Dose-dependency of intra-articular morphine analgesia

We have examined if the analgesic effects of intra-articular morphine are d ose-dependent in patients undergoing elective arthroscopic knee surgery. At the end of surgery, patients were allocated randomly to one of four groups to receive intra-articular saline (n=22), or morphine I mg (n=24), 2 mg (n =21) or 4 mg (n=19). After operation, patients remained in hospital overnig ht and pain intensity was assessed using a visual analogue scale at 1, 2, 3 , 6, 9, 12, 18 and 24 h after intra-articular injection. Patients requestin g additional analgesia received a loading dose of piritramide 0.1 mg kg(-1) i.v. and were connected to a PCA device using the same drug. Increasing do ses of intra-articular morphine were associated with greater analgesic effe cts and less supplementary analgesic requirements.