Thoracolumbar fascia

The thoracolumbar fascia (lumbodorsal fascia or thoracodorsal fascia) is a complex,^: 1137 multilayer arrangement of fascial and aponeurotic layers forming a separation between the paraspinal muscles on one side, and the muscles of the posterior abdominal wall (quadratus lumborum, and psoas major^: 1137) on the other.^: 1137 It spans the length of the back, extending between the neck superiorly and the sacrum inferiorly. It entails the fasciae and aponeuroses of the latissimus dorsi muscle, serratus posterior inferior muscle, abdominal internal oblique muscle, and transverse abdominal muscle.

In the lumbar region, it is known as lumbar fascia and here consists of 3 layers (posterior, middle, and anterior) enclosing two muscular compartments. In the thoracic region, it consists of a single layer (an upward extension of the posterior layer of the lumbar fascia). The thoracolumbar fascia is most prominent at its lower end^{: 814–815} where its various layers fuse into a thick composite.