Location and Borders
The fascia is located in the back and lumbar regions, enclosing the deep back muscles and lying adjacent to the erector spinae muscle (m. erector spinae). At the level of the upper thoracic vertebrae, it appears as a thin sheet, gradually thickening toward the lumbar region, and transitions into a dense aponeurosis at the lower thoracic level.
Medially, the superficial layer attaches to the spinous processes of the thoracic and lumbar vertebrae, the sacrum, and the iliac crest; laterally, it attaches to the angles of the ribs. Inferiorly, the axillary fascia (fascia axillaris) transitions into the thoracolumbar fascia.
Internal Structure and Layers
The fascia consists of two layers that participate in forming the sheath for the deep back muscles:
- Superficial (posterior) layer — attaches medially to the spinous processes of the thoracic and lumbar vertebrae, sacrum, and iliac crest, and laterally to the angles of the ribs. At the lateral border of the erector spinae muscle, it fuses with the deep layer.
- Deep (anterior) layer — extends from the transverse processes of the lumbar vertebrae to the 12th rib and superiorly. In the lumbar region, it forms a fibrous sheath for the deep muscles; laterally, it fuses with the quadratus lumborum and intertransverse muscles.
At the lateral border of the m. erector spinae, both layers unite to form a fibrous muscular sheath. Anteriorly from this fusion point originates the aponeurosis of the transversus abdominis muscle.
Functions and Muscular Attachments
The thoracolumbar fascia strengthens the posterior wall of the trunk and participates in the transmission of mechanical forces.
Muscles associated with the fascia include:
- Deep back muscles, which are located deep to the fascia thoracolumbalis;
- Erector spinae muscle (m. erector spinae), enclosed within the aponeurotic sheath formed by the fascial layers;
- Gluteus maximus muscle (m. gluteus maximus), which originates from the thoracolumbar fascia;
- Latissimus dorsi muscle (m. latissimus dorsi): the fascia fuses with the fascia of the latissimus dorsi and forms a compartment for it in the lumbar region;
- Internal oblique muscle (m. obliquus internus abdominis), which arises from the fascia thoracolumbalis at the site of fusion of its layers;
- Transversus abdominis muscle (m. transversus abdominis), which arises from the deep layer of the fascia thoracolumbalis.
Clinical Significance in Surgery
The fascia is clinically important during retroperitoneal surgical approaches, such as the Fedorov incision (lumbar approach / lumbotomy). During this approach, tissues are divided layer by layer, including the fascia thoracolumbalis and m. quadratus lumborum. Subsequently, the parietal peritoneum along with adipose tissue is bluntly dissected medially and superiorly, the kidney is palpated through the fascia, the fascia is incised, the adipose capsule is bluntly dissected, and the kidney is mobilized into the surgical wound.