Knee joint mobilization reduces secondary mechanical hyperalgesia induced by capsaicin injection into the ankle joint

Joint mobilization is a treatment approach commonly used by physical therap ists for the management of a variety of painful conditions. However, the cl inical effectiveness when compared to placebo and the neurophysiological me chanism of action are not known. The purpose of this study was to establish that application of a manual therapy technique will produce antihyperalges ia in an animal model of joint inflammation and that the antihyperalgesia p roduced by joint mobilization depends on the time of treatment application. Capsaicin (0.2%, 50 mul) was injected into the lateral aspect of the left ankle joint and mechanical withdrawal threshold assessed before and after c apsaicin injection in Sprague-Dawley rats. Joint mobilization of the ipsila teral knee joint was performed 2 h after capsaicin injection for a total of 3 min, 9 min or 15 min under halothane anaesthesia. Control groups include d animals that received halothane for the same time as the group that recei ved joint mobilization and those whose limbs were held for the same duratio n as the mobilization (no halothane). Capsaicin resulted in a decreased mec hanical withdrawal threshold by 2 h after injection that was maintained thr ough 4 h. Both 9 and 15 min of mobilization, but not 3 min of mobilization, increased the withdrawal threshold to mechanical stimuli to baseline value s when compared with control groups. The antihyperalgesic effect of joint m obilization lasted 30 min. Thus, joint mobilization (9 or 15 min duration) produces a significant reversal of secondary mechanical hyperalgesia induce d by intra-articular injection of capsaicin. (C) 2001 European Federation o f Chapters of the International Association for the Study of Pain.