Primary functions of the quadratus femoris and obturator externus muscles indicated from lengths and moment arms measured in mobilized cadavers.

Background: The small muscles of the pelvis and hip are often implicated in painful conditions. Although the quadratus femoris and obturator externus are usually described as external rotators of the hip, little is known about how they change their lengths and moment arms during human movement. Therefore, more precise measurements defining the positions and directions for their maximal strength and stretch are needed to better describe their functions and guide the clinical approach to pain.

Lengths of the external hip rotators in mobilized cadavers indicate the quadriceps coxa as a primary abductor and extensor of the flexed hip.

Background: The primary function of the external rotators of the hip is inadequately described. The descriptions for peak strength and stretch take no account of how these muscles change their length during normal movement. The latter relationship is known to greatly influence contraction forces and reflect moment arms.