Quadratus lumborum, means “the square muscle in the low back.” It connects the lumbar vertebrae to the ribs and iliac crest trapping T12 and the sacrum its attachments.
Quadratus Lumborum has 3 sections; iliolumbar, lumbocostal and lateral. They perform different functions, have different trigger point patterns and are best addressed as different muscles.
Quadratus lumborum varies dramatically in dissection studies. The size, as well as the shape of each belly, have statistically significant variations. The muscle appears the be thinner medially with a thicker lateral belly in most cases. The quadratus shown in most illustrations, like this one, depict a healthy decompression of the low back. In mature adults, the lumbar vertebrae and lumbocostal space are usually compressed.
Electromyographical show that it is active in several functions; lateral flexion of the trunk, elevation of the hip, extension of the lumbar spine, forced exhalation, trunk rotation, brisk walking.
It is worth noting that the iliolumbar ligament develops from the immature fibers of the quadratus lumborum during the adolescent years and atrophies when the sacroiliac joint fuses in the 4th or 5th decade.
The iliolumbar section connects the crest of the ilium to L1-L4 trapping the sacrum and L5 between them. It is located posteriorly to the other sections.
The lumbocostal section connects the transverse processes of all the lumbar vertebrae to the medial half of the 12th rib, trapping T12 in between. It is the most anterior section.
The lateral section connects the central portion of the 12th rib to the iliac crest trapping the sacrum and T12-L5 between them.
Here’s a structural overview from The Neuromuscular Assessment Guides.SO-quadratus-lumborum
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