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psoas major muscle (anatomy)
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Psoas major is one of the muscles of the posterior abdominal wall and anterior thigh. It arises from several sites:

  • vertebrae bodies of T12 to L5
  • vertebral transverse processes of L1 to L5
  • intervertebral discs of T12 to L5

It passes as a thick, fusiform muscle inferolaterally along the pelvic brim. Deep to the inguinal ligament it inserts into the medial surface of the lesser trochanter of the femur. Within the thigh it joins with the iliacus muscle to form the functional unit of the 'iliopsoas muscle'.

Psoas acts to:

  • flex and medially rotate at the hip joint
  • flex the vertebral column anteriorly
  • flex the lumbar vertebral column laterally