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Other Terms: Lumbodorsal fascia, Investing fascia of back, Lumbar fascia, Fascia thoracolumbalis, Fascia thoraco-lombal
The thoracolumbar fascia is the name given to the investing fascia of the body wall musculature in the dorsal aspect of the trunk. In the thorax it forms the dorsal investment of the epaxial and serratus posterior superior muscle and separates these muscles from the limb muscles that project onto the dorsum of the trunk. It attaches to the spinous processes medially and the angle of the ribs laterally where it converges with the investing fascia of the hypaxial thoracic wall. It continues into the lumbar region where it has three distinct laminae that converge laterally at the aponeurosis of the transversus abdominis muscle. The posterior lamina of the fascia sits deep to the superior limb muscles that pass onto the dorsum of the trunk and invests the serratus posterior inferior muscle and the epaxial muscles from the lumbar region to the back of the sacrum. It attaches to the spinous processes medially. The middle lamina of the fascia attaches to the bottom of the twelfth rib, the transverse processes of the lumbar vertebrae, and the iliac crest. It covers the anterolateral aspect of the epaxial muscles and merges with the posterior lamina at the lateral aspect of the iliocostalis muscles. The anterior lamina of this fascia attaches to the anterior aspect of the lumbar transverse processes and the iliolumbar ligament. It passes along the posterior aspect of the psoas major muscle and across the anterior surface of the quadratus lumborum muscle to join with the other laminae at the lateral border of the quadratus lumborum. It is thickened at the top of this muscle as the lateral arcuate ligament.