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Lumbosacral manipulation & MEP
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“The effect of Lumbosacral Manipulation on Gastrocnemius Motor
Evoked Potential’s using Transcranial Magnetic Stimulation.”
Students: Claire Richardson (B.Sci.) Shaun Richardson (B.Sci.)
Kymberley Sayers (B.Sci), Melanie Taylor (B.Sci), Nicholas Wittenberg (B.Sci)
Supervisors
Dr. Gary Fryer
Dr. Alan Pearce
Osteopathic Medicine Unit
School of Biomedical & Health Sciences
Victoria University
June 2010
Submitted for consideration as a research proposal for the Master of Health Science (Osteopathy)
minor thesis
Lumbosacral manipulation & MEP
TABLE OF CONTENTS
Glossary of terms…………………………………………………………………………….....4
1. Introduction……………………………………………………..…………………………...9
2. Literature Review………………………………………………..………………………….11
2.1 Lumbosacral manipulation in osteopathy…………………………........................11
2.2 Theories for therapeutic mechanisms associated with HVLA……………………13
A) Studies involving spinal manipulation and H-Reflex
B) Studies involving spinal manipulation reflex muscular activity
2.3 Effects of HVLA………………………………………………………………….15
A) Range of motion
B) Hypoalgesia
C) Other neurophysiological effects
2.4 Motor evoked potentials……………………………………………………………21
2.5 Summary…………………………………………………………………………...23
3. Aim………………………………………………………………..…………………………26
4. Methodology………………….………………………….…………………………………..27
4.1 Participants…………………………………………………………………………27
A) Inclusion Criteria
B) Exclusion Criteria
4.2 Experimental Design………………………………………………………………28
4.3 Procedure………………………………………………………………………….28
A) Measurement of MEP
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B) Intervention
i. HVLA
ii. Control Group
4.4 Statistical Analysis…………………………………………………………………29
5. Ethics……………………………………………………..……………………………….....30
6. Timeline……………………………………….……………………………………………..32
7. Budget…………….……………………………………….…………………………….......33
8. References…………………………………………………………………………………...34
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Lumbosacral manipulation & MEP
GLOSSARY OF TERMS
Afferent Fibre – a nerve fibre that carries impulses toward the central nervous system
Alpha Motoneuron – lower motor neurons of the brainstem and spinal cord which innervate
extrafusal muscle fibres of skeletal muscle and are directly responsible for initiating their
contraction
Analgesia – Absence of pain in response to stimulation which would normally be painful
Axon hillocks – the anatomical part of a neuron that connects the cell body (the soma) to the
axon
Cavitation – the term used to describe the formation of gaseous bubbles or cavities within the
synovial fluid of the joint, as a result of distraction that causes local reduction in pressure
Central – see Central Nervous System
Central Nervous System – pertaining to the brain, cranial nerves and spinal cord. It does not
include peripheral nerves
Corticospinal – pertaining to the corticospinal tracts, which are the descending motor pathways
conveying motor signals from the brain to the periphery
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Cerebral Cortex – The extensive outer layer of gray matter of the cerebral hemispheres, largely
responsible for higher brain functions, including sensation, voluntary muscle movement, thought,
reasoning, and memory
Dendrite – a branching process off a cell which receives signals and information from other
cells
Dorsal horn – the posterior horn of grey matter of the spinal cord. It receives several types of
sensory information from the body, including light touch, proprioception, and vibration
Efferent Fibre– a nerve fibre that carries impulses away from the central nervous system
Epicondylitis – inflammation of the muscles and soft tissues around an epicondyle
Facilitated Segment – facilitated segment is a concept that is proposed to explain the behaviour
of somatic dysfunction: an injured somatic or visceral structure produces a barrage of discordant
afferent impulses into the dorsal horn of the spinal cord which "sensitises" that segment. It is
proposed the spinal interneuron thresholds are lowered, allowing an exaggerated response to
pathways synapsing at that level: increased pain perception, sympathetic outflow, and
segmentally supplied muscle tone
Lumbosacral manipulation & MEP
Facilitation – the effect of a nerve impulse acting across a synapse, resulting in increase
postsynaptic action potential of subsequent impulses in that nerve fibre or other convergent
fibres
H/Mmax ratio – The ratio of the. Maximum H-reflex to Maximum. M-wave
High Velocity Low Amplitude (HVLA) – a forceful, high-velocity thrust that stretches a joint
beyond its passive range of movement in order to increase its mobility. Manipulation is usually
accompanied by an audible pop or click
H-Reflex – the H-reflex is the electrical equivalent of the monosynaptic stretch reflex. It is
elicited by selectively stimulating the Ia fibers of the posterior tibial or median nerve
Hyperalgesia – increased sensitivity to painful stimuli
Hypoalgesia – decreased sensitivity to painful stimuli
Hypomobility – a decrease in the normal range of joint movement
Meniscoid – fold of tissue within a joint structure
Motoneuron Pool – all of the alpha motor neurons required to supply an entire muscle
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Motor Evoked Potential (MEP) – used to describe potentials obtained from muscles by the
simulation of motor structures in the central nervous system
Muscle spindle – sensory receptors situated within the muscle belly, which primarily detect
changes in muscle length
Neuron – a nerve cell. The basic unit of the nervous system, specialized for the transmission of
electrical impulses
Nociception – neurological detection of a painful stimulus
Periaqueductal Gray (PAG) – the gray matter located around the cerebral aqueduct of the
midbrain. It plays a role in the descending modulation of pain and in defensive behaviour
Radiolucent – in medicine; a part of a body or object which permits the passage of x-rays
without leaving a shadow on the film. Soft tissues are radiolucent, bones are not
Reflex – the body's automatic response to a trigger that involves nerve impulses being received
from our sense organs, passed into the spinal cord, and a responding message being sent out
straight away, without needing any input from the brain
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Somatic Dysfunction – impaired or altered function of related components of the somatic (body
framework) system: skeletal, arthroidal, and myofascial structures, and related vascular,
lymphatic, and neural elements
Spinal Manipulation – see HVLA
Spinal Segment – a division of the spinal cord containing a bilateral pair of nerve roots
Synapse – the functional membrane-to-membrane contact of the nerve cell with another nerve
cell
Transcranial Magnetic Stimulation (TMS) –is a non-invasive method of exiting neurons in the
cerebral cortex. Weak electric currents are induced in the tissue by rapidly changing magnetic
fields
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1. INTRODUCTION
High velocity, low amplitude techniques (HVLA) are widely used by manual therapists and
musculoskeletal practitioners, including Osteopaths, Physicians, Physiotherapists and
Chiropractors. There have been many theories as to what effects this treatment technique has on
various systems of the body, both locally and distally, as well as the effect on neurological
processing and central nervous system excitability. (Dishman et al, 2002) This study aims to
investigate the effect that HVLA techniques applied to the spine have on motor cortex
excitability as measured by motor evoked potentials.
There have been studies providing evidence that HVLA techniques produce an analgesic effect
by activation of the descending pain inhibitory pathways of the spinal cord, as well as activation
of Gate-control mechanisms in the dorsal horn of the spinal cord. (Pickar et al 2002, Melzack, R.
et al, 1965) However, conflicting evidence regarding the neurophysiologic effects of HVLA and
therefore muscle activity exists. Two studies have shown an increase in motor neuronal activity
following spinal HVLA techniques, (Dishman et al 2002, Dishman et al 2008).Conversely,
another study by the same author reported a decrease in motor neuronal activity (Dishman et al
2000). Both sets of results have theories as to how they may provide a resultant decrease in
related musculature hypertonicity. It has been theorised that an increase in central excitability
could decrease hypertonicity of related musculature by normalising the pain modulatory
mechanisms of the central nervous system. (Dishman et al 2008) If however, HVLA decreases
motor neuron excitability, it has been theorised that less noxious stimuli would be able to reach
the affected segment. (Dishman et al 2002) More definitive research would obviously lend
weight to one of these theories.
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Our study will use Transcranial Magnetic Stimulation (TMS) to produce Motor Evoked
Potentials (MEP’s) in the gastrocnemius musculature, which we shall measure pre and post
intervention (HVLA technique applied to the Lumbosacral junction.) MEP’s are a non-invasive
method of measuring motor cortex excitability. The study is based upon previous research by
Dishman et al 2002. We hope to provide clear results regarding the effect on central motor
excitability as influenced by HVLA technique applied to the lumbosacral junction.
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2. LITERATURE REVIEW
2.1 Lumbosacral manipulation in osteopathy:
Spinal manipulation, or High Velocity Low Amplitude (HVLA) technique, is a technique applied
by chiropractors, physiotherapists, osteopaths and physicians. The technique “involves placing
the joint (in this case spinal) in a locked position and applying a short, sharp thrust as precisely
as possible to a single joint level” (Greenman 2003) There are many theories for the
physiological mechanisms underlying how this technique may be of benefit to the patient, but
these mechanisms are still largely speculative. (Dishman et al 2008).
Authors of osteopathic texts claim that HVLA techniques, applied to various parts of the body,
can aid to reduce “TART” diagnostic findings within the affected tissues. The TART diagnosis
within the Osteopathic profession refers to a collection of clinical findings within a dysfunctional
tissue: tenderness, asymmetry, altered range of motion and tissue texture change. These
diagnostic findings are claimed to confirm the presence of a somatic dysfunction, a term relating
to the impaired or altered function of the musculoskeletal system. (Licciardone JC, et al 2005).
Gibbons and Tehan, 2006, have stated that HVLA techniques can aid in the treatment of clinical
findings such as; hypomobility, motion restriction, joint fixation, acute joint locking, motion loss
with somatic dysfunction, meniscoid entrapment, and adhesions.
Studies have indicated that HVLA techniques may, by way of stretching joint capsular
structures, ligamentous structures, discal structures and muscular structures, activate the diffuse
descending pain inhibitory pathways, supporting the theory that this technique provides an
analgesic effect. (Vicenzino B, ,et al 1998).
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Furthermore, HVLA techniques applied to the spine have been proven effective in the reduction
of low back pain, (Koes, B., et al 1996) as well as being proven effective in decreasing the
disability and pain levels of patients with chronic neck pain (Murphy, B et al 2009) There has
also been research indicating that HVLA treatment of athletes with neck pain was potentially
more effective than high dose analgesic medication. (Gunnar et al 2008).
The literature has reported that HVLA techniques appear to affect not just the joints being
manipulated, but the associated musculature, disc, ligamentous and tendinous structures.
There have been studies undertaken which indicate the usefulness of HVLA techniques in
reducing pain within the paraspinal musculature, as well as creating long lasting effects after
doing so. (Shambaugh P. 1987, Zhu Y, Haldeman et 1993.)
Also, HVLA has been hypothesised to reduce pain of a discal origin within the spine by
transiently reducing the pressure-peak observed in the posterior annulus (J.Y. Maigne et al
2003).
Authors have stated that the cavitation that occurs between the joint surfaces during
administration of a HVLA technique increases the plasticity of the joint capsule, hence
increasing joint motion. (J.Y. Maigne, et al 2003) This capsular stretching has also been
attributed to the inhibition of paraspinal muscle spasm. (Bogduk N,et al 1985) There have been
studies that have proven that continuous EMG activities of the adjacent multifidus muscle to the
Lumbosacral junction have been diminished after having a HVLA technique applied to the
Lumbo Sacral Junction. (Thabe H ;1986).
In addition to the specific findings regarding pain and function of patients after administration of
a HVLA technique, there is evidence that supports such reduction in pain and increase in
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function that patients were more likely to have improved psychological functioning and a
reduction in absenteeism from work. (Gunnar et al, 2008)
We know that the Lumbo-Sacral junction is where the nerve roots of the innervation to the
gastrocnemius muscle originate, (Phillips L.H. 1991) and as such wish to investigate the effect
that HVLA techniques have upon the MEP's measured within the muscle, facilitated at the
segment.
2.2 Theories for therapeutic mechanisms associated with HVLA
The monosynaptic Hoffmann Reflex (H-Reflex) is the electrically induced version of the spinal
stretch reflex, also known as the myotatic reflex. Eliciting the H-reflex involves electrical
stimulation of the Ia afferent fibres proximal to their origin in the muscle spindle, thereby
bypassing the muscle spindle. The stimulus travels in the Ia afferent fibres through the
motoneuron pool of the corresponding muscle to the efferent (motor) fibres. The H-reflex is an
estimate of alpha motoneuron (aMN) excitability when presynaptic inhibition and intrinsic
excitability of the aMNs remain constant. (Palmieri et al., 2004)
A) Studies involving spinal manipulation and H-Reflex:
An early study involving H-reflex changes following spinal manipulation was conducted by
Dishman et al., 2000. The study investigated the effect of lumbosacral manipulation versus
spinal mobilization on tibial nerve H-reflexes recorded from the gastrocnemius muscle. The
authors found that there was a significant decrease in the H/Mmax ratio measured 10 seconds
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after the spinal manipulation, which returned to baseline 30 seconds after the manipulation.
Dishman et al. published a paper in 2002 contrasting the different effects of cervical versus
lumbar spinal manipulation on the tibial nerve H-reflex recorded from the gastrocnemius muscle.
The authors found that the H/Mmax ratio was significantly depressed with respect to baseline
values for 60 seconds after the L5/S1 spinal manipulative procedure; however, the there was no
concomitant change after C5-6 spinal manipulation. This led them to conclude that SMT
inhibition of motoneuron activity involves a local segmental response rather than an integrative
central response.
Another study on the effects of H-reflex changes following sacroiliac joint manipulation was
conducted by Murphy et al., 1995. The study investigated H-reflex responses from the soleus
muscle after ipsilateral sacroiliac joint manipulation. The authors found that H-reflex amplitude
was significantly decreased in the ipsilateral leg (p < 0.001) post manipulation while there was
no significant alteration following the sham intervention or in the contralateral leg.
B) Studies involving spinal manipulation reflex muscular activity:
A number of papers have demonstrated the existence of reflex muscular activity following spinal
manipulation. An EMG study on reflex muscular responses to HVLA was published by (Herzog
et al., 1999). The study demonstrated a consistent and systematic reflex response both in muscles
local to the manipulated joint and also in more distant muscles. The estimated latency of the
reflex response was 50ms. (Symons et al., 2000) conducted a similar experiment using an
activator device to deliver the manipulation. More localized, mainly ipsilateral reflexes with a
latency of 4ms were noted. An additional study on the effect of activator induced thrusts was
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conducted on low back pain patients by (Colloca and Keller, 2001). This paper also
demonstrated reflex responses with a latency of 4ms and found that patients with the greatest
degree of pain and disability had the largest amplitude of reflex response
2.3 Effects of HVLA:
Spinal manipulation has been used for more than 2000 years (Evans, 2002). Manipulative
treatments have been recorded since Hippocrates in 400BC who wrote of their value in treating
spinal mal-alignment (Potter, McCarthy, & Oldham, 2005). Today spinal manipulation is used
by chiropractors, osteopaths, physiotherapists and some medical practitioners (Potter, et al.,
2005). Numerous theories have been proposed to explain the effects of spinal manipulation. A
common trend in these theories is that changes in the normal anatomical, physiological or
biomechanical dynamics of contiguous vertebrae can adversely affect function of the nervous
system. Spinal manipulation is thought to correct these changes (Picker, 2002). Overall the goal
off spinal manipulation is too restore maximal, pain-free movement of the musculoskeletal
system (Greenman, 1989)
A) Range of Motion:
Current research indicates that the range of motion of a joint increases after cavitation (Brodeur,
1995). In a study by Fritz, Whitman & Childs (2005) subjects with LBP who were judged to
have lumbar spine hypomobility experienced greater benefit from the manipulation
The greater mobility caused by manipulation can easily be explained by the increase in joint
volume as a result of the gas bubble formation within the joint (Brodeur, 1995). The change in
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joint volume associated with the crack must allow a greater range of motion; after cavitation the
joint capsule is not restricted by the volume of synovial fluid (Brodeur, 1995). The synovial fluid
offers little resistance to the force, and a temporary increase range of motion is given to the joint
(Evans, 2002).
Sandoz (Sandoz, 1976)performed a study looking at metacarpophalageal joint distractions, and
showed that distractions causing cavitation increased the radiolucent joint space. This was
associated with a 5-10deg increase in the range of movement of the joint once cavitaiton had
occurred. Meal & Scott (1986) and Conway et al (1993) have since performed studies looking at
the sounds from the metacarpophalageal joint distractions and compared them with the sounds
from facet joint cavitations in the spine. By comparing the sound waves they proposed, giving
the nature of the sound waves were similar in the finger distraction to the facet joint
manipulations, that a similar event must occur in both joints. They inferred from this that facet
joints also show an increase in joint space following HVLA (Conway, Herzog, Zhang, Hasler, &
Ladly, 1993; Meal & Scott, 1986)
Cramer et al (2000) were able to provide further evidence for an increase in joint space. By
measuring the increase in joint space following HVLA using MRI, they were able to demonstrate
that the average change in joint separation for the manipulation group was +1.2mm compared to
the average change in the control group of 0.3mm (Cramer, Tuck, Krudsen, & Fonda,
2000).These results are consistent with the hypothesis that spinal manipulation cause a
biomechanical separation of the facet joints within hypomobile joints (Potter, et al., 2005)
B) Hypoalgesia:
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Biomechanical changes caused by the manipulation are thought to have physiological
consequences by means of their effects on the inflow of sensory information to the central
nervous system. By releasing trapped meniscoids, discal material or segmental adhesions, the
mechanical input may ultimately reduce noiciceptive input from receptive nerve endings in
innervated paraspinal tissues. (Picker, 2002)
Similarly Bogduk & Jull (1985) identified that fibro-adipose meniscoids are structures capable of
creating a painful situation and therefore reviewed the possible role of fibro-adipose meniscoids
causing pain. They proposed that a HVLA manipulation, involving gapping of the
zygoapophyseal joint, reduces the impaction and opens the joint, encouraging the mensicoid to
return to its normal anatomical position in the joint cavity. This ceases the distension of the joint
capsule, thus reducing pain. (Bogduk & Jull, 1985)
Physiologically, spinal manipulation therapy is purported to relieve pain through modulation of
noiciceptive input through a barrage of afferent input to the central nervous system resulting in
pain reduction and improved perceived function for up to 6 months (Learman et al., 2009).
A study by Cecchi et al compared short- and long-term effects of three treatments for chronic,
non-specific low back pain: spinal manipulation, individual physiotherapy treatments and back
school (group back exercises with patient information/education and ergonomic training aimed at
optimizing functional recovery. Results showed that pain scores at one year after intervention
remained significantly lower than baseline scores for the back school and spinal manipulation. In
chronic non-specific low back pain, spinal manipulation provided more functional improvement
and pain relief, and reduced drug intake than individual physiotherapy programs and back
school. (Cecchi, Molino-Lova, Chiti, & Pasquini, 2010)
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The current study is the first to report that SMT specifically inhibits temporal summation in
individuals with LBP. Additionally, this inhibition appears local, as it was observed only in the
lower extremity and psychological factors were not strongly associated with resultant inhibition
of temporal summation. These findings suggest that inhibition of temporal summation is a
potential mechanism for pain relief following SMT for individuals with LBP (Bialosky, Bishop,
Robinson, & Zeppieri, 2009).
It has also been demonstrated that zygapophyseal HVLA manipulation causes not only a
reduction of paraspinal hyperalgesia in subjects with symptoms, but also an increase in
paraspinal pain thresholds to a noxious stimulation in subjects with no symptoms Therefore it
seems more appropriate to describe one of the neurophysiologic effects of zygapophyseal HVLA
manipulation as creating hypoalgesia (Evans, 2002). As a result, a link therefore could be
postulated between the long term pain relief from spinal manipulation and the increase in
paraspinal pain threshold creating hypoalgesia.
C) Other neurophysiological effects
HVLA has been reported to cause numerous neurophysiologic effects at both the spinal cord and
cortical levels. One of the proposed central effects is called facilitation or sensitization. This
refers to the increased excitability or responsiveness of dorsal horn neurons to an afferent input.
An alteration between vertebral segments may produce a biomechanical overload leading to the
alteration of signalling from mechanically or chemically sensitive neurons in paraspinal tissues.
These changes in afferent input are believed to alter neural integration either by directly affecting
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reflex activity and/or by affecting central neural integration within motor and neuronal pools
[Pickar].
Denslow et al were one of the first groups to investigate this phenomenon, and their findings
suggested that motoneurons could be held in a facilitated state because of sensory bombardment
from segmentally related dysfunctional musculature. It has been shown that central facilitation
increases the receptive field of central neurons and allows innocuous mechanical stimuli access
to central pain pathways [Woolf]. Essentially this means that sub-threshold stimuli may become
painful as a result of increased central sensitization. As discussed in the other sections of this
proposal, spinal manipulation is believed to be able to overcome this facilitation by making
biomechanical changes to the joint [Pickar], and/or by creating a barrage of afferent inputs into
the spinal cord from muscle spindle and small-diameter afferents, ultimately silencing
motoneurons. [Korr].
Melzack and Wall’s [#] Gate Control Theory describes the dorsal horn of the spinal cord as
having a gate-like mechanism which not only relays sensory messages but also modulates them.
Noiciceptive afferents from small diameter Aγ and C fibres tend to open this gate, and nonnoiciceptive large diameter Aβ fibres (from joint capsule mechanoreceptor, secondary muscle
spindle afferents, and coetaneous mechanoreceptors) tend to close the gate to the central
transmission of pain. This modulation takes place in the lamina of the dorsal horn. Simplistically,
Aβ afferents enter lamina II and V, stimulating an inhibitory interneuron in lamina II (which
connects to lamina V); Aγ and C fibres enter lamina V. Consequently, the central transmission of
pain is a balance between the influences of these opposing stimuli. [Potter, Kandel] HVLAT may
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modulate the pain gate mechanism in the dorsal horn by producing a barrage of non-noiciceptive
input from large diameter myelinated Aβ afferents from muscle spindles and facet joint
mechanoreceptors to inhibit noiciceptive C fibres [Besson & Chaouch].
Dishman et al recently published an article which questioned some of their own previous
research findings. In this subsequent paper, the authors stated that the H-reflex technique is
susceptible to the effects of pre-synaptic inhibition of the afferent arm of the reflex pathway. So,
by using transcranial magnetic stimulation to directly measure the effect of corticospinal inputs
on the alpha motor neuron pool, they were able to perform an experiment which showed a
transient (20–60 s) increase in motor alpha neuron excitability post manipulation. This paper
lends further support to the theory that spinal manipulation produces a brief activation of the
motor alpha neuron leading to brief muscle contraction.
Descending pathways also influence pain perception. Stimulation of the Periaqueductal gray
produces analgesia via the descending PAG pathways[Morgan MM]. Stimulation of the dorsal
PAG (dPAG) in the brain produces selective analgesia to mechano-nociception, whereas
temperature nociception is modulated via the ventral PAG (vPAG). It is also known that
sympatho-excitation results from stimulation of the dPAG, in contrast to sympatho-inhibition
which occurs as a result of stimulating vPAG[Morgan MM]. Activation of the descending dPAG
is a possible mechanism for the antinociceptive effects of spinal manipulation. Sterling et al
measured changes in pain and sympathetic outflow by comparing a C5/6 HVLA to a sham
intervention (manual contact but with no movement). The authors demonstrated HVLA produced
mechanical hypoalgesia, measured by an increase in pain pressure threshold, and increased
sympathetic outflow, measured by decreased blood flow, decreased skin temperature, and
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increased skin conductance. However, there was no alteration to thermal pain thresholds. Given
such selective mechanical anti-nociception and sympathoexcitation, this supports the theory that
the mechanism of effect is due to activation of the dPAG descending pain mechanism.
Vincenzino et al conducted a similar experiment on subjects with epicondylitis and showed
again that cervical spine HVLA lead to selective analgesia to mechanical stimulus and
sympatho-excitation, adding further weight to the argument that spinal manipulation may
influence the perception of pain by activation of the descending dPAG. This does not prove
conclusively that there is definitely direct activation of dPAG, only that the effects of HVLA are
give similar findings to what you would expect with stimulation of the dPAG, hence there is a
plausible link between the two, and it is inferred that HVLA may lead to stimulation of the
dPAG.
2.4 Motor Evoked Potentials:
The term ‘motor evoked potentials’ (MEPs) is used to describe potentials obtained from muscles
by the stimulation of motor structures in the central nervous system (Chiappa, 1997). These
potentials can be caused by stimulation along any of the motor pathways, but the cerebral cortex
and the cervical spinal cord are the most commonly stimulated areas. Direct electrical activation
of the motor pathways using the cerebral cortex has been used in clinical experiments for many
years. A study in 1980 by P. A. Merton and H. B. Morton used transcranial electrical stimulation
(TES) to cause non-invasive stimulation of MEPs. This method was further refined in 1985 by
Barker et al., with the introduction of transcranial magnetic stimulation (TMS). Although
peripheral muscles and nerves were first investigated with TMS, studies nowadays often focus
on stimulation of the cortex.
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TMS has been found to be a very effective method to measure MEPs. As stated by Dishman
(2008) “…TMS allows for the recording of MEPs from virtually any muscle.” When using TMS
to measure MEPs, there is electrical activation over the region being stimulated via an anode and
a cathode at a distal site measuring the MEP response. When stimulating an area of cortex,
different neural components of the precentral gyrus may become stimulated – the dendrites, the
cell bodies or the axon hillocks. MEP generation depends on the activation of the axon hillocks.
With magnetic stimulation,” an intense current in and external coil induces local depolarising
electrical currents that flow through the neuron and axon hillock” (Daube, 2002). It is this
depolarisation that initiates descending action potentials in the corticospinal pathways and cause
an MEP to be produced.
The size of the MEP obtained from muscle stimulation is a measure of the size or effectiveness
of the corticospinal output caused by the stimulus, and also the excitability of the neurons in that
pathway (MacDonell et al., 1991). An MEP reading consists of an initial D (direct) wave is
followed by several I (indirect) waves, which come at periodic intervals (usually about 1
millisecond) or ‘latency period’, being the time between the MEP waves and the stimulation. Dwaves represent the “direct excitation of corticospinal tract neurons” (Jasvinder, 2009), while Iwaves reflect “indirect depolarization of the same axons via corticocortical connections”
(Jasvinder, 2009). Larger MEPs may be produced with increased excitability of cortical and
spinal neurons due to not only direct stimulation of these structures, but also stimulation of
surrounding neurons (Capaday and Stein 1987; Butler et al, 1993). Motor neurons that contribute
directly to the muscle activation may be unresponsive at the time of stimulation, but as found by
Darling, et al.,(2006) “…for low level contractions one would only expect only a small
percentage would be in this state because force is maintained by asynchronous activation of a
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number of motor units.”
MEPs in muscles may be elicited by TMS with or without voluntary contraction of the muscle.
However, as found by Rothwell et al.,(1991), Maertens de Noordhout et al., (1992), and
Hauptman and Hummelsheim (1996), “voluntary preactivation is known to increase the
magnitude of motor evoked potentials”. Although with increasing exercise levels the amplitude
of MEPs decreases. This was found by Joaquinn, et al., (1993), where a “transient decrease in the
amplitude of MEPs to TMS following a period of repetitive muscle activation to the point of
subjective fatigue in healthy humans”. The findings from this study were supported by
Giampietro, et al., (1995), in that decreases in MEP amplitude following repetitive exercises may
indicate a level of central nervous system neurophysiological fatigue. The results from both of
these studies also support the theory of this postexercise exhaustion to be due to a depletion of
the acetylcholine that is immediately available.
The major values of obtaining MEPs and carrying out MEP studies have been in measuring
nervous system pathways inoperatively, and also clinically in conditions of the nervous system
such as multiple sclerosis, where slowing of impulse conductions can be measured and
monitored. In the case of this study the measuring of MEPs will help determine the effectiveness
of a particular manual therapy technique, and what effects it does have at a neurophysiological
level.
2.5 Summary:
Spinal manipulation or high velocity, low amplitude (HVLA) techniques are widely used by
manual therapists. This technique has been demonstrated to produce local and general analgesic
effects, and may produce these effects through physiological mechanisms (stretching joint
capsules, resetting neural pathways, etc.) as well as non-specific mechanisms, such as a
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psychological placebo effect. Osteopaths believe that the application of HVLA to dysfunctional
areas of the body can reduce TART findings (tissue texture change, asymmetry, decreases in
ranges of motion and tenderness), reduce pain levels and have effects more distal to the
application site. Given that the lumbosacral level of the spinal cord provides innervations to the
gastrocnemius muscle, manipulation of lumbosacral joints may help reduce signs of dysfunction
in segmentally related tissues.
Previous studies have examined the effects of HVLA at a neurophysiological level. One of the
proposed theories of the mechanism of HVLA is facilitation or sensitisation, meaning that by the
technique causes an increase in the excitability or responsiveness of the dorsal horn in the spinal
cord, resulting in changes in reflex activity and/or central integration. Other studies have found
that manipulation can cause mechanical hypoalgesia, resulting in increases in the pain pressure
threshold and increased sympathetic outflow.
These studies have looked at various muscular outputs including the H-reflex and muscle evoked
potentials (MEPs) from HVLA techniques. The H-reflex is the electrically induced version of the
spinal stretch reflex (monosynaptic), whilst MEPs are produced by stimulating higher order
regions (the cerebral cortex) to produce depolarisation of descending motor pathways and an
MEP to be elicited from a certain muscle. In 1985 a study by Barker et al., pioneered the use of
transcranial magnetic stimulation (TMS), a non-invasive technique which used stimulation of the
cortex to elicit action potentials through the axon hillocks of specific neurons in specific neural
pathways. Since then TMS has been found to be a very effective means of stimulating MEPs,
clinically aiding in measuring nervous system pathways inoperatively.
Lumbosacral manipulation & MEP
25
In this study, TMS will be used to stimulate the descending motor pathways to the lower limb,
namely to the gastrocnemuis muscle, and MEPs recorded. An MEP consists of 2 parts, an initial
direct wave followed by several indirect waves. MEPs have been found to be elicited by TMS
with or without voluntary contraction of that muscle; however voluntary preactivation has been
found to increase the magnitude of the waves produced. The aim of this study is to determine
whether high velocity, low amplitude (HVLA) techniques can alter the corticospinal excitability
on the motorneurons innervating the gastrocnemius muscle using transcranial magnetic
stimulation (TMS), as suggested by a previous study (ref Dishman). This study will build on the
findings of previous studies and may clarify the neurological changes that occur following
HVLA manipulation. Our study focuses on applying the technique to the Lumbo-Sacral junction
to facillitate changes in the lower limbs, specifically the gastrocnemius muscle.
Lumbosacral manipulation & MEP
26
3. AIMS
The aim of this study is to determine whether high velocity, low amplitude (HVLA) techniques
can alter the corticospinal excitability of the motorneurons innervating the gastrocnemius muscle
using transcranial magnetic stimulation (TMS). Previous studies have investigated the effects of
HVLA using TMS in the paraspinal muscles and the gastrocnemuis muscles, finding that HVLA
has a transient increase in central motor excitability. This study aims to build on the results from
these studies and to further investigate the effects of HVLA techniques at a neurophysiological
level
Lumbosacral manipulation & MEP
27
4. METHODS
4.1 Participants:
Participants for this study will be drawn from the student population at Victoria
University. Volunteers will be recruited via posters placed around the teaching clinics and
university campuses at both the City Flinders and Footscray Park Campus. Volunteers will be
invited to contact the principal researcher to indicate their interest to participate in the study and
discuss what will be required of them. These volunteers will be sent Information to Participants
sheets and will sign Consent forms if willing to participate.
Based on an estimate of a large pre-post effect size (d = 0.97) in the only similar study
(Dishman 2002) and analysis with ANOVA, 21 healthy participants will provide the study with
80% power.
A) Inclusion criteria
Healthy participants of either gender without current low back pain, aged between 18 and
50 years old.
B) Exclusion criteria
Participants will be excluded from this study if they are currently suffering from lower
back pain. A neurological screening examination will be performed by one of the researchers to
exclude subjects with radiculopathy or peripheral neuropathy. Participants will also be excluded
if they exhibit any history signs that are contraindicative to HVLA..
4.2 Experimental design:
Lumbosacral manipulation & MEP
28
The study will be a controlled cross-over design where participants will be undergo both
the control and experimental intervention, tested one week apart. The order of the treatment
intervention will be randomised.
4.3 Procedure:
A) Measurement of MEP
Participants will be seated and a snugly fitting cap, with premarked sites at 1 cm spacing,
will be placed over the participant’s head and positioned with reference to the nasion-inion and
interaural lines. Sites near the estimated motor centre of the gastrocnemius muscle (2 - 4 cm
anterior to the interaural line) will be first explored to determine the site at which the largest
motor-evoked potential (MEP) can be obtained. Transcranial magnetic stimulation (TMS) will
be delivered using a Magstim 2002 stimulator (Whitland, UK) with a 5 cm diameter, figure-ofeight coil which will be held tangential to the skull in an antero-posterior orientation. The
coordinates on the cap will be recorded and this site will be used for further measurements.
After determining the optimal stimulation site and individual motor threshold (defined as the
lowest stimulation to evoke an MEP above 50 μV in 50% of MEPs), 10 MEP's (spaced 4 - 5 s
apart) will be recorded at 20% above motor threshold as baseline values. Participants will then
relocate to a treatment table and an intervention will be randomly allocated and performed.
Immediately after the intervention, MEP's will be measured at 20 s intervals within the first 120 s
to determine the acute time course of post manipulation effects on central motor pathways.
MEP's will also recorded at 5 and 10 minutes after manipulation. Participants will return for a
second session one week later and will receive the same procedures with the alternative
intervention.
Lumbosacral manipulation & MEP
29
B) Interventions
i.
HVLA
A right sided L5-S1 side-posture HVLA manipulation will be administered. The patient
is placed in a side-lying position, with hips in approximately 20 degrees of flexion. The lower
left leg is left straight, with the upper right leg slightly flexed. The upper body is rotated to the
right until the level of L5-S1. The clinician then manually contacts the tissues overlying the
zygapophyseal joint, reinforcing both the lower and upper body rotation. Ensuring that the
participant is relaxed and once tissue tension was maximised, a HVLA force is applied. The
thrust is applied in the direction of the apophysial joint plane, commonly in a direction of a line
along the long axis of the patient's right femur (Gibbons & Tehan, 2008).
ii.
Control group:
The operator will assist the participant into a side posture; however no truncal torque will
be applied and no manual contact will be made with the spine.
4.4 Statistical Analysis:
Data will be collated using Microsoft Excel and analysed using SPSS version 18.
Analysis of within and between group changes in MEP from baseline, immediately after
intervention and 5 minutes after intervention will be performed using a split plot ANOVA
(SPANOVA). Cohen’s d effect sizes will also be calculated on the pre-post data. The alpha level
will be set at 0.05
Lumbosacral manipulation & MEP
30
5. ETHICS
Before the study is conducted, an ethics document will be submitted to the Victorian University
Human Research Ethics Committee.
All participants in our study will be voluntarily participating and are free to withdraw at any
stage. Similarly all personal information gathered from the patient will remain confidential and
will only be viewed by researchers conducting the study.
Possible ethical issues that could arise from our study are:

Adverse effects to HVLA such as local pain and discomfort, headache, tiredness or
fatigue, radiating pain or discomfort, parasthesia, dizziness, nausea, stiffness, hot skin or
fainting (Gibbons & Tehan, 2006)

Distress associated with manual therapy such as being undressed in front of researchers
and having their hands placed on them whilst they perform the HVLA

Psychological impact of the TMS procedure

Side-effects from TMS

Method of recruitment- whether it is coercive, and whether the patients will benefit from
being in the study
Ways we can minimize potential risks are:

Patients will be neurologically screened before participating in the study, to rule out
possible contraindications to HVLA

All patients will have a private area to disrobe and appropriate gowns will be given for
participants to wear. Towels will also be used to drape the patient adequately

Patients will be given a consent form to sign

Patients will have the right to withdraw from the study at any time
Lumbosacral manipulation & MEP

A qualified and experienced practitioner will be performing the HVLA and a practitioner
with a doctorate in TMS will be administering and using the equipment
How adverse events will be managed if they occur:

A qualified first aid practitioner will be present

A qualified Osteopathic practitioner able to assess and manage adverse reactions to
HVLA will be present

31
A qualified psychologist will be available for counselling after the study
Lumbosacral manipulation & MEP
6. TIMELINE
Proposal
Mar-10
Apr-10
May-10
Jun-10
Jul-10
Aug-10
Sep-10
Oct-10
Nov-10
Dec-10
Jan-11
Feb-11
Mar-11
Apr-11
May-11
Jun-11
Jul-11
Aug-11
Sept-11
Ethics
Testing
Data Analysis
Write up
32
Lumbosacral manipulation & MEP
6. BUDGET
No budget will be required for this project.
33
Lumbosacral manipulation & MEP
34
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