain is typically felt only on one side, but may be felt on both sides.
Sciatic-like pain in the buttocks and/or backs of the thighs that feels hot, sharp, and stabbing and may include numbness and tingling. Sciatic-like pain from sacroiliac joint dysfunction rarely extends below the knee.
Stiffness and reduced range-of-motion in the lower back, hips, pelvis, and groin, which may cause difficulty with movements such as walking up stairs or bending at the waist.
Worsened pain when putting added pressure on the sacroiliac joint, such as climbing stairs, running or jogging,and lying or putting weight on one side.
Instability in the pelvis and/or lower back, which may cause the pelvis to feel like it will buckle or give way when standing, walking, or moving from standing to sitting.
Aggravation of the sacroiliac joint can commonly result in inflammation, also called sacroiliitis. This condition may be the primary cause of pain, stiffness, and other symptoms.
Causes and Risk Factors for Sacroiliac Joint Dysfunction
Certain factors can raise the risk of developing sacroiliac dysfunction and pain, including:
Gait issues, such as leg length discrepancy or scoliosis, which can place uneven pressure on one side of the pelvis, causing wear-and-tear on the SI joint and an increased risk of pain.
Pregnancy or recent childbirth can commonly cause sacroiliac joint pain in women due to weight gain, hormonal changes causing ligaments in the SI joint to relax (hypermobility), and pelvic changes associated with childbirth. For some women, ligaments may remain loose after childbirth and cause sacroiliac joint pain and instability to continue.
Prior lower back surgery, which can displace pressure to the sacroiliac joint. One study found that sacroiliac joint pain tends to be more common following a fusion surgery than a discectomy.3 The same study found that multi-level surgery was more likely to cause sacroiliac joint pain than a single-level procedure. Sacroiliac joint pain has also been reported following hip joint replacement surgery and bone grafts taken from the iliac bone (the “wings” of the pelvis).
Activities that place repeated stress on the joint, such as contact sports, regular heavy lifting, or labor-intensive jobs. If pelvic and/or low back muscles are unconditioned, stress from prolonged sitting or standing may also contribute to SI joint pain.
There is no single approach to managing SI joint pain that will work for everyone. A combination of nonsurgical treatments is usually necessary for effective pain relief. Additionally, a period of trial-and-error may be needed to find treatments that address specific symptoms.
Physical Therapy for Sacroiliac Joint Pain
Physical therapy to rehabilitate the sacroiliac joint typically includes:
Stretching to reduce muscle tension and spasms in the lower back, hips, and pelvis, including the piriformis, gluteus maximus, and hamstring muscles. Tension in these muscles caused by sacroiliac joint dysfunction can be the primary cause of pain.
Strengthening exercises to better support the sacroiliac joint and pelvis/lower back. Better support for the joint can come from strengthening the abdominal muscles, lateral trunk muscles, and low back muscles.
Aerobic exercise. Any well-rounded exercise program should include aerobic exercise to elevate blood flow and bring nutrients and oxygen to damaged tissues, which can facilitate the healing process. Low-impact aerobics may be needed for SI joint dysfunction to minimize pain from exercise, and can include stationary cycling, running on an elliptical, or water aerobics.
Exercises for sacroiliac joint dysfunction are designed to gently return the joint to normal function and mobility, in turn reducing pain and other symptoms. Exercises may be individualized and vary from case to case.
The standard surgery used to address SI joint pain is sacroiliac joint fusion. The goal of this procedure is to completely eliminate movement at the sacroiliac joint by grafting together the ilium and sacrum.
Sacroiliac fusion involves the use of implanted screws or rods, as well as a possible bone graft across the joint. Minimally-invasive procedures have been developed in recent years that improve outcomes in pain and disability, and reduce recovery time.
Deciding on Sacroiliac Joint Fusion
Sacroiliac joint fusion is only recommended once nonsurgical treatments have been tried for at least 8 to 12 weeks and are generally ineffective. In most cases, nonsurgical treatments are tried for several months before surgery is advised.
The biggest risk of sacroiliac joint fusion is the possibility that surgery won’t alleviate pain, and/or that fusion of the joint will be unsuccessful. There is also the possibility that the fused sacroiliac joint will displace pressure typically absorbed in the pelvis to the lower spine, creating pain and pressure in the lower back (called adjacent segment disease). This complication has been reported in about 5% of sacroiliac joint fusion patients within 6 months of surgery.
Sacroiliac Joint Fusion Procedure
There are two surgical systems used for sacroiliac joint fusion, which include the implants that fuse the joint as well as other tools needed to perform the surgery. All minimally-invasive sacroiliac joint fusion procedures consist of the following:
Under general anesthesia, a small incision is made over the lower back and muscles are gently moved to the side.
A device is used to drill a small hole through the ilium and access the joint.
The sacroiliac joint is cleared of ligaments and muscles, and a bone graft and surgical implants are put in place across the joint to encourage bone growth.
Muscles are put back in place, and the surgical site is closed using standard sutures.
A hospital stay of 1 to 2 nights may be needed following surgery.
Recovery from sacroiliac joint fusion typically includes a combination of pain medications, physical therapy, and at-home treatments such as applying heat and ice. Additionally, a pelvic brace may be prescribed to stabilize the pelvis and limit painful movements during healing. The recovery period for sacroiliac joint fusion typically lasts between 3 and 6 months.