quadratus lumborum
noun
quadratus lum·bor·um
| \ -ləm-ˈbȯr-əm
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Medical Definition of quadratus lumborum
: a quadrilateral-shaped muscle of the abdomen that arises from the iliac crest and the iliolumbar ligament, inserts into the lowest rib and the upper four lumbar vertebrae, and functions especially to flex the trunk laterally