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The dermatomal level of analgesia achieved with quadratus lumborum blocks varies according to the location of injection. The most commonly used approaches are either at the postero-lateral aspect or anterior to the quadratus lumborum muscle.To determine whether the site of injection of contrast dye around the quadratus lumborum muscle of cadavers affects the extent and mechanism of dye spread.Observational human cadaver study.Cleveland Clinic cadaveric laboratory.Six fresh human cadavers.The cadavers received either a posterior quadratus lumborum block or an anterior subcostal quadratus lumborum block on each side.Cadavers were dissected to determine the extent of dye spread.The posterior quadratus lumborum block approach revealed consistently deep staining of the iliohypogastric, ilioinguinal, subcostal nerve, T11 to 12 and L1 nerve roots. In addition, staining of the middle thoracolumbar fascia was seen in all specimens but only variable staining of T10 nerve roots. The anterior subcostal quadratus lumborum block approach in all specimens demonstrated predictable deep staining of the iliohypogastric and ilioinguinal nerves, subcostal nerves, T11 to 12 and L1 nerve roots, and in addition traversing the arcuate ligaments to involve T9 to 12 nerve roots with variable staining of higher thoracic nerve roots.Our cadaveric study demonstrates that injection of dye on the posterior aspect of quadratus lumborum muscle led to injectate spread through the lateral and posterior abdominal wall but with limited cranial spread, whereas the anterior approach produced broader coverage of the lower to mid-thoracic region. Clinical translation of these findings to determine the practical significance is warranted.