typically affected the SI joints and the pubic symphysis. These joints often had demonstrable instability and were difficult to treat with the smaller 7.0 mm screws even when cement was added. Additionally, the failure rate was unacceptably high. In 2009, SI-BONE launched triangular titanium bars that were designed for SI joint fusion, and by 2015 there was a Category I CPT code for SI joint fusion and a Level I randomized control trial supporting the efficacy of this technique.
The first dorsally placed allograft appeared in 20122
and quickly gained
popularity in treating distraction-type arthrodesis due to the ease of the approach and the optimal safety of the procedure. I adopted this technique for certain patients who couldn’t undergo general anesthesia or who had a contraindication to the lateral approach for SI joint arthrodesis. Interventionalists began to adopt this approach for SI fusion and the increased popularity caught the attention of the surgeon community who maintained that this was a different procedure and should have a different CPT code associated with it.
In 2023, dorsal SI joint fusion with an intra-articular allograft was assigned a Category III code, which was converted back to a new Category I code in 2024 based on a new CPT application submitted with supportive data. The new code for the dorsal approach is 27278 as compared to the original lateral or posterolateral approach code of 27279 or the open SI joint fusion code, which is 27280. Despite the slightly more invasive nature of the latter two codes, all of the techniques of SI joint fusion have become far less invasive over the past 2 decades.
JH: Can you walk me through how to evaluate a patient and determine if they are an ideal candidate for this procedure? DB: Selecting patients for SI joint fusion is very different from selecting patients for lumbar fusion. The SI joint only moves a small amount (1.4–3.1 mm in any direction)3
and degenerative changes
are common at an early age even in patients with no SI joint pain.4
Unlike many other joints that may undergo Douglas Beall, MD, FSIR
SI joint fusion was also used in patients with chronic pelvic instability, which typically affected the SI joints and the pubic symphysis. These joints often had demonstrable instability and were difficult to treat with the smaller 7.0 mm screws even when cement was added.
fusion, imaging mainly plays a role in SI joint fusion to detect pathologic entities that are not amenable to fusion, such as inflammatory changes or erosions from spondyloarthropathies, sacral fracture, or a tumor such as a chordoma. No imaging modality has been shown to have good diagnostic value for detecting a painful SI joint. In lieu of that, a combination of physical examination tests for SI joint pain and the patient response to an SI joint injection test is used to determine the optimal candidates for SI joint fusion.
Even before these tests are used to select the patients, the clinical history is very important for determining the patients with SI joint pain as opposed to
those with lower lumbar and hip pain— both of which can present with similar signs and symptoms. Patients who have prior trauma or a previous long- or short-segment fusion that traverses L5-S1 are typical for those who develop SI joint pain. So are women with long- standing, postpartum pelvic instability.
Once at-risk patients are identified, SI joint injections may be performed. We look for an injection test result of 75% or more pain relief, which indicates a positive test and an appropriate candidate for SI joint fixation. The physical examination tests for SI joint pain, which are critical for evaluating for SI joint pain, include:
• Pelvic compression test • Pelvic distraction test • Sacral thrust test • Gaenslen’s (pelvic torsion) test • Faber’s test • Thigh thrust test
SI joint dysfunction is diagnosed when three of six physical examination tests are positive. When three out of five physical examination tests are positive there is an 85% pretest probability that an SI joint injection will be successful,5 and there is a 91% sensitivity and 78% specificity for SI joint–related pain.6
JH: How has this been received by competing specialties in your area? DB: The introduction of less invasive techniques for SI joint fusion has not only resulted in shorter surgery times, less blood loss and fewer days in the hospital, but it also results in better clinical outcomes versus open SI joint fusion.7,8
The minimally invasive
technique has also attracted more interventional pain management and interventional radiology physicians who now routinely perform SI joint fusions. In fact, data from the Center for Medicare and Medicaid Services have shown that the majority of minimally invasive SI joint fusions are performed by individuals in the “nonsurgical specialties.”9
There
has also been rapid growth in the minimally invasive procedures that are offered in ambulatory surgical and outpatient centers.9
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