Abstract
Diagnostic blocks are used to identify patients with back pain stemming from their lumbar zygapophysial joints. Single, diagnostic blocks have an unacceptably high false positive rate. As well, comparative local anaesthetic blocks lack validity because the prevalence of the condition is low. Relying on 50% relief following single-diagnostic blocks does not provide a valid diagnosis. Placebo-controlled blocks are the only available valid means of establishing a diagnosis of lumbar zygapophysial joint pain.