Background: Approximately 6% to 8% of lumbar pain cases, whether associated with
radicular pain or not, may be attributed to the presence of piriformis muscle syndrome.
Available treatments, among others, include pharmacotherapy, physical therapy, and injections
of different substances into the muscle. Various methods have been used to confirm correct
needle placement during these procedures, including electromyography (EMG), fluoroscopy,
computed tomography (CT), or magnetic resonance imaging (MRI). Ultrasonography (US) has
now become a widely used technique and therefore may be an attractive alternative for
needle guidance when injecting this muscle.
Objective: The objective of this study was to assess the reliability of US in piriformis injection
of patients with piriformis syndrome.
Study Design: Feasibility study; 10 patients with piriformis muscle syndrome were injected
with botulinum toxin A using a US-guided procedure. Then patients were administered 2 mL
iodinated contrast and were then transferred to the CT scanner, where they underwent pelvic
and hip imaging to assess intramuscular distribution of the iodinated contrast.
Setting: Multidisciplinary Pain Management Department in Spain.
Results: Of all 10 study patients (8 women, 2 men), 9 had intramuscular or intrafascial
contrast distribution. Distribution did not go deeper than the piriformis muscle in any of the
patients. The absence of contrast (intravascular injection) was not observed in any case.
Limitations: The main limitation of our study is the use of ionizing radiation as confirmation
technique.
Conclusion: Ultrasound-guided puncture may be a reliable and simple procedure for
injection of the piriformis muscle, as long as good education and training are provided to the
operator. US has a number of advantages over traditional approaches, including accessibility
and especially no ionizing radiation exposure for both health care providers and patients.
Key words: Piriformis, ultrasound-guidance, CT, pain, chronic pain, ultrasonography,
botulinum toxin, sciatica
Computer-Tomographic Verification of
Ultrasound-Guided Piriformis Muscle Injection:
A Feasibility Study