Disc degeneration can range from annular teat to frank herniation. While disc herniation can produce nerve-impingement symptoms, annular tears can be painful for both chemical and mechanical reasons. Release of noxious chemicals from the injured discs can cause chemical neuritis of adjacent nerves and produce sciatica that is clinically indistinguishable from compressive radiculopathy.
MRI not only is not sensitive in revealing annular tears, it provides no clue as to their clinical significance when they are seen.
Discograms are performed by injecting discs in question with dye under pressure, simulating mechanical stress. These provocative injections, with patients reporting pain levels during pressurization help separate painful from non-painful discs. Intradiscal dye and post-discogram CT further help to improve diagnostic accuracy. Discograms are particularly useful in evaluating patients for surgeries such as fusion and artificial discs.[/three_fourth_last]