Posterior innervation of the sacroiliac joint from the posterior sacral network. S1, S2, and S3 indicate the S1, S2, and S3 posterior sacral foramen. The lateral branches from these levels (S1, yellow; S2, green; and S3, blue) contribute to the posterior sacral network (purple). Occasionally, a branch from the L5 dorsal ramus (red) and/or the S4 lateral branches (not pictured) also contribute to the network. (Reprinted with permission from Wolters Kluwer Health, Inc.)
The PSN courses over the periosteum and traverses the lateral sacral crest, primarily between the second and third transverse sacral tubercles. In some cases, an S1 lateral branch contributes directly to the innervation of the joint (Fig. 16.2).
Sacral lateral branch blocks are preferred over intraarticular sacroiliac joint injections when selecting patients for radiofrequency ablation, as the latter targets structures not innervated by the PSN. Eligible patients should demonstrate at least 50% pain relief after the block.
Probe: C5-2 MHz curved transducer.
A transverse scan of the sacrum is performed in a caudad to cephalad direction to identify transverse sacral tubercles (TST) 1–4 which serve as landmarks during radiofrequency lesioning procedures of the PSN (Fig. 16.3).