Amitabh Gupta, Brad Fernihough, Glen Bailey, Petra Bombeck
Introduction
The iliopsoas (IP) muscle has an undisputed action of flexing the hip joint (Skyrme, Cahill, Marsh, & Ellis, 1999), however psoas major (PM) has a controversial role in other actions on the lumbar spine; as a prime mover or stabiliser (Adams, Bogduk, Burton, & Dolan, 2002). A requirement of ideal turnout position (180°) in ballet requires extreme hip external rotation (ER) which causes an abnormal anatomical alignment of the lower extremity (Bennell et al., 1999; Bowling, 1989). Musculotendinous imbalance was identified as one of five risk factors that aimed to screen dancers (Micheli, 1983). The IP muscle is a structure that is implicated in the pathophysiology of these injuries, as it plays a vital role in the arthrokinematics of the dancer with connections from the thoracolumbar fascia to the lower extremity (Prather, 2000). Although muscle size and strength are age and sex specific (Hanson, Magnusson, Sorensen, & Simonsen, 1999) and dissection may not represent the structure and function in the dancer’s hip, further investigation of the anatomy will provide an understanding of the structures’ susceptible to pathology.
In light of the possible role of IP as a lumbar stabiliser, investigation of the muscle structure, fasicule orientation and origin, will elucidate the ability of the IP to perform a stabilising role at the lumbar spine. The lower segments of the PM have been previously described as irregular and feeble (Bogduk et al., 1992; King, Hine, McDonald, & Abrahams, 1993). Interestingly, the maximum cross-sectional area for the PM has been observed at the L4/5 level (J. G. Reid, 1994). . The question arises as to whether these lower lumbar segments can generate a hip flexion torque and/or act as a stabiliser, while maintaining the alignment of the tendinous upper portion (Bogduk et al., 1992; King et al., 1993).
