Analgesic effects of indirect moxibustion on an experimental rat model of osteoarthritis in the knee.

AIMS The analgesic effects of moxibustion on an experimental model of osteoarthritis of the knee were investigated. METHODS Male Wistar rats (n=36, 296-421 g) were used. Intra-articular injection of mono-iodoacetic acid (MIA) was performed to induce knee osteoarthritis. Indirect moxibustion was applied to the lateral aspect of the knee joint every other day for 28 days (14 treatments). Weight bearing of the hind legs was measured directly by the downward pressure applied to footplates, using an Incapacitance Tester. Morphine was injected for testing the validity of weight bearing as a pain measure, and naloxone was used to examine the participation of endogenous opioids in the mechanism of moxibustion analgesia. Data were analysed by calculating the area under the curve. RESULTS Injection of MIA significantly reduced weight bearing. No analgesic effects of moxibustion were observed during the initial 7 days (unpaired t test, P=0.83). Continued moxibustion treatments increased weight bearing at the 14th day significantly, and this effect continued until the end of the experiment on the 28th day (P<0.05). A single moxibustion treatment had no immediate effect on weight bearing. The analgesia due to the cumulative effect of moxibustion was antagonised by naloxone injection. Morphine injection in control MIA injected rats increased weight bearing to the normal range, confirming the validity of the measurements. CONCLUSIONS These results highlight the importance of repeated moxibustion treatments for pain relief in experimental knee osteoarthritis and suggest the existence of sustained inhibitory modulation by endogenous opioids in the moxibustion group.