Analgesic effect of intra-articular morphine after arthroscopic knee surgery

Objectives: To assess the analgesic effect of intra-articular morphine. To establish the optimal dose of morphine as well as the best volume of solution to obtain an adequate analgesic effect. Patients and methods: Prospective, randomized, double blind study of 120 patients undergoing elective arthroscopic meniscectomy. Patients were randomly allocated to one of the following five groups: In group A1 (n=28) and B1 (n=20) patients received 1 and 5 mg of intra-articular morphine, respectively; in both groups morphine was diluted in 20 ml of saline. Another two groups, groups A2 (n=22) and B2 (n=26) received 1 and 5 mg of intra-articular morphine, respectively, that was diluted in 40 ml of saline. Finally, the control group, group C (n=26), received 20 ml of saline without morphine. The intensity of the pain was evaluated by visual analog scale of 1 to 10 points at 30 min and at 1, 2, 3, 6, 12 and 24 h after arthroscopic surgery. Needs for complementary analgesia and side effects related to morphine were also recorded. Results: With respect to the control group there was a significant improvement in pain scores in those patients that were treated with morphine (p<0.05). The best morphine dose to improve pain was 5 mg. The amount of analgesic therapy required by the patients within the first 24 h after surgery was lower in groups B1 and B2. No important side effects or complications of therapy were seen in any of the groups. Conclusions: Intra-articular morphine is effective in the postoperative period after arthroscopic meniscectomy. This method of administration provides a safe way to control the postoperative pain after arthroscopic ambulatory surgery of knee. In our experience a morphine dose of 5 mg disolved in 20 ml of saline constitutes the best therapeutic approach to reduce postoperative pain after arthroscopic meniscectomy.