When is sciatica NOT derived from irritations at the intervertebral joint level?, rarely. Sciatica , for the most part , is a neuralgic event , brought about by protective activity at the spine. For a fuller description of "protective responses", go to Rehabedge and look in the manual therapy section . This activity may or may not have anything to do with pathology, is most often related to dysfunction rather than disease. The old ( now largely discredited) notion that sciatica is a product , mostly , of disc disease , has taken a battering over the past few years.
If in your dissertation , you make mention of the most likely causes with emphasis, that is , inflammatory events of nerve roots at the effect of protective activity at or near spinal facet joints. You will be offering a consideration and understanding rare in your treatment community , but in keeping with the emergence of a quiet revolution in thinking about musculoskeletal pain and dysfunction.