Comparison of curved and straight tip radiofrequency cannula deflection in a ballistic model

Percutaneous pain and spine procedures play an important diagnostic and therapeutic role in the treatment of various pain diagnoses. Accurate placement of needles or cannulae during these procedures is paramount to the success of these procedures. The purpose of this study is to examine and quantify the amount of deflection of radiofrequency cannulae based on curved tip versus no curved tip, using a ballistic gel tissue simulant. Six different types of cannulae commonly used for spinal and peripheral nerve ablations were selected, including 18, 20, and 22 gauge curved and straight radiofrequency cannulae. Ballistic gel samples were made in molds of 40 mm and 80 mm. Each cannula was mounted in a drill press to ensure accurate trajectory. Curved RFA cannula had increased deflection when compared to straight cannula for 18-, 20-, and 22-gauge cannulae at a depth of 40 mm. Curved RFA cannula had increased deflection when compared to straight cannula for 20- and 22-gauge cannulae at a depth of 80 mm. Overall, the mean deflection for a curved cannula increased 1.9x for 20-gauge cannulae and 2.5x for 22-gauge cannulae when compared to a straight cannula. For interventionalists, understanding the effects of needle or cannula shape is crucial for accurate placement. When a procedure requires additional steerability, additional deflection up to 2.5x obtained by placing a bend in the needle or cannula tip should be considered.