Spinal manual therapy produces rapid onset analgesia in a rodent model

Jane E. Grayson, Tom Barton, Peter J. Cabot, Tina Souvlis

A rapid hypoalgesic effect following spinal manual therapy (SMT) has been demonstrated in humans. Although the characteristics of the pain relief are well described, the mechanisms have remained speculative. The purpose of this suite of studies was to investigate the effects of SMT on pain measures using animal models. This study employed a randomized, controlled design. Study 1: Rats without inflammation were allocated to either a treatment group (n = 6) that received three applications of joint mobilization centrally over L5 or a sham-treated group (n = 6) who received non-specific handling. Pressure pain threshold (PPT) and thermal pain threshold (TPT) were measured before and immediately after each intervention. Results demonstrated significantly increased mechanical nociceptive thresholds in the SMT group (p = 0.01) compared to that of the sham-treated group but no difference for thermal nociceptive thresholds. Study 2: The time course effect of an inflammatory and mechanical response following i.pl injection of inflammatory mediators was investigated to determine the appropriate time period for a treatment intervention. Study 3: The effects of SMT on mechanical nociception were investigated following interplanar injection of inflammatory mediators into the right hind paw of rats as a pain model (n = 6 for both SMT and sham-treated groups). Injection of endogenous metabolites produced significant swelling and flaring as well as increased PPT values following SMT (p < 0.02) compared with controls. These results demonstrate a rapid analgesic response following application of SMT, which has similar characteristics as that seen in both symptomatic and asymptomatic human populations.