Clinical studies of discography in asymptomatic subjects or discs with or without a history of spine surgery were eligible for inclusion. Studies that reported numerical ratings of pain intensity, concordancy, pain behaviours, pressure or degree of anular disruption and which reported data for a control disc, were eligible for inclusion. Studies of older discographic techniques (including noxious dyes) were excluded from data analysis and synthesis. Mean age of participants ranged from 22.6 to 46.5 years. All studies except one were conducted in majority male populations.
Abstracts of retrieved studies were assessed against inclusion criteria. Full articles were obtained if the criteria were met. Three physicians assessed studies for inclusion, but the selection process was not reported (for example, it was unclear whether all physicians examined all studies).