Psoas major and its controversial rotational action

The action of psoas major muscle as a primary flexor of the hip joint is un disputed. However it is also variably reported as being a medial and a late ral rotator of the femur at the hip joint. The psoas and iliacus muscles, a long with their common insertion, were isolated by dissection in six adult cadaveric specimens. The action of psoas muscle was assessed by pulling the muscle along its long axis and then observing the effects on rotation of t he femur, with a visual estimation of the rotation in degrees. The experime nt was repeated with the hip joint capsule removed. In the anatomical position, applied traction along the long axis of the mus cle produced hip flexion with no rotational component. With the hip in the abducted position, traction produced flexion, adduction, and lateral rotati on of the femur at the hip joint. In adduction of the hip, traction on psoa s produced only flexion at the hip joint, with no rotation. In maximal flex ion, traction also produced adduction. The results were unaffected by the r emoval of the joint capsule. (C) 1999 Wiley-Liss, Inc.