Ultrasound-guided injection of the intrapelvic portion of the obturator internus in a cadaver model

BACKGROUND AND OBJECTIVES: Musculoskeletal dysfunction of the pelvic floor is common. One of the intrapelvic muscles, the obturator internus (OI), can be substantially stressed during its sharply angulated exit from the pelvis. However, there may be considerable overlap between symptoms and signs arising from the OI and other potential pain generators including the levator ani in the pelvic region. Accurate diagnosis for the OI might permit more efficient treatment combined with OI-specific exercise and behavior modification. Therefore, we hypothesized that ultrasound (US)-guided needle insertion in the intrapelvic portion of the OI would be accurate when a pararectal approach is used for diagnostic and therapeutic purposes. METHODS: Bilateral US-guided intramuscular injections in the pelvic area were performed using 6 fresh, nonembalmed male cadavers. When the needle was positioned in the targeted muscle, 0.5 mL of green filler was injected. After the injection procedure, each specimen was dissected to evaluate the accuracy of US-guided injection into the intrapelvic portion of the OI. RESULTS: Twelve injections were made into the targeted muscles in the 6 cadaveric specimens. All injections placed filler into the OI muscles just medial to the inferior pubic ramus. There was no case in which a needle passed through unintended structures, such as neurovascular structures. CONCLUSIONS: The newly developed US-guided pararectal approach allowed accurate insertion of a needle into the intrapelvic portion of the OI. This US-guided method facilitated a more precise approach to the intrapelvic portion of the OI and may help differentiate conditions or symptoms caused by other structures.