Ultrasound-guided Sacroiliac Joint Radiofrequency Ablation: A Pilot Study

Background:

This study will examine the effectiveness of sacroiliac joint (SIJ) diagnostic sensory blocks and radiofrequency ablation (RFA) under ultrasound guidance. The sacroiliac joint (SIJ) is estimated to be the source of pain in 10-27% of patients suffering from mechanical low back pain. When pain is refractory to conventional treatments (such as activity modification, exercise, physical therapy, chiropractic, anti-inflammatory and analgesic medications and corticosteroid injections), radiofrequency ablation (RFA) is a treatment option in carefully selected individuals.

Current practice is to perform the SIJ posterior sensory blocks and RFA under fluoroscopic guidance. Research has confirmed that SIJ RFA can provide significant relief, however, the success rate and magnitude of relief are variable. Part of this variability may relate to the challenging nature of identifying key anatomical landmarks under fluoroscopy - their location may not be clearly evident with fluoroscopy particularly if the patient is obese, has low bone mineral density or has abundant bowel gas and/or stool in the pelvis.

A recent cadaveric study by our research group has clarified the sensory innervation of the SIJ and the findings have implications for currently practiced SIJ sensory block and RFA procedures. The study confirmed that the posterior sacral network innervates the SIJ and runs along the lateral crest of the sacrum between the S1 and the S3 lateral sacral tubercles. Inasmuch as the lateral sacral crest is predictably and clearly visible on ultrasound, posterior sacral network (PSN) SIJ sensory blocks and RFA under ultrasound guidance may be feasible using the lateral sacral crest as the key anatomical structure.

No clinical studies have been done that use ultrasound guidance for SIJ RFA. There are numerous advantages to ultrasound-guided SIJ sensory block and RFA. Significantly, patients would no longer be exposed to ionizing radiation for their SIJ procedures. With an improved understanding of SIJ sensory innevation and technical improvements in RFA electrodes, we hypothesize that ultrasound guided SIJ diagnostic sensory blocks and RFA will lead to clinically significant outcomes that will be at least comparable to conventional fluoroscopic-guided techniques.

Objectives:

1. To evaluate the relative effectiveness of ultrasound-guided PSN sacroiliac joint sensory block compared to fluoroscopic-guided lateral branch sacroiliac joint block.
2. To evaluate the relative effectiveness of ultrasound-guided PSN sacroiliac joint radiofrequency ablation compared to fluoroscopic-guided lateral branch sacroiliac joint RFA.

Methodology:

This study is a prospective cohort study examining the effectiveness of ultrasound-guided SIJ sensory block and RFA of the PSN, compared to fluoroscopic guided SIJ RFA. Participants will first undergo a local anesthetic block under ultrasound guidance to determine the predictive value of this test for SIJ RFA; they will then undergo the SIJ RFA procedure. For some patients in this study, this will be a repeat RFA procedure as they would have had a previous fluoroscopic-guided SIJ RFA with success, but subsequent return of their pain.

SIJ Sensory Block: Eligible study subjects will initially undergo a lidocaine block of the PSN at the lateral crest under ultrasound guidance. Their index pain intensity prior to the block must be >2/10. Under ultrasound guidance, 0.5 mL of 2% lidocaine will be injected from the inferomedial border of the PSIS to the third transverse sacral tubercle at approximately 1.5 cm intervals along the skin surface. Following the local anesthetic block, the subject will be asked to complete a pain diary for 6 hours. Specifically, their baseline pain will be reassessed and their ability to perform functional activities will also be assessed over that time period. The results of this block will be compared to the results of conventional blocks done under fluoroscopy.

SIJ RFA: Ultrasound-guided RFA of the PSN will be performed using the same technique as the local anesthetic block with the exception that 2 Nimbus multitined electrodes will be used in a bipolar configuration. The electrodes will be placed along the lateral crest using a sequential, leap-frogging technique from the inferomedial aspect of the PSIS (at or just above the level of the S1 dorsal sacral foramen if visible, or the S1 spinous process if not) to the third transverse sacral tubercle at 1.5-2 cm intervals at the skin surface. A radiofrequency current will be passed for 120 seconds per site thus raising the temperature at the dorsal periosteum and adjacent soft tissue to 80°C resulting in thermal coagulation of the plexus. Prior to performing the thermal lesion, electrical stimulation at 2 Hz and 2.0 V will be administered. If the patient perceives, or the operator observes muscle contraction of the leg or anal sphincter, no radiofrequency current will be applied and the needle tip will be adjusted to a position away from where the sacral nerve roots may lie.

Analysis:

The effectiveness of ultrasound-guided sensory blocks and RFA will be directly compared to the effectiveness of fluoroscopic-guided sensory blocks and RFA. In patients who have had the SIJ RFA procedure previously, their current ultrasound-guided PDQQ-S scores will be compared to their previous fluoroscopic-guided PDQQ-S results. In patients who are receiving the SIJ RFA procedure for the first time, a database of SIJ RFA PDQQ-S scores of patients treated over the past 5 years with the fluoroscopic-guided RFA technique is available for comparison. Their results will be compared to age and pre-RFA matched patients from the database.