Sonographically guided obturator internus injections: techniques and validation.

Objectives: The primary purpose of this investigation was to describe and validate sonographically guided techniques for injecting the obturator internus (OI) muscle or bursa using a cadaveric model.

Methods: A single experienced operator completed 10 sonographically guided OI injections in 5 unembalmed cadaveric pelvis specimens (4 female and 1 male, ages 71-89 years with body mass indices of 15.5-24.2 kg/m2). Four different techniques were used: (1) OI tendon sheath (4 injections), (2) OI intramuscular (2 injections), (3) OI bursa trans-tendinous (2 injections), and (4) OI bursa short-axis (2 injections). In each case, the operator injected 1.5 mL of diluted yellow latex using direct sonographic guidance and a 22-gauge, 87.5-mm (3½-in) needle. Seventy-two hours later, study coinvestigators dissected each specimen to assess injectate placement.

Results: All 10 OI region injections accurately placed latex into the primary target site. Two of the 4 OI tendon sheath injections produced overflow into the underlying OI bursa. Both OI intramuscular injections delivered 100% of the latex within the OI. All 4 OI bursa injections (2 trans-tendinous and 2 short-axis) delivered 100% of the latex into the OI bursa, with the exception that 1 OI bursa trans-tendinous injection produced minimal overflow into the OI itself. No injection resulted in injury to the sciatic nerve or gluteal arteries, and no injectate overflow occurred outside the confines of the OI or its bursa.

Conclusions: The results of this investigation demonstrate that sonographically guided injections into the OI or its bursa are feasible and, therefore, may play a role in the diagnosis and management of patients presenting with gluteal and "retrotrochanteric" pain syndromes.