An exploration of the physiological effects of spinal manipulation in patients with low back pain

Spinal manipulation (SM) is effective in reducing back pain, despite poor understanding of the physiological mechanisms by which it exerts its effect. There is some evidence of a biomechanical effect whereby joint 'gapping' stretches the joint capsules and weak evidence of a reflex muscular response. In terms of the latter it is far from clear whether this reflex is attributable to a SM and is not just a result of general movement or other non-specific effects nor whether it is associated with any therapeutic effect. SM is thought to be associated with an anti-algesic effect, although no previous work has considered which element of manipulation might be responsible for this or whether the effect changes with repeated applications. This thesis attempts to address some of these questions and in particular focuses on the reflexogenic and anti-nociceptive effects of SM. Method: To address this knowledge deficit, highlighted by a review of the current literature, a single blind pilot randomised controlled trial was designed in order to explore the physiological effects of SM. After testing for reliability of a number of the outcome measures and research to establish the specific dysfunctional spinal segment, 60 patients were randomised to receive a single high velocity low amplitude thrust or a sham manipulation of the lumbar spine. Physiological effect, in a number of muscle groups was explored through assessment of pressure pain threshold (PPT) and muscle activity using algometry and surface electromyography (sEMG). The sEMG reflex response, and a record of whether cavitation was achieved, was recorded during the manipulation. Other more subjective assessments of pain were also measured (visual analogue scale (VAS) and Roland Morris questionnaire). The intervention was repeated on three separate occasions over three weeks to test for a dose related response. Results: There was no statistically significant difference in the magnitude of the sEMG reflex response to a single SM, but at the third application a significantly larger sEMG reflex response was seen in the SM group, compared to the sham manipulation (for multifidus and gluteus maximus). There were no associations between the size of the reflex response and any of the subject's baseline characteristics or changes in pain at any time point. There was a significant increase in the PPT ofthe local spinal muscles in the SM group compared to the sham manipulation group, although this was mainly seen at the first treatment. There were no significant differences in the VAS or Roland Morris questionnaire scores between groups over the course of the experiment. There were no statistically significant differences in any of the pain measures if the groups were split according to whether the SM resulted in cavitation. Discussion and conclusion: It is unlikely SM influences pain and function via a muscular reflexogenic effect. It may be that the longitudinal change in the reflex response is indicative of a biomechanical change in one group. This study lends further support to the theory that SM has an anti-nociceptive effect, however this is only seen as a local effect (changes in PPT) and is therefore most likely to be at a spinal level. Specific application of the thrust to a clinically relevant spinal segment, seems to be the most important factor to achieve therapeutic benefit, irrespective of whether this resulted in cavitation. SM seems to have local specific effects on pain (evoked by mechanical stimulation) but little effect on disability or overall pain statesEThOS - Electronic Theses Online ServiceGBUnited Kingdo