Background: Manual therapy has been used commonly in the treatment of musculoskeletal pain. Its efficacy in pain relief has been documented in a number of meta-analyses and systematic reviews. However, little information has been established on its mechanism of action.
Preliminary investigation of the mechanisms underlying the pain relieving effect of spinal manual therapy (SMT) has shown that it produces concurrent hypoalgesic and sympathoexcitatory effects. These concomitant effects (ie., hypoalgesia and sympathoexcitation) are like those of stimulation-produced analgesia of the midbrain periaqueductal gray, leading to the proposition that manual therapy induces hypoalgesia through a control mechanism in this pain modulatory centre (chapter 3). However, this proposed mechanism of action has yet to be tested on treatment techniques other than those applied to the spine, especially in the peripheral joints. If this hypothesis is to be considered as generic to all manual therapy, further study is required on techniques other than the limited number of SMT techniques studied previously. The main aim of this thesis
was to investigate the neuro-biological characteristics of Mulligan's mobilisation-with-movement, a recently developed manual therapy approach.
Methods: A total of 90 subjects who had unilateral, chronic lateral epicondylalgia (chapter 4) participated in 4 separate studies of the neuro-physiological effects of a mobilisation-with-movement treatment technique applied to the elbow (MWME). A randomised, double blind, placebo-controlled, crossover, repeated measures study design was utilised in 3 of the 4 studies. The dependent variables consisted of various pain-related measures (ie., pain-free grip strength, pressure pain threshold, thermal pain threshold, upper limb neural tissue provocation test 2b) and sympathetic nervous system indicators (ie., heart rate, blood pressure, cutaneous blood fluxes, skin temperature, skin conductance).
Results: Hypoalgesic and sympathoexcitatory effects occurred initially post-application of the MWME for treatment of chronic lateral epicondylalgia, and these treatment effects (ie., hypoalgesia and sympathoexcitation) were significantly
greater than that of placebo and control conditions (chapters 5 to 6). Moreover, the hypoalgesic effect produced by MWME was not significantly antagonised by an opioid antagonist, naloxone (chapter 7, section 7.1). Magnitudes of hypoalgesic effect did not decrease with repeated treatment applications over 6 successive sessions (ie., hypoalgesia did not demonstrate tolerance), adding to the findings that MWME induced hypoalgesia was not opioid mediated (chapter 7, section 7.2).
Conclusion: The studied peripheral manual therapy treatment technique (MWME) appears to have a similar effect profile to the previously studied spinal manual therapy techniques. At least in part its pain relieving effect is more likely to involve a non-opioid mechanism of action. Its neuro-physiological effects demonstrate immediate and concurrent changes in hypoalgesia with sympathetic activation, paralleling the feature of a descending pain inhibitory system initiated by stimulation of the
lateral-dorsal periaqueductal gray region. Further work is now required to continue to evaluate this proposed mechanism of action.