Innominate segment deformation during passive hip abduction and external rotation.

Background: Electromagnetic palpation-digitization technique for measurement of innominate motion involves calculation of innominate rotation using the innominate vector length in the neutral (NEUT) and combined hip abduction and external rotation (HABER) test positions. The innominate vector length [i.e., the segment between anterior superior iliac spine (ASIS) and posterior superior iliac spine (PSIS)] is not a rigid structure and its deformation could introduce an error influencing the final innominate rotation measurement.

Objectives: The aim of this study is to determine if there is significant deformation occurring in innominate vector length when the hip is loaded into the HABER test position.

Method: A cross sectional study using sixteen healthy individuals and a single tester was conducted. Four pelvic landmarks, left and right PSIS and ASIS, were palpated and digitized using 3D digitizing stylus of Polhemus electromagnetic tracking device, in two hip test positions, NEUT and 50° HABER. The innominate vector lengths were calculated from the 3D coordinates of pelvic landmarks, for each hip test positions.

Results And Conclusion: Paired t-tests demonstrated no significant differences (p > 0.05) in the innominate vector lengths at the side of the load as well as the opposite innominate when either the right or left hip was loaded; thus indicating no significant bone deformation in innominate segment during the HABER test position.