The fascial relations of the psoas major to the surrounding tissues warrant special attention as these links influence the biomechanics of these interlaced structures. The medial arcuate ligament is a continuation of the superior psoas fascia that continues superiorly to the diaphragm. The right and left crus constitute the spinal attachment of the diaphragm. They attach to the anterolateral component of the upper three lumbar vertebral bodies.The crus and their fascia overlap the psoas major and appear to be continuous with this muscle until they come more anterior and blend with the anterior longitudinal
ligament.8 As the psoas descends, its inferomedial fascia
becomes thick at its inferior portion and is continuous
with the pelvic floor fascia.9 This forms a link with the
conjoint tendon, transverse abdominus, and the internal
oblique.10 As the psoas major courses over the pelvic
brim, the fascia of the posterior fascicles attach firmly to
the pelvic brim.