SI Joint Fusion Shows High Success Rate Regardless of Level of Response to SI Joint Block

David W. Polly, Jr., MD, and Steven R. Garfin, MD, Comment

Peer Reviewed

Patients who underwent sacroiliac joint (SI) joint fusion using the iFuse Implant System showed a high success rate regardless of their level of response to diagnostic SI joint block, according to a study in the International Journal of Spine Surgery.

Lead author David W. Polly, Jr., MD, has been involved in numerous clinical trials with “robust high-quality data demonstrating good results” with the triangular titanium porous coated implants, known as the iFuse Implant System. However, the results did not seem to correlate with injection response, he explained.

“North American Spine Society (NASS) established a policy requiring ≥75% pain relief [on 2 consecutive SI joint injections] to meet the surgery criteria for SI joint surgery. I did not think this was correct,” explained Dr. Polly, who is Professor and Chief of Spine Surgery in the Department of Orthopaedic Surgery at the University of Minnesota in Minneapolis.

data analysisLead author David W. Polly, Jr., MD, has been involved in numerous clinical trials with “robust high-quality data demonstrating good results” with the triangular titanium porous coated implants, known as the iFuse Implant System. Photo

Data Derived From Two Prospective Trials

To better understand the relationship between response to SI joint block and fusion outcomes, Dr. Polly and colleagues examined data from two prospective multicenter trials of SI joint fusion in 320 subjects with SI joint dysfunction diagnosed by history, physical exam, and standardized diagnostic SI joint block (ie, ≥50% reduction in pain at 30 or 60 minutes following SI joint block). The studies were sponsored by SI-BONE.

At 6-months postsurgery, the patients showed a mean reduction in Visual Analog Scale (VAS) SI joint pain of 50.9 points (scale 0-100) and a mean reduction on Oswestry Disability Index (ODI) of 24.6 points (P<0.0001 compared to baseline). Similar results were found at 12-month followup, with reductions of 50.8 points and 25.8 points, respectively.

In multiple analyses, absolute reduction in VAS scores at 6- and 12-months postsurgery were not significantly correlated with the average reduction in pain found with SI joint block. In addition, the proportion of subjects achieving a predetermined threshold of 20-point improvement in VAS score or 15-point improvement in ODI score at 6-month followup was high across the spectrum of SI joint block responses (range, 77.1%-84.8% for VAS score and 59.4%-75.0% for ODI score).

Clinical Implications

Thus, the study demonstrates the ≥75% pain relief cutoff is not required to predict a good result from surgery, Dr. Polly told SpineUniverse. Instead, a cutoff of “≥50% pain relief as per the clinical trial inclusion criteria is an adequate response to merit surgical consideration,” he said.

The findings by Polly et al 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.

Despite these findings, insurance companies often follow the criteria set up by NASS and other organizations, Dr. Garfin noted. “The insurance carrier may say ‘Sorry, you don’t meet NASS criteria because you are only saying 50% relief,’” he noted.

Hopefully, Dr. Garfin said, findings such as these by Polly et al that provide a surgical correlate following SI joint block results may allow for a reassessment of the NASS criteria in the future. In addition, he emphasized that accessing the SI joint via injection is challenging and that, in less experienced hands, there may be a high rate of false negative results with SI joint injection. 

“That is why you have to put everything else into perspective,” Dr. Garfin said, referring to the appropriate history and the need to demonstrate positive findings on at least 3 of the 5 key physical exam tests for SI joint dysfunction.

The findings emphasize the need to clearly define the target population for SI joint fusion given that several high-quality  studies—two randomized controlled trials (INSITE and Imia), 1 prospective cohort study (SIFI), three level 3 studies, and a myriad of level 4 studies—demonstrate consistent benefit from this intervention, Dr. Polly explained. Overly strict selection criteria may preclude “a substantial number” of patients who may benefit from SI joint fusion from having the surgery, the researchers noted in the study.

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

iFuse System is Best Studied Fusion Technique for the SI Joint

The fusions in this study were performed using the iFuse Implant System, which is a minimally invasive device made of titanium implants (triangular-shaped rods) that attached horizontally across the sacrum and ilium.

“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. “The collateral damage is far less with this minimally invasive technique compared to the prior open techniques. It does appear that in the long-term, patients treated with iFuse generally do better than patients treated with open surgery.”

A Look Ahead to Future Research

Dr. Polly suggested that future research should delineate “how low of a response to injection is enough of a response to consider surgical intervention. Traditionally, we use ≥50% as a cutoff. This may or may not be accurate.”

“The clinical trials used in this study required 3 of 5 positive provocative physical exam findings, which has an 85% positive predictive value for a positive response to local anesthetic injection,” Dr. Polly added.

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

Updated on: 05/11/19
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Transsacral Fixation Is Linked to High Fusion Rate and Improved Quality of Life in Adult Scoliosis
David W. Polly, Jr., MD
Professor and Chief of Spine Surgery
University of Minnesota
Department of Orthopaedic Surgery
Minneapolis, MN
Steven R. Garfin, MD
Distinguished Professor and Chair
Department of Orthopaedics
University of California, San Diego
San Diego, CA

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