A cadaver study comparing spread of dye and nerve involvement after three different quadratus lumborum blocks

Background: Posterior variants of abdominal wall block include the quadratus lumborum type I, quadratus lumborum type II and quadratus lumborum transmuscular blocks. Our objectives were to compare the spread of injectate and nerve involvement after conducting blocks using ultrasound guidance in soft embalmed cadavers.Methods: After randomisation, an experienced anaesthetist conducted three quadratus lumborum 1, three quadratus lumborum 2 and four transmuscular blocks on the left or right sides of 5 cadavers. All cadavers were placed in the lateral position and the quadratus lumborum muscle visualised using a 3 to 9MHz ultrasound probe placed in the flank. For each block, a 20ml mixture of 17.75ml water, 2mls latex and 0.25ml India ink was injected. The lumbar region and abdominal flank were dissected 72 hours later. Results: We conducted 10 blocks. Two quadratus lumborum 1 and two quadratus lumborum 2 blocks were associated with spread of dye within the TAP plane. One quadratus lumborum 1 block spread to the deep muscles of the back and one quadratus lumborum 2 block dispersed within the subcutaneous tissue surrounding the abdominal flank. All transmuscular quadratus lumborum blocks spread consistently to L1 and L3 nerve roots as well as within psoas major and quadratus lumborum muscles.Conclusions: Consistent spread to lumbar nerve roots was achieved using the transmuscular approach through the quadratus lumborum