BJA Advance Access originally published online on July 9, 2004
British Journal of Anaesthesia 2004 93(3):375-380; doi:10.1093/bja/aeh222
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© The Board of Management and Trustees of the British Journal of Anaesthesia 2004
Increased numbers of opioid expressing inflammatory cells do not affect intra-articular morphine analgesia
1 Abteilung für Anaesthesiologie und Intensivmedizin, LKH Klagenfurt, St. Veiter-Straße 47, A-9020 Klagenfurt, Austria. 2 Klinik für Anaesthesiologie und Operative Intensivmedizin, Charité–Universitätsmedizin Berlin, Campus Benjamin Franklin, Hindenburgdamm 30, D-12200 Berlin, Germany. 3 Abteilung für Traumatologie, LKH Klagenfurt, Klagenfurt, Austria. 4 Klinik für Anaesthesiologie, Schmerzambulanz, Universität Erlangen-Nürnberg, Erlangen, Germany
* Corresponding author. E-mail: micha.schaefer{at}charite.de
Background. Both locally expressed ß-endorphin (END) and low doses of morphine relieve pain within inflamed knee joints. Here we examined whether enhanced inflammation and END expression within the synovial tissue of patients undergoing arthroscopic knee surgery might shift the analgesic dose–response curve of intra-articular (i.a.) morphine.
Methods. Following IRB approval and informed consent, patients were randomly assigned to the following i.a. treatments at the end of surgery: group I (n=39), isotonic saline; group II (n=40), 1 mg morphine hydrochloride; group III (n=48), 2 mg morphine hydrochloride; group IV (n=39), 4 mg morphine hydrochloride. Postoperative pain intensity was assessed by the visual analogue scale (VAS), by the time to first analgesic request and by the supplemental piritramide consumption. Synovial specimens from each patient were stained for the presence of inflammatory cells and END and were discriminated into groups with low versus high numbers of these cells. Differences between groups were statistically analyzed by 
2, ANOVA and MANCOVA where appropiate.
Results. Patient characteristics and VAS scores did not differ between groups. Total postoperative piritramide consumption decreased and the time to first analgesic request increased significantly with increasing doses of i.a. morphine (P<0.05, ANOVA and linear regression). These dose–response relationships were not different between patients with low versus high numbers of inflammatory and END-containing synovial cells (P>0.05, MANCOVA).
Conclusions. The dose–response relationship of i.a. morphine analgesia is not shifted by enhanced inflammation and END expression within synovial tissue. Thus, the presence of END within inflamed synovial tissue does not seem to interfere with i.a. morphine analgesia.
Some of the results were presented in abstract form at the Annual Meeting of the Society of Anesthesiology (ASA), San Francisco, CA, 2000.
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