Pressure Pain Thresholds and Basal Electromyographic Activities Following Spinal Mechanical Manipulation
Condition: Pain
Study type: Interventional

Summary: 
      The purpose of this study is to investigate if the application of spinal mechanical
      manipulation on low back region resulted in changes in pressure pain thresholds (PPT) in
      asymptomatic subjects and the extent of the hypoalgesia; whether it is local, regional or
      systemic. Simultaneously, the investigators are to further explore the phenomenon of reduced
      sEMG activity after spinal mechanical manipulation to better understand the immediate effects
      of mechanical manipulation on low back region.
    

Detailed description: 
      Spinal manipulation (SM) is used by clinicians for the treatment of several chronic pain
      conditions. The effectiveness of different spinal manipulations targeted at the lumbar spine
      in patients with low back pain is supported by an increasing number of high-quality
      randomized clinical trials1and systematic reviews. Although these techniques have shown some
      effectiveness in clinical practice, most of clinical studies solely investigated the effects
      of spinal manipulation on overall reports of pain and function and the underlying mechanisms
      by which manipulation produce clinical effects remain largely unknown.

      The neurophysiologic mechanisms by which manipulation inhibits pain, however, are matters of
      speculation and still under investigation. Proposed hypotheses have suggested that
      manipulation has the potential to remove the source of mechanical pain or induce
      stimulus-produced analgesia. Spinal manipulation induces sufficient force to simultaneously
      activate both superficial and deep somatic mechanoreceptors, proprioceptors, and nociceptors.
      The effect of this stimulation is a strong afferent segmental barrage of spinal cord sensory
      neurons, capable of altering the pattern of afferent input to the central nervous system and
      inhibiting the central transmission of pain. Other suggested mechanisms have been the
      activation of the endogenous opiate system, the alteration of the chemical mediators or the
      effects of joint cavitation. An understanding of the mechanism by which manipulations cause a
      hypoalgesic response is subject to further research and is currently far from complete. A
      review of the literature found several studies exploring immediate changes in mechanical pain
      sensitivity provoked by spinal manipulative procedures. Mobilisation/manipulation to the
      cervical spine has been shown to provide a hypoalgesic effect as measured by pressure pain
      thresholds (PPTs) in patients suffering from mechanical neck pain and lateral epicondylalgia.
      A hypoalgesic effect has also been demonstrated following mobilization to peripheral joints
      in the upper and lower limbs. Mobilizations to the lumbar spine have been shown to produce an
      immediate and significant widespread hypoalgesic effect in asymptomatic subjects However,
      Perry et al. that found unilateral mobilizations on the lumbar spine respectively had side
      specific response.

      Besides analgesic effect, it has been presented spinal manipulation can reduce the increased
      resting muscle tone or spasm, which can be monitored by surface electromyography (sEMG). If
      the presence of a hypertonic muscle is functionally associated with a spinal dysfunction that
      is correctable by SM, it would consequently follow that the associated higher EMG level would
      diminish after appropriate SM. In a descriptive study DeVocht JW et al. found that
      manipulation induces an immediate change, usually a reduction, in resting EMG level in
      patients with low back pain. Herzog J reported the observation of a single but very dramatic
      decrease in resting EMG activity in thoracic musculature within 1 second of SM. One possible
      segmental mechanism could be that the manipulation may induce a reflex muscle relaxation by
      modifying proprioceptive group 1 and 2 afferents. However, few randomly controlled trials
      have directly investigated the effect of spinal mechanical manipulation on basal
      electromyographic activity (BEA) in asymptomatic subjects.

      Spinal mechanical manipulation has been widely used in clinical manual therapy. However,
      because mechanical thrusts usually produce no cavitations, whether mechanical techniques
      produce the same hypoalgesic effects and muscle relaxation as manual techniques remains
      untested. To further elucidate the physiologic mechanisms associated with spinal mechanical
      manipulation, it is essential to investigate its effects in asymptomatic individuals who do
      not have any active central sensitization. In fact, recent studies have supported the use of
      asymptomatic subjects in studies related to neurophysiological mechanisms of spinal
      manipulations. Further research is therefore required to clarify if there is a hypoalgesic
      effect or muscle relaxation in response to spinal mechanical manipulation in the lumbar
      region in asymptomatic subjects.
    

Intervention name(s): Spinal mechanical manipulation intervention; Sham manipulation intervention
Intervention type(s): Other; Other
Intervention description(s): Subjects in experimental group are assessed through use of the Activator Methods (AM) assessment protocol. Spinal adjustment of the indicated pelvis, sacrum and lumbar spine is performed through the use of spinal mechanical manipulation. In this study leg length analysis only uses Position #1 and Position #2. Mechanical manipulation is delivered with the Activator Ⅳ Adjusting Instrument (AAI Ⅳ; Activator Methods International, Ltd, Phoenix, AZ) set in the maximal force setting 4, as it is used in routine clinical practice. The Activator Ⅳ delivers a very short duration (<5 ms) force-time impulse with a peak force magnitude of approximately 176N.; Subjects in the control group receive a protocol identical to that described above, with the following exception: a sham mechanical thrust is delivered during the AM protocol. The sham procedure is accomplished by setting the expansion control knob on the Activator Ⅱ to the zero (off) position. The expansion control is used to adjust the spring compression and thus the amount of excursion of the instruments' stylus. In the zero position, no excursion of the stylus occurs, although the same clicking sound that the instrument produces during normal use is heard after manual activation of the mechanical trigger.
Other intervention name(s): Activator methods maximal setting; Activator methods zero setting
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: Double (Participant, Outcomes Assessor)
Primary purpose: Treatment
Keywords: Spine; Manipulation; Pain Threshold; Electromyography.