Is Saline Injection a True Sham/Placebo Treatment in Randomized Controlled Trials? A Systematic Review

Objective: To explore whether saline is a real sham/placebo agent, or it has potential therapeutic effects when used as control treatment in randomized controlled trials for the management of discogenic low back pain. Methods: A comprehensive literature search was conducted investigating the effects of saline as a placebo in the treatment of chronic pain when administered into the intervertebral disc. Following stepwise filtering, selected articles were assessed for their levels of evidence, followed by a discussion of their contribution to the understanding of the role of saline in chronic pain management. Results: Out of 95 articles that described the administration of intradiscal saline solution used as a placebo for chronic pain management, 8 articles met all of the inclusion criteria. Their levels of evidence ranged from 1a to 4 (Oxford Centre CEBM). Intradiscal administration of saline solution was found to have measurable therapeutic benefits. In some studies, the pain relief was similar to that provided by local anaesthetics and steroids. Conclusion: Although the exact mechanism of the analgesic effects of saline is not clear, yet the use of intradiscal saline appears to have some analgesic benefits like local anaesthetics and steroids when used individually. Researchers should practice caution when designing RCTs using intradiscal saline injection as a sham/placebo treatment for the control arm or maybe, when possible, avoid the use of intradiscal saline injection as a sham treatment.