The Diagnostic Funnel: A Multi-Stage Diagnostic Selection Protocol for Minimally Invasive Sacroiliac Joint Fusion.

Background Minimally invasive sacroiliac joint fusion (MI SIJF) is an established intervention for chronic sacroiliac joint dysfunction, yet outcome variability across the literature suggests that surgical success may heavily depend on preoperative selection accuracy. Traditional diagnostic pathways relying on transient anesthetic blocks are susceptible to false-positives and variable responder rates. The purpose of this study is to evaluate the clinical effectiveness of a rigorous, multi-stage selection protocol, termed the "diagnostic funnel," which utilizes a therapeutic durability threshold to ensure diagnostic specificity and optimize outcomes following MI SIJF. Methodology A retrospective chart review of 17 patients who underwent 19 MI SIJF procedures between January 2024 and August 2025 was conducted. To qualify for surgery, patients were required to meet all three stages of the "diagnostic funnel": 1) chronic non-radicular pain (>6 months) with a positive Fortin finger sign, 2) at least three out of six positive provocative physical maneuvers (SI [sacroiliac] compression, ASIS [anterior superior iliac spine] distraction, Gaenslen's test, FABER [flexion, abduction, external rotation)], thigh thrust, and Yeoman's test), and 3) a "durability threshold" defined as at least 70% pain relief maintained for a minimum of 14 days following an image-guided intra-articular corticosteroid injection. Surgical success was measured at the six-month follow-up by mean percent reduction in visual analog scale (VAS) pain scores and the proportion of patients achieving the minimal clinically important difference (MCID, defined as a ≥20-point VAS reduction). Results The cohort demonstrated 100% adherence to the multi-stage selection protocol. The most frequently positive provocative maneuvers were Gaenslen's test (94.7%), thigh thrust (89.5%), and FABER (89.5%). At six months postoperatively, patients achieved a mean VAS pain score reduction of 74.7%. Additionally, 94.4% of procedures successfully met or exceeded the MCID threshold for clinical success. Conclusion In this retrospective series, preoperative patient selection utilizing the multi-stage "diagnostic funnel" was associated with high clinical success rates. Replacing transient local anesthetic blocks with a 14-day corticosteroid "durability threshold" provides a more stable prognostic indicator of true intra-articular pathology. Adopting this diagnostic framework may allow spine surgeons to increase diagnostic specificity and consistently optimize postoperative pain reduction in MI SIJF patients.