The arcTOA Technique for Out-of-Plane Ultrasound-Guided Injections

Out-of-plane (OOP) ultrasound-guided injections are often cited as being more difficult than in-plane ultrasound-guided injections, particularly for the novice ultrasonographer. In certain circumstances, the OOP approach is required as a result of the constraints of adjacent anatomic structures. To date, only the “walk-down” approach has been detailed in the literature as a means of improving accuracy with the OOP approach. However, this approach uses a set needle entry angle (angle of incidence) and distance for the injection. This article uses the trigonometric function, arctan = opposite/adjacent (arcTOA), to allow readers to easily estimate the needle angle of incidence (arcTOA technique), allowing more flexibility when planning and performing OOP injections.