A systematic review of the peripheral analgesic effects of intraarticular morphine

The analgesic effects of intraarticular morphine are controversial. To syst ematically evaluate the effects, we performed a review of the literature an d a metaanalysis of the peripheral effects of morphine injected intraarticu larly. Research databases were searched to identify articles in which perip heral analgesic effects of morphine were studied in patients undergoing art hroscopic knee procedures under local, regional, or general anesthesia. The review was performed on three issues: does morphine injected intraarticula rly produce analgesia, is it a dose-dependent effect, and, if so, is the ef fect systemic or mediated via peripheral opioid receptors? Visual analog sc ore (VAS) and analgesic consumption were studied during the early phase (0- 2 h), intermediate phase (2-6 h), and late phase (6-24 h) postoperatively a fter injection of morphine intraarticularly. Metaanalysis of these effect v ariables was performed by the weighted-analysis technique, and the essentia l homogeneity assumption was tested by the chi (2) test. Forty-five article s could be identified in which the effects of morphine were studied in a pr ospective, randomized manner, and 32 of these studies included a placebo co ntrol. Pooled analyses of data from 19 studies suitable for metaanalysis sh owed an improvement in analgesia after morphine compared with placebo in th e order of 12-17 mm on the VAS during all three phases of treatment. Studie s with high quality scores showed somewhat smaller improvements. Total anal gesic consumption could not be analyzed statistically, but the number of st udies showing decreased analgesic consumption or no differences between gro ups was identical (six and six). No clear dose-response effect was seen whe n VAS was used as a measure of pain, but it was seen when area under the cu rve was used as a measure of pain. A systemic effect of peripherally-inject ed morphine was not possible to exclude because of the very limited data av ailable. We conclude from this metaanalysis that intraarticularly administe red morphine has a definite but mild analgesic effect. It may be dose depen dent, and a systemic effect cannot be completely excluded.