Research Design:
This study will be pre-test post-test trial, in which all eligible participants will receive
a single session of dry needling (DN). All outcome measures will be collected before and
immediately after a single session of DN.
Procedure:
Eligible participants will be asked to complete an intake form, asking them about their
demographic data, including age, gender, height, weight, occupation, past medical history,
and questions related to their low back pain (onset, injury mechanism if any, location,
duration, type, and nature). Once the participant's eligibility is confirmed, each
participant will complete the Central Sensitization Inventory (CSI) questionnaire to assign
each participant either in the CS group or non-CS group using the 40 cutoff score of the CSI.
Clinical Assessments:
Each participant will complete 3 self-reported questionnaires before cortical
excitability assessment, including pain intensity determined using the Numeric Pain
Rating Scale (NPRS), disability determined using the Modified Oswestry Low Back Pain
Disability Questionnaire (modified ODI), and quality of life determined by the
Patient-Reported Outcomes Measurement Information System® -short form (PROMIS-29). These
questionnaires will be used to describe the characteristics of the participants in this
study.
Cortical Excitability Assessment:
Three cortical excitability parameters will be collected: amplitudes of motor evoked
potentials (MEPs), intracortical facilitation (ICF) values, and short-interval cortical
inhibition (SICI) values. Participants will lie in a prone position for the
electromyographic (EMG) setup. EMG activity will be collected from the painful side of
the L4-5 area. Following the recommendations of the Surface ElectroMyoGraphy for the
Non-Invasive Assessment of Muscles (SENIAM) project, the electrode for the LM will be
placed at the L4-5 level, approximately 2-3 cm from the midline, and will be aligned
with a line from the posterior superior iliac spine (PSIS) to the interspace between the
L1 and L2 spinous process.
To obtain MEPs of the LM muscle, the M1 (primary motor cortex) will be stimulated while
the participant performs a submaximal voluntary contraction. First, the maximum
voluntary isometric contractions (MVIC) of the LM will be determined. During the MVIC
testing, each participant will perform the maximum upper extremity and trunk lift with
the elbows flexed to approximately 90° and shoulders abducted to approximately 120°, and
maintain the lift for 3 seconds while resisting against a load applied at the opposite
elbow of the painful side by the testing investigator. Two trials each will be performed
and the highest root mean square (RMS) of EMG amplitude will be identified. During the
cortical excitability assessment, a target line representing ~ 20% of highest RMS value
during MVIC will be placed on the real-time EMG monitor while the participant will be
asked to maintain the target LM activation by slightly leaning forward and to maintain
lumbar lordosis in a seated position.
Following the MVIC testing, each participant will be seated on a chair for cortical
excitability assessment. A "hot spot" will be determined while the participant maintains
a 20% submaximal contraction of the LM (i.e., slightly leaning forward and maintain
lumbar lordosis). A hot spot is defined as the site at which the largest MEP amplitude
is obtained at the lowest TMS stimulation intensity or output (0-100%). The double-cone
coil will be positioned over the M1 area opposite to the participant's most painful
side. The intensity of TMS stimulation from one TMS stimulator will begin at 35% of
stimulator output and then will be increased gradually to yield a MEP from the LM until
a 'hot spot' is observed. Next, the active motor threshold (AMT) will be determined. AMT
is defined as the stimulation intensity which yields a peak-to-peak amplitude of MEP
larger than 200 μV in 5 out of 10 consecutive trials. Once the AMT is determined, the
stimulation intensity will be set at 130% of AMT and 10 stimulations will be delivered
to the hot spot. The 10 supra-threshold MEP amplitudes (uV) recorded from the LM will be
averaged and the average will be used for statistical analysis.
For the ICF and SICI testing, two stimuli, one conditioning stimulus and one test
stimulus, will be generated from two TMS stimulators connected by a coil (BiStim Module,
Magstim Co., UK). In ICF, a subthreshold conditioning (second) TMS at the 90% AMT will
be delivered to the hot spot 15 ms after a test (first) TMS at the 100% AMT. In SICI, a
subthreshold conditioning TMS at 70% AMT will be delivered 2 ms before a test TMS at a
supra-threshold test TMS at 120% AMT. For both ICF and SICI, the amplitude of the
conditioned MEP will be expressed relative to the amplitude of the corresponding test
MEP. Ten trials will be performed for each of the ICF and SICI tests, and the average of
the 10 trials will be used for statistical analysis.
Quantitative Sensory Tests (QSTs):
The two QSTs, pressure pain thresholds (PPTs) and conditioned pain modulation (CPM)
tests, will be administered after the cortical excitability assessments both before and
after the DN intervention. During the PPT, participants will be given a response button
to stop testing on their own, and will be instructed to stop the test as soon as the
pressure becomes uncomfortable or painful, and not to allow an uncomfortable or painful
sensation to continue. Four trials will be tested on the most tender point around L4-5,
but the first trial will be counted as a practice trial. The average of the last three
trials will be used for statistical analysis.
For the CPM test, a thermode will be applied to the most tender point of the low back
and then heat temperature will increase at 1°/sec to the point until the participant
perceives the heat stimuli painful at 6/10 on the numeric pain rating scale (NPRS). Two
thermodes which generate heat stimuli at the temperature that the participant rates 6/10
on the NPRS will be used for the CPM testing, one applied to the most tender point of
the low back (test stimulus), and the other on the contralateral side of forearm
(conditioning stimulus). The NPRS scores will be collected under the two conditions:
test stimuli alone and combined test stimuli and conditioning stimuli. The test stimuli
will be applied first for 10 seconds and then the conditioning stimuli for 25 seconds,
so that the second application of the testing stimuli (for 10 seconds) would occur after
15 seconds of conditioning stimuli.
Dry Needling Intervention:
Two lengths of sterile, disposable, 0.30 mm x 60 mm solid filament needles (Seirin
Corp., Shizuoka, Japan) and 0.30 mm x 100 mm solid filament needles (Shanghai Kangnian
Medical Device Co., Ltd., Shanghai, China) will be used in the study. The length of the
needle for each participant will be selected based on the size of the participant. Two
needles will be inserted on or near the most tender point of the low back. Two
additional needles will be inserted on the opposite side at the level of the most tender
point regardless of unilateral or bilateral LBP. After piercing the skin, the needle
will be directed toward the spinous process in a slight inferior-medial angle
(approximately 20-30°). Once the needle is inserted, the treating investigator will use
ultrasound (US) scanner to visualize the needle placement and to confirm that needle has
reached the deeper layer of the LM. Once the needle placement is confirmed, it will be
pulled slightly in and out within the muscle and redirected in small angles for 10
seconds after insertion. The needles will stay (in situ) in the LM for approximately 10
minutes after the insertion and then will be withdrawn.
Statistical Analysis:
Descriptive statistics will be calculated for participant characteristics as well as baseline
outcome measures (amplitudes of MEPs, ICF values, SICI values, PPTs, and CPM scores) of all
participants. Independent t-tests will be used to compare the ratio data of participant
characteristics, self-reported questionnaires, and baseline outcome measures between the two
groups. Chi-square statistics will be used to analyze categorical data of participant
characteristics (e.g., sex, side(s) of pain, testing side).
The statistical analysis used to address the three aims with the alpha level is set at 0.05
for all statistical analyses: 1) three paired-t tests or Wilcoxon signed rank tests for the
three cortical excitability variables (amplitudes of MEPs, ICF values, and SICI values),
respectively, 2) two paired-t tests or Wilcoxon signed rank tests for the two neurosensory
variables (PPT and CPM values), respectively, and 3) three 2 (group) x 2 (time) repeated
measure ANOVAs to compare CS and non-CS group for the 3 cortical excitability variables,
respectively.