A Novel Piriformis Injection Technique Utilizing Combined Fluoroscopy and Ultrasound - A Pilot Study

Piriformis syndrome is a constellation of symptoms associated with low back, gluteal, and sciatic pain. One treatment for piriformis syndrome is the injection of local anesthetic, steroid, or botulinum toxin into the piriformis muscle. Various approaches for needle navigation into the piriformis muscle have been described using fluoroscopy or ultrasound. This study introduces a new method of image guidance combining fluoroscopy and ultrasound.

The primary aim of this study was examining whether the imaging modality used for needle guidance was associated with significant differences in pre- and post-piriformis injection pain scores. Secondary objectives were assessing differences in adverse events and procedure time.

This study is a retrospective cohort study.

This study was conducted at Oregon Health and Science University's Comprehensive Pain Center, Portland, OR, USA.

Institutional chart review was performed from 09/21/2014 to 01/21/2020 to identify patients that underwent piriformis steroid injections which generated a list of 95 patients and totaled 154 procedures. Inclusion criteria were met for 78 patients and 109 procedures. Pain scores were modeled longitudinally using robust variance estimates. The nonparametric Kruskal-Wallis test was used for procedure duration, while adverse events were too rare to evaluate statistically.

Piriformis steroid injections using the combined ultrasound and fluoroscopy technique had the lowest mean post-procedure pain score of 1.3 (SD 1.7) and the largest change in pain with a score difference of -3.9 (SD 2.1). Procedure durations were 8 (quartiles 5 to 10), 10 (quartiles 7 to 13), and 11 minutes (quartiles 9 to 13) for fluoroscopy alone, ultrasound alone, and combined techniques, respectively. All 3 modalities had duration ranges of minimum time of 3-5 minutes and a maximum time of 25-28 minutes. Adverse events across all imaging strategies were noted in 5 patients at the time of procedure and in 7 patients during follow-up appointments, the most common symptom being transient leg weakness or numbness.

The major limitation is the retrospective collection of data. Another limitation is that 6 different providers performed the injections, which may influence procedural consistency. Additionally, the inclusion of subjects with low pre-procedure pain scores could create a floor effect that minimized the occurrence of clinically significant shifts in pain scores. Adverse events were too few across all groups to assess.

Piriformis injections using combined fluoroscopic and ultrasound guidance provides comparable efficiency to standard techniques and may result in improved accuracy into the target and thus improved efficacy. Larger prospective trials are required to comprehensively examine the efficacy of this novel technique.