The effects of experience on the inter-reliability of osteopaths to detect changes in posterior superior iliac spine levels using a hidden heel wedge.
Sutton C, Nono L, Johnston RG, Thomson OP. J Bodyw Mov Ther. 2013 Apr;17(2):143-50.
One cannot assume that a 5 mm heel lift will raise the ankle mortise and the hip by 5 mm since the height of the plantar metatarsals from the ground is not increased by a heel wedge.
It is more likely that a 5 mm heel wedge should lift the ankle mortise and the hip by about 4 mm due to the increased slope of the plantar foot to the ground that such a heel lift would create.
They appear to be defining sacral dysfunction in one plane as well, sagitally. Can the STJ be defined as dysfuntional solely in the sagittal plane? (no is the correct answer btw). Add to this you can have sacroilliac symptoms without a difference in height of the PSIS.