Sacroiliac joint injections, lateral branch ablation and fusion

Sacroiliac pain has intra-articular and dorsal extra-articular components. Diagnose with a battery of provocation tests plus low-volume blocks, ablate the S1–S3 lateral branches for extra-articular pain, and reserve fusion for carefully selected patients.

1. Use a battery of provocation tests. Three or more of six tests, or any two of four selected tests, best predicted response to intra-articular anesthetic blocks; when all six are negative, the joint can be ruled out ¹.
2. Keep intra-articular volume small. The 2025 consensus recommends a maximum of about 2.5 mL for intra-articular injections, stopping sooner if resistance is met, to avoid capsular rupture and extra-articular spread that reduce specificity ².
3. Lateral branch ablation targets S1–S3. The dorsal sacroiliac complex is supplied by the L5 dorsal ramus and S1–S4 lateral branches; S1–S3 should always be targeted (grade A), with L5 and S4 considered (grade B) ².
4. Use at least 50% relief before ablation. Prognostic sacral lateral branch blocks are positive at 50% relief, because ablation relief is generally less than block relief ².
5. Fusion selection is stricter. The consensus recommends dual steroid-free intra-articular blocks with a high relief threshold and documented functional improvement before fusion (grade I) ².
6. Fusion evidence is mixed. Two pragmatic trials favored fusion, but a double-blind sham-controlled trial found no significant difference from sham at 6 months (−1.0 points, 95% CI −2.2 to 0.3) ²³.

Imaging degeneration and tenderness do not establish the sacroiliac joint as the pain source; confirm with provocation tests and blocks before any invasive treatment ²¹.

• Laslett: three of six positive provocation tests best predicted a positive block ¹.
• In cadavers, S1–S3 contribute dorsal innervation in more than 90% of specimens ².
• Volumes above 3 mL are sometimes needed for combined intra- and extra-articular pathology ².
• A single provocation test is not sufficient to make the diagnosis ¹.
• The sham fusion trial enrolled 63 patients, 94% of them women ³.
• Prior lumbar fusion increases sacroiliac motion and the prevalence of sacroiliac pain, especially after L5–S1 fusion ².
• The consensus found the battery of examination tests sensitive but less specific for intra-articular pathology, with negative tests most informative ².
• In the sham trial, mean pain fell 2.6 points after fusion and 1.7 points after sham surgery ³.

• Selecting a fusion candidate on one block or one provocation test ²¹.
• Injecting large volumes intra-articularly and calling the result diagnostic ².
• Ablating only S1 and S2 and expecting complete dorsal denervation ².
• Counting the sham-controlled fusion trial as positive because pain improved in the fusion arm ³.