The Shamrock sign. Sonographic model image of transmuscular quadratus lumborum (TQL) block. Anatomy relevant for the execution of the TQL block. The needle is inserted in plane to the curvilinear probe and advanced through the quadratus lumborum (QL) muscle to reach the interfascial plane(▲, local anesthetics) between the QL and psoas major (PM) muscles. Injectate spreads in the interfascial plane and depresses the PM muscle. TP, transverse process; PM, psoas major; QL, quadratus lumborum muscle; ES, erector spinae; EO, external oblique muscle; IO, internal oblique muscle; TA, transversus abdominis muscle