SI Joint Fusion is Highly Successful in Most People Who Respond to an SI Joint Block

Peer Reviewed

Sacroiliac (SI) joint fusion using the iFuse Implant System is highly successful in people with SI joint dysfunction who have a physical exam pointing to the SI joint and experience pain relief during a diagnostic SI joint block (injection of a numbing agent into the SI joint), according to a study in the International Journal of Spine Surgery. The degree of response to the SI joint block in this study (50%-75% pain relief compared to >75% pain relief) did not predict the outcome of fusion surgery.

painful sacroiliac jointsThe degree of response to the SI joint block in this study did not predict the outcome of fusion surgery. Photo Source: findings by suggest that “the learning bar may be set too high in selecting patients for SI joint fusion” using current criteria of ≥75% pain relief from 2 consecutive injections, commented Steven R. Garfin, MD, Distinguished Professor and Chair of the Department of Orthopaedic Surgery at the University of California, San Diego, and member of the SpineUniverse editorial board.

Diagnosis of SI joint dysfunction is typically is based in part on whether the pain is relieved by an SI joint block. In this study, the researchers studied whether the degree of pain relief with SI joint block could predict which people had successful outcomes from SI joint fusion.

The study, which was sponsored by SI-BONE, included 320 people with SI joint dysfunction diagnosed by history, physical exam, and SI joint block. All the participants had at least a 50% decrease in pain following SI joint block.

The fusions were performed using the iFuse Implant System, a device made of triangular-shaped titanium rods that attached horizontally across the bones that make up the painful SI joint—the sacrum and part of the pelvis known as the ilium. The device is placed using small cuts in the skin to limit damage to surrounding tissue (known as minimally invasive surgery) as opposed to open surgery that uses larger cuts in the skin.

High Success Rate From SI Joint Fusion

The iFuse device successfully reduced pain in 77% to 85% of people and improved disability level in 59.4% to 75.0%, regardless of their response to the SI joint block. In fact, the level of improvement after surgery was not related to the degree of pain relief from the SI joint block.

Because all the people in this study had at least a 50% reduction in pain from the SI joint block, the researchers believe that this is an appropriate cutoff for predicting which people will benefit from surgery.

Using a more strict cutoff (≥75%) may mean that “a substantial number” of people who may benefit from SI joint fusion will never get it, said lead author of the study David W. Polly, Jr., MD, who is Professor and Chief of Spine Surgery in the Department of Orthopaedic Surgery at the University of Minnesota in Minneapolis.

iFuse System Is the Best Studied SI Fusion Technique

“This iFuse system is the best-studied SI fusion technique to date, and is the first minimally invasive fusion technique to be well studied,” Dr. Polly explained. “It does appear that in the long-term, patients treated with iFuse generally do better than patients treated with open surgery.”

What Is SI Joint Pain?

The SI joint connects your sacrum to your hip bones and is held together by a taut band of ligaments to keep it stable. If the joint is injured or the ligaments become stretched or torn, the joint can shift too much and cause pain and inflammation in the SI joint as well as the hips, low back, buttocks, and back of the legs. SI joint pain can make normal daily activities like sitting, walking up stairs, and even lying in bed difficult.

“The disability associated with this condition is greater than for hip or knee arthritis requiring joint replacement, spinal stenosis requiring surgery, and many other very disabling medical conditions,” Dr. Polly said.

“Pain in the buttock area is the classic presentation for SI joint pain,” Dr. Polly explained. However, diagnosis is complex as doctors must determine if the pain is coming from the SI joint, hip, or low back. “This is not necessarily easy to do. It requires a clinician who can do a physical exam as well as diagnostic spine and SI joint injections to differentiate these possible pain generators.”

sacroiliac joint anatomical illustration within the pelvis.The SI joint connects your sacrum to your hip bones and is held together by a taut band of ligaments to keep it stable. Photo Source:

Diagnosing and Treating SI Joint Pain

The physical exam involves a detailed exam of the spine, Dr. Polly said. Next, the hip joint is stressed (moved and stretched in different directions) to see if it is the source of the pain, Dr. Polly said.

“There are five key physical exam maneuvers that stress the SI joint (pelvic gapping, pelvic compression, thigh thrust, flexion abduction external rotation FABER test and Gaenslen’s test),” Dr. Polly said. “If three of these tests are positive, the probability is about 85% that patients with a well done injection test (SI joint block) will be positive, yielding pain relief temporarily. All the patients in the study had at least three positive physical exam tests.”

“Like everything in medicine, diagnosis of SI joint dysfunction often involves a combination of listening to the history, doing the physical exam and proper stress tests, and then doing the SI joint injection,” Dr. Garfin noted. “If the SI joint injection doesn’t result in 100% pain relief, that doesn't mean that the SI joint is not causing the pain if you meet the other criteria with it. I think that is what is important about this study,” Dr. Garfin said.

“If patients meet these criteria, we can reliably make them better but not perfect,” Dr. Polly said. “Complete pain relief is rare, but significantly lessening the pain is common.”

In many patients, SI joint pain can be relieved with physical therapy, nonsteroidal anti-inflammatory medications, lifestyle changes, and joint injections. However, for patients with chronic (ongoing) pain lasting more than 6 months who have not responded to other options, SI joint fusion may be helpful.

Disclosure: Steven R. Garfin, MD is a paid consultant of and has an ownership interest in SI-BONE Inc.

Updated on: 09/05/19
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Sacroiliac Joint Pain Center
Steven R. Garfin, MD
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