Intra-articular morphine as analgesic in temporomandibular joint arthralgia/osteoarthritis

The aim of this study was to determine the analgesic efficacy of a single dose intra-articular injection (i.a.) of morphine in 53 patients with unilateral arthralgia/osteoarthritis of the temporomandibular joint (TMJ). This randomized, double-blind, parallel group, multicenter study included a screening visit, a treatment visit, and a follow-up visit 1 week after treatment. Recordings of visual analog scales (VAS) pain intensity scores at maximum mouth opening (main efficacy variable) and at jaw rest were made directly before a 1-ml i.a. injection into one TMJ of either 1.0mg morphine-HCl, 0.1mg morphine-HCl, or saline (placebo). The pain intensity was also recorded at the follow-up and in a diary 3 days before and 5 days after the injection. The VAS pain score at maximum mouth opening was considerably reduced 1-10h after injection but without significant differences between groups. At the follow-up, the median VAS pain score at maximal mouth opening was significantly lower in the 0.1-mg morphine group than in the 1.0-mg morphine group (P<0.043) or the saline group (P<0.021). A significant increase in pain pressure threshold over the affected joint was seen in the 0.1-mg morphine group compared with the saline group at the follow-up but not 1 and 2h post-injection. The incidence of adverse events was small and did not differ between the treatment groups. In conclusion, one i.a. injection of 0.1mg morphine significantly increased the pain pressure threshold and mouth opening ability, but evidence for the analgesic property of the locally applied opioid was inconclusive. No dose-effect relation and no significant short-term analgesic property were seen. Although statistically significant, the magnitude of the reduced VAS pain intensity score was not clinically relevant at the 1-week follow-up.