Distribution pattern of sonographically guided iliopsoas: Injections cadaveric investigation using coned beam computed tomography

Objectives: To investigate the distribution pattern of sonographically guided iliopsoas (IP) injections in an unembalmed cadaveric model. Methods: A single experienced operator completed 10 sonographically guided IP injections in 5 unembalmed cadaveric pelvic specimens (4 male and 1 female; ages 55-95 years; body mass indices, 15.5-27.5 kg/m²) using a previously described in-plane, lateral-to-medial approach short axis to the tendon. Each injection consisted of 7 mL of a 20% dilution of contrast material injected between the IP tendon and the acetabular rim using a 22-gauge, 87.5-mm (3 1/2-in) needle. To facilitate interpretation of contrast patterns, 2 additional injections were performed on single hips: sonographically guided 14 mL contrast-latex IP injection and sonographically guided superficial IP "peritendinous" injection with 7 mL of contrast-latex. Immediately before and after each injection, fluoroscopic images were obtained with a fixed C-arm equipped with coned beam computed tomography. After each injection, radiographic images were evaluated by a board-certified, fellowship-trained musculoskeletal radiologist to determine injectate distribution. Specimens receiving contrast-latex injections were dissected 48 hours after injection to determine the anatomic location of the injectate. Results: Nine of 10 IP injections (90%) produced characteristic "U-shaped" flow patterns covering 50% to nearly 100% of the IP tendon circumference and resembling previously published IP bursograms. One injection was excluded because the majority of the latex was within the pectineus muscle, likely due to technical factors. Latex flowed an average of 5.3 cm (range, 0.3-7.9 cm) cephalad and 5.2 cm (range, 1.0-7.5 cm) caudad to the acetabular rim. The large-volume (14-mL) IP injection produced a similar flow pattern to the 7 mL injections, whereas the superficial peritendinous injection produced a contrast pattern consistent with intramuscular flow. Subsequent dissection confirmed bursal flow for the 14-mL injection, whereas the superficial peritendinous injection placed latex within the superficial portion of the IP muscle (ie, intramuscular). Conclusions: Sonographically guided IP injections using an in-plane, lateral-to-medial technique place injectate into the IP bursa between the IP tendon and the acetabular rim. Within the limits of this cadaveric investigation, this sonographically guided 7-mL IP "bursa" injection may provide a minimum of 50% circumferential IP tendon coverage and approximately 5 cm of cephalad and caudad flow. There does not appear to be a peritendinous space deep to the IP tendon at the acetabular rim that is both outside the bursa and amenable to sonographically guided injection. Injections into the superficial aspect of the IP using 7-mL volumes may not deliver injectate deep to the IP tendon and therefore may represent a fundamentally different injection.