Joint Radiofrequency Ablation

Fig. 16.1

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).

../images/457420_1_En_16_Chapter/457420_1_En_16_Fig2_HTML.jpg — Fig. 16.2

Model illustrating the course of the posterior innervation (lateral branches of S1 – yellow, lateral branches of S2 – green, lateral branches of S3 – blue, branches from L5 dorsal ramus and lateral branches of S4 – dotted red, posterior sacral network – purple) to the sacroiliac joint relative to the transverse sacral tubercles (circled numbers). In one anatomic study, 80% of cadaveric specimens had a posterior sacral network that was bordered by the second and third transverse sacral tubercles. Twenty percent of specimens had a proximal border that extended superior to the second transverse sacral tubercle but below the first transverse sacral tubercle. A short, separate S1 lateral branch that innervated the sacroiliac joint was present below the first transverse sacral tubercle in 32% of specimens, and superior to the first transverse sacral tubercle in 8% of specimens. (Reprinted with permission from Wolters Kluwer Health, Inc.)

Patient Selection

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.

Ultrasound Scanning

Probe: C5-2 MHz curved transducer.
Position: prone

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).