['Intra-articular (IA) morphine for postoperative analgesia after knee arthroscopy is controversial. The IA catheter technique for test drug administration allows baseline pain assessment before inclusion. Results from one such randomized controlled trial (RCT) in patients with moderate to severe pain have shown equal effects of IA saline with or without morphine 2 mg. However, the IA catheter technique may have an unintended placebo effect. The aims of this placebo-controlled RCT were (1) to compare the analgesic effect of IA saline 1 mL (placebo) with morphine 5 mg given through an IA catheter and (2) to analyze the impact on pain of immediate or delayed removal of the IA catheter.', 'Sixty patients operated under general anesthesia had an IA catheter inserted at the end of arthroscopy. Patients who reported moderate or severe postoperative pain during the following hour were randomized to IA saline 1 mL (placebo) or IA morphine 5 mg and to immediate or delayed removal of IA catheter.', 'Forty of 60 patients (67%) developed moderate to severe pain within 1 hour. In addition, 5 patients experienced intolerable pain and were excluded. Significantly more women (24/26) than men (26/39) reported at least moderate pain (P = .018) during the first hour after surgery. There were no differences between IA morphine 5 mg and placebo in pain intensity or pain relief at any time during the 48-hour observation period. There was no detectable effect on pain intensity of early compared with late removal of the IA catheter.'] Does intra-articular morphine 5 mg after knee arthroscopy produce significant pain relief when administered to patients with moderate to severe pain via an intra-articular catheter?