Calculation way of pelvic asymmetry

Description

・ PAR = |right ASsh − left ASsh|/horizontal distance ASIS − ASIS + |right PSsh-left PSsh|/horizontal distance PSIS-PSIS

a) ASsh, anterior superior iliac spine height

b) PSsh, posterior superior iliac spine height

Advantages:

This formular correct the shortcoming of dimensions of the pelvis by divided by horizontal distances ASIS-PSIS, and would not be influenced by the difference between the anatomical sides and dominant sides.

Disadvantages:

The result of formula cannot provide judgement about which kind of asymmetry of the pelvis has shown.

・ PAIS = ∠S_D − ∠S_ND

a) ∠S_D, angle between ASIS-PSIS line in the dominant side and z-axis

b) ∠S_ND, angle between ASIS-PSIS line in the nondominant side and z-axis

PAIS = 0, perfect symmetry of the pelvis;

PAIS > 0, larger posterior rotation/extension of the innominate in the dominant side;

PAIS < 0, larger posterior rotation/extension of the innominate in the nondominant side.

・ PAIF = (∠FA + ∠FP)/2

a) ∠FA, angle between R-L ASIS line and x-axis

b) ∠FP, angle between R-L PSIS line and x-axis

PAIF = 0, perfect symmetry of the pelvis: lines R-L ASIS and R-L PSIS are parallel to the x-axis or the angles between them and x are identical but opposite;

PAIF > 0, higher left innominate;

PAIF < 0, higher right innominate.