Reproducible piriformis injection methodology by fluoroscopic and electromyographic guidance

Introduction. Injection of the piriformis muscle is commonly used to treat Piriformis Syndrome. While some published approaches have been described, including "blind"1, image guided, and electrophysiologic2 methods, there is not a single uniform technique that has validated exact placement of the needle tip within the piriformis muscle. We describe a technique that combines fluoroscopy and electromyography (EMG). This approach offers electrophysiologic confirmation of needle placement within the piriformis muscle by EMG demonstration of motor unit action potentials and radiographie, anatomic identification of the piriformis muscle with radiopaque contrast media. Methods. Patients with "piriformis syndrome" underwent injections of the piriformis muscle under fluoroscopic guidance (Philips BV 300) with contrast agent and EMG. Injection was performed with subjects in the prone position after sterile preparation and dressing. Fluoroscopically, the expected position of the piriformis muscle was identified by landmarks consisting of the greater trochanter and lateral border of the sacrum on the affected side. The injection site was superficial and posterior to the ilium and superior and medial to the acetabulum. The needle (22 gauge 75 mm Myoject monopolar electrode needle) was placed at approximately 1/3 the distance along the posterior gluteal line from the medial border of ilium just superior to the medial intersection of the ilium and ischium. It was passed until reaching bone (Image 1). Subjects were asked to externally rotate and slightly abduct the hip resulting in piriformis muscle activation. While the piriformis muscle was activated, the needle was gradually retracted under EMG guidance (TECA TD 20 with settings of 2Hz low frequency filter and 200 mv per division) until evidence of motor unit action potentials were demonstrated. At the point of maximal motor unit activity, non-ionic contrast media (2 cc iopamidol 61%, Isovue 300) was injected, resulting in a myogram demonstrating contrast spread outlining the piriformis muscle in a characteristic pattern spanning from the lateral boarder of the sacrum to the acetabulum and, less frequently, to the greater trochanter. This characteristic pattern of spread (Images 2 and 3) was found in all cases using this technique (n = 12). Piriformis needle placement with fluoroscopic guidance alone, without EMG, was unreliable. Final confirmation was made by AP, lateral, and oblique fluoroscopic views and EMG tracings. Discussion. Use of EMG demonstrates that the injection site is within muscle while contrast agent spread demonstrates that the muscle is piriformis. This methodology offers precise documentation of needle placement within the piriformis muscle which is reliable, relatively uncomplicated, and reproducible.