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Fig. 9.22 The psoas major is the major supporting guy-wire
between the spine and the leg, joining upper to lower, breathing to
walking, and acting with other local muscles in complex ways for
steadying various movements.
Fig. 9.24 The femoral triangle, the leg's equivalent to the armpit,
opens from the anterior septum between the sartorius (A) and the
adductor longus (B). It passes, with the psoas (C), iliacus (D),
pectineus (E), and neurovascular bundle (not pictured), under the
inguinal ligament (F) into the abdominal cavity. The psoas, iliacus,
and pectineus form a fan reaching up from the lesser trochanter to
the hip bone and lumbar spine. Length and balanced tone in this
complex is essential for structural health and freedom of
movement. (© Ralph T Hutchings. Reproduced from Abrahams et
al 1998.)
The psoas muscle, also clearly a hip flexor and also
variously described as a medial or lateral (or, as this
author has been persuaded, a non-) hip rotator, is even
more mired in controversy in terms of its action on
the spine (Fig. 9.25). 4 This author is convinced, through
clinical experience, that the psoas should be considered
as a triangular muscle, with differing functions for the
upper psoas, which can act as a lumbar flexor, and
the lower psoas, which clearly acts as a lumbar extensor.
If this differentiation of function is valid, the lumbars
can be fully supported by balancing the various slips
of the psoas with the post-vertebral multifidi, without
reference to the tonus of the abdominal muscles
(again, see 'The Psoas Pseries' 3 ).
Fig. 9.23 There are four 'gullies' around the spine; the erector
spinae muscles in the back and the psoas in the front fill in these
gullies and support the lumbar vertebrae.
Psoas express and locals
inguinal ligament into the trunk. The iliacus is a one-
joint flexor of the hip, equivalent in some ways to the
subscapularis in the shoulder. The iliacus is definitely
and obviously a hip flexor, though there is some contro-
versy over whether it is a medial or lateral rotator of the
hip (see 'The Psoas Pseries' 3 ).
We have said that multi-joint express muscles often
overlie other monarticular locals. In the case of the psoas
muscle, there are two sets of locals that serve the same
area, but here they lie on either side of the express
instead of underneath it (Fig. 9.26). While there is con-
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