ON Chiropractic
of C-Sens, clinicians and researchers
can use them as an easy-to-identify
clinical indicator of sensitization and its
resolution.
Spinal Manipulative Therapy
A
2013 validated sham-controlled
trial investigated the ability of
spinal manipulative therapy (SMT)
to relieve pain in myofascial trigger points
within and across spinal segments. They
did this by monitoring trigger points in
the infraspinatus (C5) and gluteus medius
(not C5) muscles, as in the previous
capsaicin study. By performing real and
“sham” SMT manipulations at C5-C6,
they could measure the effect of SMT
and whether this effect was observed
within the local segment or extended
beyond it.
Two chiropractors were required for
the study. “Clinician A” was the “treating”
clinician, responsible for conducting
the history and physical assessment
of participants and performing SMT.
“Clinician B” was the “assessing” clinician,
responsible for identifying trigger points
and measuring pain pressure threshold
values. This study was blinded so
that Clinician B was not aware which
participants received real or sham SMT.
Each participant lay face down while
Clinician B identified trigger points in
the right infraspinatus and right gluteus
medius muscles. These trigger points
were marked on the skin and Clinician
B recorded pain pressure threshold
readings by applying increasing force on
each trigger point until the participant
reported a dull, achy discomfort or
referred pain. Clinician B then left the
room, and Clinician A entered.
Each participant now lay face up
with their head resting on a mechanical
drop headpiece, ready to receive
SMT from Clinician A. Those in the
manipulation group received a bilateral
rotary manipulation targeting the C5-C6
segment. Those in the control group
received a validated manual sham
manipulation procedure which feels like
a real manipulation but which does not
achieve intersegmental manipulation at
any cervical segment.
Clinician A then left the room and
SMT and Gate Control
T
he gate control theory proposes
that a “gate” in the dorsal horn
of the spinal cord can allow or
prevent pain input to be transmitted to
the brain. Two kinds of fibers control
this gate: large fibers which carry touch,
pressure, vibration and proprioception
“There must be a common mechanism that
is linking all of these conditions,” Dr. Srbely
says. “When I started digging deeper into
this, my hypothesis began to emerge: central
sensitization.”
Dr. John Srbely
Clinician B returned to record pain
pressure threshold values again at 1, 5,
10 and 15 minutes after the manipulation
procedure while the patient rested on
the treatment table.
This study found that patients
who received real SMT had statistically
significant decreases in pressure pain
sensitivity in the infraspinatus muscle
at 1, 5, 10 and 15 minutes. Participants
who received sham SMT experienced
no relief, and neither set of participants
experienced significant changes in the
gluteus medius.
These observations suggest that SMT
can decrease the pressure sensitivity of
myofascial trigger points within a spinal
segment. One mechanism proposed
by the authors is that SMT may mitigate
central sensitization by bombarding the
spinal cord with mechanostimulation,
using the gate control mechanism to
raise the pain threshold.
sensations, and small fibers which carry
temperature and pain sensations. When
the gate receives more stimulus from the
small fibers than the large fibers, it opens
to allow pain signals through. When it
receives more stimulus from the large
fibers, it closes.
This opens two pain relief options:
(1) reduce pain input from the small
fibers, or (2) increase input from the
large fibers. SMT floods the gate with
large-fiber stimulus (touch and pressure),
closing the gate. In order to overcome
the large-fiber stimulus, pain input needs
to increase. This theory explains the
relationship between SMT and higher
pain thresholds in trigger points observed
in this study. Pain input could only get
through if it was more intense than the
large-fiber stimulation of SMT.
Activity from descending fibers in
supraspinal regions could also close
the gate from above. “Based on this
rationale,” Dr. Srbely writes in the SMT
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