Question
In the chiropractic model, when an SIJ "flexion fault" or an "extension fault" is named what does the fault define?  Is this the position it is restricted in or is this the position it is not moving into?  Is it reference to the sacrum or the ilium?

Answer
Sandra,

Thank you for your question.

Nomenclature regarding musculoskeletal dysfunction varies considerably, depending upon the practitioner and the system or technique used in patient evaluation and treatment.

I am unfamiliar with the terminology you have mentioned; my educated guess is that a sacro-iliac joint "flexion fault" describes a restriction (or inability) of the SI joint to nutate (or move along a rotational axis) in the forward-bending (or flexion) range of motion, and an "extension fault" probably relates to the opposite restriction of backward-bending range of motion.

Typically, a S.I. joint dysfunction descriptor identifies the restricted range of motion of the ilium relative to the sacrum, but when speaking about the joint itself, the entire motion unit is considered as a whole, rather than speaking about one static bone.

Regardless of the particular nomenclature used, in my opinion, the most important factors with regard to sacro-iliac joint dysfunction are whether or not the SI joint can be identified as the predominant generator of pain and whether the manipulative or rehabilitative techniques being used are helpful in reducing the patient's symptoms.

I hope that this helps to answer your question.