With the posterior, what does the middle thoracolumbar fascia enclose?

With the posterior, what does the middle thoracolumbar fascia enclose?

• A. Quadratus lumborum
• B. Psoas major
• C. Latissimus dorsi
• D. Deep back muscles

Answer: (D)

The key idea is that the thoracolumbar fascia has three layers that compartmentalize the muscles of the back and flank. The middle layer forms a fascial envelope around the quadratus lumborum, a thick muscle running along the lumbar region from the iliac crest to the 12th rib and lumbar vertebrae. This muscle sits between the posterior layer (which covers the deep back muscles like the erector spinae) and the anterior layer (which surrounds the psoas major). Latissimus dorsi, though it attaches to the thoracolumbar fascia, is not contained within the middle layer’s compartment. Therefore, the middle thoracolumbar fascia encloses the quadratus lumborum.

The key idea is that the thoracolumbar fascia has three layers that compartmentalize the muscles of the back and flank. The middle layer forms a fascial envelope around the quadratus lumborum, a thick muscle running along the lumbar region from the iliac crest to the 12th rib and lumbar vertebrae. This muscle sits between the posterior layer (which covers the deep back muscles like the erector spinae) and the anterior layer (which surrounds the psoas major). Latissimus dorsi, though it attaches to the thoracolumbar fascia, is not contained within the middle layer’s compartment. Therefore, the middle thoracolumbar fascia encloses the quadratus lumborum.