Analgesic effect of intraarticular morphine. A controlled, randomised and double-blind study

Background: Opioids produce antinociceptive effect by acting on receptors on peripheral nerves. The clinical relevance of this effect is still debated. The aim of the study was to compare the analgesic effect of morphine intraarticularly with the intramuscular route of administration after knee surgery. Methods: Sixty-one patients, ASA 1-2, having elective arthroscopic surgery of the knee were randomised to either an intraarticular or intramuscular dose of morphine 5 mg. The pain sensation was estimated by visual analogue scale and a verbal rating score 0, 1, 2 and 4 hours postoperatively and verbal rating score on the third day. The use of acetaminophen and supplementary opioids were recorded for the first 4 hours postoperatively, from 4 hours until the third day, and from day 3 to day 7 postoperatively. Results: The groups were comparable. Three patients were excluded. There were no statistically significant differences in painscore and consumption of analgesics. Fifty-nine per cent in each group had macroscopic synovitis. In the intraarticular group, there was no increased effect of morphine in the patients with synovitis compared to patients without synovitis. Conclusions: The clinical analgesic effect of 5 mg morphine given intraarticularly is equal to 5 mg morphine given intramuscularly. The occurrence of villous synovitis seems to be of no clinical importance concerning the local effect of morphine.