The double fulcrum effect during ultrasound-guidedparavertebral block

The double fulcrum refers to the points at which the angle of the ultrasound needle is limited by both the edge of the ultrasound transducer, and separately, by the edge of the transverse process. The solid line labeled A represents a shallow needle path that facilitates needle visualization, but because of the double fulcrum the needle cannot be advanced into the paravertebral space. A steeper needle trajectory allows entry into the space, but needle visualization is less optimal. If this occurs, either slide the transducer cephalad to the point at which the caudad TP is just barely in view, switch to a smaller footprint curvilinear transducer, or switch to an oblique transducer orientation.