Background: Spinal manual therapy is used by physiotherapists to produce relief of pain of musculoskeletal origin. In addition to the reported biomechanical effects of this treatment modality, recent research has revealed a complex neurophysiological response follows its application. It has been hypothesized that the potential locus of control for this response is the periaqueductal gray region of the midbrain and associated structures. The columnar structure of this supraspinal centre produces modulation of pain by 2 mechanisms, opioid and non-opioid accompanied by responses of a number of other systems including the sympathetic nervous system and motor system. The response is dependent on the column stimulated and the nature of the stimulation. It is postulated that part of the initial response to spinal manual therapy is coordinated by the lateral column of the periaqueductal gray, while persistent hypoalgesic
response may be produced by the ventrolateral column. Research of other therapeutic stimulation such as acupuncture and TENS has demonstrated that the nature of the response to stimulation changes depending on the parameters of the stimulation (eg duration, frequency). The major aim of this thesis is to further elucidate the characteristics of the hypoalgesia that follows spinal manual therapy and to determine if the nature of the response changes over time. The qualities of the response could provide further indication of the mechanism by spinal manual therapy produces pain relief.
Methods: This thesis consists of 4 randomised, controlled within-subjects studies utilising both asymptomatic (Study II - Chapter 6) and symptomatic subjects (Studies I, III and IV - Chapters 5, 7 & 8). Lateral epicondylalgia was used as a model of chronic musculoskeletal pain. Both pain related and sympathetic nervous system related
measures were used as outcome measures in all studies except for Study II in which only sympathetic nervous system related measures were collected. The treatment technique used in the studies was a lateral glide technique at C5-6. In Study I, the effect of application of the technique over a number of sessions was investigated. In the second study, response over time to different doses of the technique was examined. In Study III pain and sympathetic nervous system related responses were measured at 1-hour after manual therapy or control applications to determine the presence of a persisting hypoalgesic effect. Study IV examined the characteristics of this later response.
Results: Application of the lateral glide technique at C5-6 resulted in an initial hypoalgesic effect accompanied by excitation of the sympathetic nervous system. This effect was reproduced across all studies.
The effect did not appear to be decreased by repeated application of the technique (Study I). The hypoalgesic effect was seen to persist for up to 1-hour after the application of treatment and this effect was accompanied by sympathetic nervous system excitation. This later hypoalgesic effect was significantly larger than that produced by manual contact and no contact control conditions (Study III) and was not reversible by the opioid antagonist, naloxone (Study IV). The sympathetic nervous system responses were predominantly excitatory immediately after the technique and either returned to baseline values or continued to exhibit excitatory responses after the application of technique (Studies II, III & IV). This effect was independent of the dose of technique applied (Study II).
Conclusion: The application of the lateral glide treatment technique at C5-6 produces a consistent response of
hypoalgesia and sympathetic nervous system excitation. It appears that the stimulation to the central nervous system produced by spinal manual therapy, results in a similar set of responses which appear to persist over time is not dependent on the parameters investigated in this thesis. It is therefore postulated that spinal manual therapy may activate supraspinal structures that control the coordinated response of a number of systems in particular the lateral column of the midbrain periaqueductal gray and associated structures. Further investigations are now required to more directly test this hypothesis.