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Published on April 04, 2019

Hope for hard-to-treat back pain

Doctors can identify most causes of back pain with physical exams and tests, but some cases are more puzzling.

“A patient might come to us with back pain, we’ll do an MRI of his or her spine, and we don’t see anything that explains their symptoms,” said Paul Houle, MD, FAANS, a neurological surgeon at Cape Cod Hospital. What’s more, sometimes when doctors do identify a suspicious-looking spinal abnormality, surgery to correct it fails to relieve a patient’s back pain.

For many such patients with mysterious, hard-to-pinpoint symptoms, the trouble turns out to originate in the very lowest region of the back, where the spine meets the pelvis, known as the sacroiliac (SI) joints. Studies suggest that 15 to 30 percent of low back pain arises in the SI joints. The pain radiates upward, into the lower back, and sometimes downward, into the legs.

Doctors have known for some time that dysfunction in the SI joints can trigger back pain, but until recently had little besides medication to offer patients debilitated by the problem. However, in recent years, doctors at Cape Cod Hospital and other medical centers have developed and refined a surgical technique known as sacroiliac joint fusion that can bring rapid relief.

Support the Upper Body

To understand how fusion surgery eases pain arising from the SI joints, it helps to recall a bit of high school anatomy. Humans have two triangle-shaped hip bones, and the upper portion of each one is called the ilium. Each ilium connects to the sacrum, a shield-shaped bone that sits just above the coccyx (better known as the tailbone), to form the two SI joints. The SI joints support the upper body, but don’t hinge much, like your knee or elbow joints.

However, these joints move enough to create the pelvic movements necessary for women to give birth. The stress childbirth places on the SI joints explains why women are more at risk than men for this form of back pain. Also, people who have had lumbar joints surgically fused to treat low back pain sometimes develop SI joint problems. That’s because fused joints transfer stress onto adjacent joints, irritating nerve endings and causing pain.

“But if you stabilize that joint, the pain goes away because you’re no longer stressing those nerve endings,” explained Dr. Houle, whose practice, Cape Cod Healthcare Neurosurgery, is located on North Street in Hyannis.

When he suspects a patient’s low back pain is caused by instability in an SI joint, he sends him or her to the Cape Cod Hospital Pain Center for cortisone injections into the joint. If the injections bring temporary relief, the patient’s back pain is likely arising from the SI joint.

An Outpatient Procedure

An operation to fuse an SI joint takes about a half hour and is usually performed as an outpatient procedure. Dr. Houle begins by using the O-arm device to acquire a three-dimensional image of the SI joints, which he uses to plan positioning of the stabilizing implants. A small incision is made in the skin, through which a delicate drill is used to produce two holes that pass through the pelvis and into the sacrum. Next, tubular cages filled with donor bone from a cadaver are inserted into the holes.

“That provides immediate stability of the joint,” said Dr. Houle. Over time, the bone grows through the cages and fuses the two bones.

“A lot of patients report that within a couple of days that horrible pain that brought them to my office is gone,” he said, noting that discomfort from surgery fades over a few weeks. After the procedure, patients are encouraged to participate in a physical therapy program designed to promote healthier functioning of the SI joints.