We have previously studied intraarticular (IA) analgesics compared with saline 10 mL in 2 randomized clinical trials. The patients who were given IA saline experienced rapid pain relief. Hypothetically, saline may produce a local analgesic effect by cooling or by diluting IA algogenic substances. This randomized double-blind study compared the analgesic effect of IA saline 10 mL with saline 1 mL, which should be a pure placebo. A soft catheter was left IA in 79 patients. We included 60 patients who developed moderate-to-severe pain within 1 h after knee arthroscopy under general anesthesia. A randomized, double-blind controlled comparison of IA saline 10 mL with saline 1 mL followed. Outcome measures were pain intensity, pain relief, and analgesic consumption. Within 1 h pain intensity decreased in both groups from approximately 50 to approximately 27 on a 0-100 mm visual analog scale. Pain intensity remained low and other pain outcome measures were similar during the 36-h observation period. The patients experienced equally good pain relief after IA injection of saline 10 mL and 1 mL. Our finding of a major placebo effect may have implications for the interpretation of previously published placebo-controlled IA analgesia studies.
Implications: In a randomized controlled trial we showed that pain after knee arthroscopy is modest and short-lived and can successfully be treated with intraarticular saline as placebo.