Sex differences in the pattern of innominate motion during passive hip abduction and external rotation

The objective of the study was to evaluate sex differences in the pattern of innominate motion about the sacroiliac joint (SIJ) during hip movement. Although the magnitude of intrinsic SIJ motion is influenced by joint congruence and ligament elasticity sex differences in pelvic joint kinematics are under-investigated. Forty healthy and active males and females between the ages of 18 and 35 were recruited. 3D motion of the innominate bones and femur were recorded with a magnetic tracking device as the hips were loaded in standardised increments of 10 degrees in 3 positions - external rotation (ER), abduction (AB), and combined external rotation and abduction (AB+ER). While females had greater overall innominate motion, two distinct sex dominant patterns emerged. Patterns of innominate motion also differed when load was applied to the dominant rather than non-dominant limb. As the main motion within the pelvis is intrinsic, the results of the present study point to a differing viscoelastic response and different movement strategies to passive load between the sexes. In addition, careful attention to limb dominance should be considered when testing SIJ motion.