Performing a Piriformis Muscle Injection
The piriformis muscle serves as an external rotator of the hip joint (3). The muscle arises from the sacrum and inserts onto the greater trochanter (5). Entrapment of the sciatic nerve within the piriformis muscle can cause pain and numbness in the buttocks that can also radiate down the leg (2). The sciatic nerve will typically exit the pelvic cavity deep to the piriformis muscle (3). However, other variations exist including the nerve passing through the piriformis and also passing superior to the piriformis muscle (3). It is estimated that 6 to 8% cases of low back pain diagnoses are secondary to piriformis syndrome (1). Historically, diagnosis of piriformis syndrome is made when patients meet two of the three following criteria. First, they must have pain at the intersection of the sciatic nerve and the piriformis muscle on the FAIR test (1). The FAIR position is seen below, which involves flexing, adducting, and internally rotating the hip. Then, downward pressure is applied to the flexed knee and pain should be provoked within the piriformis muscle (1).
The second criteria is tenderness at the intersection of the piriformis and the sciatic nerve. Finally, the third criteria is a positive supine straight leg test (Lasegue’s sign) (1).
Ultrasound guided injections of the piriformis muscle have been found to be more accurate than fluoroscopic guided injections (4). Injection of the piriformis muscle or piriformis tendon sheath is one potentially diagnostic and treatment option for piriformis syndrome. The transducer used is typically a curvilinear probe (5-1 or 5-2 MHz). The patient is first placed in the prone position and a pillow can be placed between the bed and the patient’s inguinal area to increase pelvic tilt and improve visualization of the piriformis muscle (5).
The piriformis muscle can be identified deep to the gluteus maximus muscle (3). The transducer is usually placed first over the posterior superior iliac spine (3). Then, the probe is moved inferiorly until the sacrum is lateral and the posterior inferior iliac spine is medial. As the probe travels distally, the ilium disappears because this is the start of the greater sciatic notch (3). At this location, the piriformis can be seen travelling in a cephalomedial to cephalolateral direction (3). In order to confirm that the piriformis muscle is being visualized, the hip should be internally and externally rotated and motion of the piriformis muscle is visualized (3). Below are three different views of the piriformis muscle all with the ilium inferior.
Prior to any injection, the sciatic nerve should be identified to prevent incidental injury to the nerve (2). The sciatic nerve can be found at the lateral edge of the ischial tuberosity and between the gluteus maximus and quadratus femoris muscle (2).
At the previously discussed location visualizing the piriformis muscle, a 22 gauge 3.5 inch needle is guided in a lateral to medial direction into the piriformis muscle or tendon sheath (3). However, the muscle or tendon sheath can also be injected from a medial to lateral direction (4).
The piriformis muscle injection can be useful min aiding in diagnosis and potentially with treatment of piriformis syndrome. An ultrasound guided injection has been found to be an accurate and safe way to perform the injection.
By Gregory Rubin, DO
1) Fishman, Loren M., et al. “Piriformis Syndrome: Diagnosis, Treatment, and Outcome–a 10-Year Study.” Archives of Physical Medicine and Rehabilitation, vol. 83, no. 3, Mar. 2002, pp. 295–301. PubMed, https://doi.org/10.1053/apmr.2002.30622.
2) Chang, Ke-Vin, et al. “Ultrasound Imaging and Guided Injection for the Lateral and Posterior Hip.” American Journal of Physical Medicine & Rehabilitation, vol. 97, no. 4, Apr. 2018, pp. 285–91. PubMed, https://doi.org/10.1097/PHM.0000000000000895.
3) Payne, Jeffrey M. “Ultrasound-Guided Hip Procedures.” Physical Medicine and Rehabilitation Clinics of North America, vol. 27, no. 3, Aug. 2016, pp. 607–29. PubMed, https://doi.org/10.1016/j.pmr.2016.04.004.
4) Finnoff JT, Hurdle MF, Smith J. Accuracy of ultrasound-guided versus fluoroscopically guided contrast-controlled piriformis injections: a cadaveric study. J Ultrasound Med 2008;27:1157–63.
5) Chen, Carl P. C., et al. “Ultrasound-Guided Injection of the Piriformis Muscle.” American Journal of Physical Medicine & Rehabilitation, vol. 90, no. 10, Oct. 2011, pp. 871–72. PubMed, https://doi.org/10.1097/PHM.0b013e31822de72c
6) Bardowski, Elizabeth A., and J. W. Thomas Byrd. “Piriformis Injection: An Ultrasound-Guided Technique.” Arthroscopy Techniques, vol. 8, no. 12, Dec. 2019, pp. e1457–61. PubMed, https://doi.org/10.1016/j.eats.2019.07.033.
7) Smith, Jay, et al. “Ultrasound-Guided Piriformis Injection: Technique Description and Verification.” Archives of Physical Medicine and Rehabilitation, vol. 87, no. 12, Dec. 2006, pp. 1664–67. PubMed, https://doi.org/10.1016/j.apmr.2006.08.337.