(from 15°–45°); and (3) as an effective flexor of the lower
extremity at the hip joint (from 45°–60°). They further
concluded that the function of the psoas major as a hip
stabilizer is overshadowed by its action of stabilizing/
erecting the lumbar vertebral column.
Over the last decade, new insights into muscle function
and the role of muscles in providing dynamic stability
have emerged. Some muscles may have stabilization of
the lumbosacral spine as their primary role, while others
appear to have multiple roles and these multiple roles may
be dependent upon spinal position and the loads being
transmitted to the spine (i.e. low load vs. high load).25–27
Recent research on lumbar musculature and how it relates
to individuals suffering from lower back pain has
progressed through the use of advanced imaging techniques.
Dangeria and Naesh28 conducted a clinical prospective
cohort study examining the cross-sectional area
of the psoas major in healthy volunteers and subjects with
unilateral sciatica caused by a disc herniation. These authors
demonstrated that in most patients with a lumbar
disc herniation there was a significant reduction in the
cross-sectional area of the psoas major on the affected side
only and most prominently at the level of the disc herniation.
They suggested that a correlation exists between the
reduction in the cross-sectional area of the psoas major
(Spearmann’s rho = 0.8; P = 0.05) and the duration of continuous
sciatica of the affected side but that no correlation
exists between the amount of disc herniation and reduction
in psoas major cross-sectional area. Similarly, Danneels et
al.29 examined the trunk muscles (paraspinal, psoas and
multifidus) in chronic low back pain patients and healthy
control subjects employing computerized tomography at
three different lumbar levels. These authors found no significant
differences in the cross-sectional area of the psoas
major or paraspinals but they did find significant differences
existed in the cross-sectional area of the multifidus
at the L4 spinal level. Barker et al.30 investigated the crosssectional
of the psoas major in the presence of unilateral
low back pain through the utilization of magnetic resonance
imaging (MRI). These authors found that there were
statistically significant differences in cross-sectional area
of the psoas major between sides (median reduction was
12.3%) at the levels of L1-L5 and that there was a positive
correlation between a decreased cross-sectional area of
the psoas major and the duration of symptoms. In another
MRI study, Hides et al.31 assessed the effects of prolonged