Clinical Outcomes Following Minimally Invasive Sacroiliac Joint Fusion With Decortication: The EVoluSIon Clinical Study

Study Design

This interim report includes all patients participating in a prospective, multicenter evaluation of the commercially available SImmetry Sacroiliac Joint Fusion System (Surgalign Spine Technologies, Deerfield, IL) in the EVoluSIon (EVSI) study, registered on clinicaltrials.gov as NCT02074761. The EVSI study enrolled 250 patients at 23 centers in the United States. The study is now closed to enrollment and is in follow-up. The protocol was approved either by a central institutional review board (IRB) or by each participating center’s IRB, and written informed consent was obtained from all patients prior to enrollment. Patients were screened from each investigator’s population of patients indicated for MI SIJF. Patients receiving or seeking workers’ compensation benefits were excluded. The key inclusion criteria for participation were 18 years or greater; at least 6 months of nonoperative management of SI joint pain; 3 positive provocative tests (such as FABER, gaenslen, compression, thigh thrust, and distraction);9 at least 1 positive diagnostic SI joint injection that resulted in at least a 50% reduction in pain within 6 months prior to implantation;10,11 visual analog scale (VAS) SI joint pain score of 60 or greater; and Oswestry Disability Index (ODI) score of at least 40. Patients (n = 23) who did not meet minimum eligibility requirements for baseline VAS or ODI scores were not excluded from the analysis to limit influence of bias from analysis. These and any other protocol noncompliance events were reported to the investigating sites’ IRB, as required.

Surgical Procedure

The MI SIJF surgical procedure included use of the SImmetry System in accordance with the approved labeling. The implant system includes a 12.5-mm diameter cannulated implant placed through the location of decortication and an 8.5-mm diameter antirotational implant for mechanical stability. Both devices are threaded implants made of Ti-6Al-4V titanium alloy with a microscale texture designed for osseointegration.

The procedure has been described in detail elsewhere.3,12,13 Briefly, 4 steps are followed: MI lateral access, joint preparation via decortication, bone graft placement, and implant delivery (Figure 1). Joint preparation is a key step in the MI SIJF procedure with the SImmetry System using a proprietary decorticator to remove cartilage and prepare up to 50% of the SI joint surface as an active bleeding fusion bed for bone graft material. Bone graft is then packed into the decorticated area, before the cannulated implant is placed across the area of decortication. A secondary antirotational implant is then placed for biomechanical stability.14

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Figure 1

(A) Minimally invasive lateral access of the sacroiliac joint; (B) decortication of the joint (inset: user-interface of decorticator instrument); (C) delivery of bone graft into the actively bleeding fusion bed (inset: fluoroscopic image during decortication); and (D) final placement of the threaded implant through the area of decortication and a secondary device for stability.

Outcomes

Baseline data collection included medical history, prior treatments and surgeries, provocative maneuvers to confirm the diagnosis of SI joint dysfunction, diagnostic SI joint injections within 6 months prior to implantation (sites followed their standard of care for diagnostic injections; however, at least 1 diagnostic injection was required to be within 6 months of the SImmetry procedure; this was needed to diagnose and treat SI joint dysfunction), and pain medication usage. Patients were asked to complete a questionnaire, which included self-evaluation of various elements: (1) SI joint pain as measured by a VAS from 0 to 100, where 0 represented no pain and 100 represented the worst possible pain; (2) disability due to low back pain as measured by the validated ODI survey; and (3) quality of life through the EQ-5D questionnaire. The patient questionnaires and pain medication usage were collected preoperatively and at specified timepoints of 6 weeks, 3 months, 6 months, and 12 months postoperatively. Patient questionnaires were self-reported and completed by each patient prior to meeting with the investigator to limit bias. Patient qualification and endpoint data were monitored, and the source was verified for accuracy in reporting and compliance. Data were collected and reported via electronic database (Fortress Medical Systems, Hopkins, MN).

VAS pain and ODI reductions were also defined in terms of minimal clinically important difference (MCID) of 20 points on the VAS scale and 15 points on the ODI scale.3 Multiple secondary analyses were defined in the protocol, including comparison of baseline and procedural data to outcomes of pain reduction and fusion. EQ-5D is a widely used standardized measure of health status consisting of a patient-completed questionnaire with 5 quality-of-life questions that can be combined into a single index of “preference weights,” representing the time trade-off of current health. A VAS-like pain scale is also included, where 0 is the worst imaginable health state and 100 is the best imaginable health state.15,16

SIJF was assessed by an independent core laboratory at the 12-month follow-up visit via thin-slice (<2 mm) computed tomography (CT), viewing 4 consecutive cuts on both coronal and sagittal reconstructions. Radiographic evidence of fusion was defined as presence of a continuous segment of bridging bone that extends from the sacrum to the ilium. This qualitative assessment of fusion status was performed by trained, independent radiologists, including 2 evaluators and an adjudicator (in case of a disagreement). Fusion status was classified according to the following preestablished criteria shown in Table 1. Examples of each fusion category using representative CT scans from patients evaluated in this study are shown in Figure 2.

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Figure 2.

Examples of bridging bone categories.

In cases where an assessment could not be made from the available images due to technical factors (eg, obscured anatomy, poor contrast, or high parallax), the assessment was graded as “Indeterminate.” If an assessment could not be made due to missing films, the assessment was graded as “Unable to Assess.”

Statistical Analyses

Predefined statistical analyses described in the protocol include the primary endpoint analysis of VAS SI joint pain scores beginning with the 6-month follow-up visit. Pain relief postimplantation was evaluated at each follow-up interval with descriptive statistical analyses (mean, standard deviation, median, minimum and maximum).

Statistical analyses were performed using paired t tests to assess improvements following treatment using the preoperative and follow-up VAS, ODI, and quality-of-life measures for each patient over time. Confidence intervals of 95% on the mean changes from the preoperative result in ODI and VAS scores were computed. Procedural data were summarized with descriptive statistics and 95% confidence intervals. Subgroup analyses for the primary endpoints were planned to determine whether baseline or procedural characteristics differentiate subjects in terms of outcomes. Logistic and linear regression models were used for these analyses for binary vs continuous endpoints.

The McNemar test was used to determine the significance of the decreased usage of medications at the 1-year follow-up visit. This test compares the rate of patients who stop using opioids as a result of the SIJF procedure to the rate of patients who start taking opioids following the procedure; the relative rates are used to determine significance between groups.17 All statistical analyses were performed using the SAS statistical software package version 9.4 (Cary, NC).