Effects of interfascial injection of bicarbonated Ringer’s solution, physiological saline and local anesthetic under ultrasonography for myofascial pain syndrome -Two prospective, randomized, double-blinded trials-

Abstract

Myofascial pain syndrome (MPS) is a common clinical condition of muscle pain. Previous studies indicated that local injection of physiological saline (PS) into a muscle is equal to or more effective than a local anesthetic for MPS. We performed 2 randomized, double-blinded trials of interfascial injection under ultrasonography for outpatients with MPS over 3 months to assess the effects of PS (pH 6.0), 0.5% mepivacaine hydrochloride (MH) (pH 6.0), and bicarbonate Ringer’s solution (BRS) (pH 7.4), and to elucidate their action mechanisms. Maximum pain related to motion, time of pain relief, and pain related to injection (intensity and duration) were measured up to 72 hrs. The first trial showed that PS decreased maximum pain related to motion compared to MH (p < 0.05), although it increased pain related to injection compared to MH (p < 0.05). The second trial showed that BRS exhibited as much efficacy in relieving maximum pain related to motion as PS (p = 0.33), but decreased pain related to injection compared to PS (p < 0.05). In conclusion, the interfascial injection of PS has a greater analgesic effect on MPS but produced stronger pain related to injection compared to MH. BRS is equivalent to PS in analgesic effect and produced less pain related to injection compared to PS. These results indicate that BRS is the appropriate solution for an interfascial injection to treat MPS, and that the action mechanisms are not related to the pain intensity associated with the injections or the pharmacological anesthetic effect