Thoracolumbar Fascia Middle Layer

fascia thoracolumbalis (lamina media)

The middle layer of the thoracolumbar fascia lies between the erector spinae and the quadratus lumborum, attaching medially to the lumbar transverse processes and laterally to the iliac crest. It forms the lateral raphe with the posterior layer and provides a fascial compartment for the lateral lumbar muscles.

Anatomical Data

Boundaries & Contents

Location	Lower back, between erector spinae and quadratus lumborum
Boundaries	Medially: tips of the lumbar transverse processes and the intertransverse ligaments Below: iliac crest Above: twelfth rib and the lumbocostal ligament Laterally: lateral raphe, where it receives the aponeurosis of transversus abdominis
Contents	Erector spinae behind it Quadratus lumborum in front of it

Biomechanics

Function & Actions

Separates the erector spinae from quadratus lumborum and gives the posterior attachment of transversus abdominis.

Clinical Relevance

Clinical Notes

The middle thoracolumbar fascial layer is disrupted during transforaminal lumbar interbody fusion (TLIF) and posterior lumbar approaches that require lateral retraction. Its disruption allows the erector spinae to shift laterally, reducing their mechanical advantage. In quadratus lumborum syndrome, dysfunction of the middle fascial layer alters force transmission between the lumbar spine and the iliac crest.

Pathology

Common Injuries & Conditions

Thoracolumbar Middle Layer Disruption

Fascial compartment disruption during posterior lumbar surgery or direct lateral lumbar trauma, contributing to post-operative erector spinae atrophy and altered lumbopelvic force transmission.

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