Diagnostic Advantages of Proximal Sacroiliac Joint Injections for Relief of Mechanical Back Pain: A Retrospective Observational Cohort Study.

Background The sacroiliac joint (SIJ) is a common source of mechanical low back pain (LBP). Standard fluoroscopy-guided intra-articular injections typically target the distal (lower one-third) SIJ, but some patients fail to achieve relief, raising the possibility that the distal approach may not adequately access clinically relevant pain generators in the proximal fibrous SIJ. Objectives The primary objective was to evaluate the immediate diagnostic efficacy of the proximal (upper one-third) SIJ injection approach -- defined as ≥50% visual analog scale (VAS) reduction within 30 minutes of injection (reflecting the local anesthetic's diagnostic response rather than therapeutic benefit) -- in patients with mechanical LBP unresponsive to prior distal SIJ injections. Secondary objectives included evaluating complete pain resolution, demographic associations (age and sex), and procedural safety. Study design This was a retrospective observational cohort study. Setting The study was conducted at Och Spine-Center for Comprehensive Spine Care, Department of Physical Medicine and Rehabilitation, Weill Cornell Medicine, New York-Presbyterian Hospital. Methods Twenty-two adult patients with mechanical LBP who previously failed to achieve therapeutic relief from technically adequate distal SIJ injections performed by outside providers underwent fluoroscopically guided proximal SIJ injections by a single interventional physiatrist. Procedures targeted the upper third of the SIJ using a therapeutic injection of corticosteroid and local anesthetic. Baseline and post-injection pain scores were recorded using the VAS within 30 minutes pre- and post-injection to measure the immediate diagnostic response of the anesthetic. The primary outcome was the proportion of patients achieving ≥50% pain reduction in this immediate response. Secondary outcomes included complete pain resolution, associations with age or sex, and complications. Results All patients underwent technically successful proximal SIJ injections as confirmed by intra-procedural contrast dye patterns. The baseline VAS score (mean ± SD) was 4.86 ± 2.75, and the post-injection score was 1.14 ± 1.42, yielding a mean pain improvement of 79.6% ± 25.8% (p < 0.001). Twenty patients (90.9%) achieved ≥50% reduction in pain (95% confidence interval: 70.8%-98.9%), and 10 patients (45.5%) experienced complete resolution. No complications were reported. There were no statistically significant differences in outcomes by age or sex. Limitations This study was retrospective, with short-term follow-up limited to immediate post-injection pain scores. Functional outcomes and longer-term pain relief were not assessed. Patients were referred from multiple providers, potentially introducing selection bias. All proximal injections were performed by a single provider, potentially introducing performance bias. Future prospective studies should evaluate long-term outcomes, patient-reported functional measures, and relevant spino-pelvic parameters. Conclusions Proximal SIJ injections yielded high rates of immediate pain relief in patients who initially failed technically adequate distal injections. These findings suggest anatomical and diagnostic advantages of the proximal approach that may identify SIJ pain generators not accessed by distal injections. Prospective controlled studies are needed to evaluate whether the proximal approach warrants earlier consideration in the mechanical SIJ pain treatment algorithm.