Dr. Kevin Yip

Dr Kevin Yip
Orthopaedic Surgeon
MBBS(UK), FRCS(EDIN), FAM(SING), FHKCOS(ORTHO)

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Anatomy of The Lumbar Back Muscles-Transversus Abdominis

The TrA is the deepest muscle of the abdominal muscle complex, with the internal and external oblique being more ventral and the rectus abdominis in the center with a fascial envelope encased with a bilaminar aponeurosis. The TrA is the deepest muscle of the abdominal muscle complex, with the internal and external oblique being more
ventral and the rectus abdominis in the centre within a fascial envelope encased with a bilaminar aponeurosis.

The TrA originates from the “lateral one-third of the inguinal ligament, the anterior two-thirds of the inner lip of the iliac crest, the lateral raphe of the thoracodorsal fascia, and the internal aspect of the lower six costal cartilages interdigitating with the costal fibers of the diaphragm.

The muscle runs transversely around the trunk where its upper and middle fibers bend with the fascial envelope of the rectus abdominis. Superior to the umbilicus, the aponeurotic fibers of the transversus abdominis pass posterior to the rectus abdominis in either [a] superior or an inferior direction to blend with aponeurotic fibers of contralateral transversus abdominis and internal oblique.

Below the umbilicus, all of the aponeurotic fibers run inferiorly with the anterior laminae passing anterior to the rectus abdominis and the posterior laminae passing posterior to the rectus abdominis. Caudally, the posterior laminar fibers gradually pass anterior to the rectus abdominis along with the anterior laminar fibers” . The TrA has stabilizing and respiratory functions.

With contraction of the TrA, a drawing in or hollowing of the abdominal wall occurs, which produces tension of the thoracolumbar fascia through the lateral raphe and increased abdominal pressure.

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