ABSTRACT
Background
Dry needling treatment focuses on restoring normal muscle function in patients with musculoskeletal pain; however, little research has investigated this assertion. Shear wave elastography (SWE) allows quantification of individual muscle function by estimating both resting and contracted muscle stiffness.
Objective
To compare the effects of dry needling to sham dry needling on lumbar muscle stiffness in individuals with low back pain (LBP) using SWE.
Methods
Sixty participants with LBP were randomly allocated to receive one session of dry needling or sham dry needling treatment to the lumbar multifidus and erector spinae muscles on the most painful side and spinal level. Stiffness (shear modulus) of the lumbar multifidus and erector spinae muscles was assessed using SWE at rest and during submaximal contraction before treatment, immediately after treatment, and 1 week later. Treatment effects were estimated using linear mixed models.
Results
After 1 week, resting erector spinae muscle stiffness was lower in individuals who received dry needling than those that received sham dry needling. All other between-groups differences in muscle stiffness were similar, but non-significant.
Conclusion
Dry needling appears to reduce resting erector spinae muscle following treatment of patients with LBP. Therefore, providers should consider the use of dry needling when patients exhibit aberrant stiffness of the lumbar muscles.
KEYWORDS: Dry needling, ultrasound, elastography, muscle, low back pain
1. Introduction
Dry needling is performed by inserting needles into painful areas of muscle that are perceived to have motor abnormalities in an attempt to restore normal muscle function and relieve pain [1,2]. A growing body of research supports the clinical effectiveness of dry needling for a variety of neuromusculoskeletal conditions including low back pain (LBP) [3–10]. However, specific evidence of physiologic effect, to include the effect on muscle function, is more limited [11]. Normal muscle function includes both the absence of muscle activation during rest and appropriate amount of muscle activation during contraction. Alternatively, impaired muscle function can include abnormal muscle activation during rest and diminished muscle activation during contraction [12].
Multiple dry needling studies have included muscle function as a secondary outcome for a variety of neuromusculoskeletal conditions. Most studies used some sort of dynamometry to measure contracted muscle function and reported no effect of dry needling on muscle force [13]. Two of the studies used ultrasound imaging to evaluate changes in muscle function after dry needling and reported improved ability to contract the lumbar multifidus muscle after dry needling [14,15]. Another study used electromyography (EMG) to measure lumbar multifidus muscle function in patients with LBP and found no post-needling changes in muscle activation [16].
Ultrasound shear-wave elastography (SWE) is an emerging technology that quantifies stiffness or elasticity of soft tissue by measuring the propagation speed of ultrasound-induced shear-waves within the tissue. Since muscles consistently get stiffer when contracted, SWE has recently been advocated as being the best method of estimating individual muscle function and muscle stiffness can be used as a surrogate measure of muscle activation and muscle force [17]. The single study to date that used SWE to measure changes after dry needling included a small sample (n = 7) of patients with palpable trigger points in their upper trapezius muscle and reported a significant reduction of resting stiffness after dry needling [18]. No study to date has used SWE to evaluate muscular changes after dry needling in patients with LBP or included a large sample of patients.
The primary purpose of this study was to compare the effects of dry needling and sham dry needling, on lumbar muscle stiffness in individuals with LBP using SWE. We also compared the effects of dry needling and sham dry needling on self-reported pain, disability, overall self-perceived changes, and lumbopelvic range of motion (RoM). We hypothesized that dry needling would decrease resting stiffness in the paraspinal musculature and increase stiffness during voluntary contraction of the lumbar multifidus when compared to the sham dry needling. Additionally, we expected that dry needling would improve self-reported clinical outcomes and lumbopelvic RoM to a greater extent than sham dry needling.
2. Methods
2.1. Study design
This study was a parallel arm randomized control trial and was registered at ClinicalTrials.gov (NCT02352532). The primary outcome was muscle stiffness which was assessed as shear modulus using SWE. Secondary outcomes were self-reported pain (assessed with numeric pain rating scale – NPRS), LBP-related disability (assessed with the Oswestry Disability Index – ODI), self-reported overall change (assessed with the Global Rating of Change – GRoC), and lumbopelvic RoM (flexion, extension, and side-bending). Muscle stiffness was assessed at baseline, immediately after treatment, and approximately one week (5–7 days) after treatment. Self-reported clinical outcomes and RoM were assessed at baseline and approximately one week later.
2.2. Participants
Participants with current LBP were recruited via advertisements from the San Antonio Military Healthcare System between June 2015 and March 2017. Current LBP was defined as pain between the 12th rib and buttocks causing at least a minimally important level of physical disability (operationally defined as having an ODI score of at least 10%) [19]. To participate, volunteers were also required to be a Department of Defense healthcare beneficiary (active duty military or civilian dependent) and be between 18 and 65 years of age. Individuals were excluded from participation if they reported being pregnant, having a history of surgery to the lumbosacral spine, or receiving manual therapy, acupuncture, or dry needling interventions to the lumbosacral spine within the previous 4 weeks. Volunteers who exhibited signs of lumbar radiculopathy or non-musculoskeletal pathology (e.g. cancer, cauda equina syndrome, infection) were also excluded. The study protocol was approved by the Institutional Review Board of Brooke Army Medical Center (approval # C.2015.020d) and the rights of the participants were protected.
2.3. History and physical examination
After providing informed consent, medical history and demographic information was collected via self-report to include prior history of LBP, duration and location of current symptoms, prior surgeries and treatments, age, sex, height, and weight. Participants then underwent a standardized clinical examination that was administered by a trained examiner. This examination included a brief clinical history, self-reported pain, disability, fear avoidance behavior (as measured by the Fear Avoidance Behavior Questionnaire), and a physical examination. The most symptomatic side (right or left) at the most symptomatic level (L3, L4, or L5) was identified by the examiner based on a combination of viewing the patient self-reported pain diagram and tenderness during the palpatory examination. The palpatory exam included manual pressure on each lumbar spinous and transverse processes at levels L3, L4, and L5 in a posterior to anterior direction [20].
2.4. Shear wave elastography imaging
All SWE images were obtained using a Supersonic Aixplorer ultrasound system (Supersonic Imagine, Aix-en-Provence, France) with a 50 mm 10–2 MHz linear transducer. Examiners trained on all imaging-related procedures and practiced on colleagues until an acceptable level of reliability (ICC3,3 > .70) was obtained on 10 individuals before starting data collection. Since impaired contraction of the lumbar multifidus has been previously reported in patients with LBP [21,22], the lumbar multifidus was imaged both at rest and during submaximal contraction. The lumbar erector spinae (iliocostalis and longissimus muscles) were imaged at rest only. Imaging of both muscles was performed only on the most symptomatic side at the most symptomatic level for each participant. If the most symptomatic side and/or level could not be determined, imaging was performed on the right side at the L4 spinous level.
To ensure consistency and maximal rest between contractile conditions, the order of imaging for each participant was (1) erector spinae at rest, (2) lumbar multifidus at rest, (3) lumbar multifidus during contraction. This imaging sequence was completed three times and the average value for each condition was used for analyses, which has demonstrated acceptable reliability in asymptomatic participants [23]. To image the erector spinae muscles, the transducer was placed on the most prominent portion of the musculature immediately above the iliac crest, centered on the selected spinal level. The transducer was oriented in the sagittal plane so it was parallel to the muscle fibers [24], and then angled slightly medially to optimize image clarity (Figure 1). The SWE box overlaying the B-mode ultrasound image was then positioned so it covered the largest region of muscle possible while achieving complete fill and avoiding fascial planes (Figure 2).
Figure 1.
The erector spinae muscle bulk, the iliac crest, and targeted level (e.g. L4 in photo) spinous process were all marked on the must symptomatic side prior to imaging. (Top) To image the erector spinae muscles, the transducer was centered on the paraspinal muscle bulk with the transducer oriented parallel to the spine. (Bottom) To image the lumbar multifidus, the transducer was rotated approximately 20º and tilted approximately 10º medially toward the targeted level facet joint.
Figure 2.
The shear wave elastography (SWE) box, which overlays the B-mode ultrasound image, gives a visual color-coded image based on regional tissue stiffness (Young’s modulus) within the box. Young’s modulus was later converted to shear modulus (kilopascals- kPa).
To image the lumbar multifidus muscles, the transducer was moved slightly medially from the location used for the erector spinae, rotated approximately 20º away from midline, and tilted approximately 10º medially toward the targeted level facet joint (Figure 1). The depth of the image was adjusted for each participant so that both the superficial fascia and facet joint were visible during resting and contracted states. The SWE box was then positioned over the lumbar multifidus muscles, just superficial to the facet joint in order to target the deepest fibers of the lumbar multifidus (Figure 2). After imaging at rest, participants were then instructed to lift their contralateral arm approximately 5 centimeters off the plinth while holding a small weight normalized to approximately 1% of the participant’s body weight and reimaged during contraction. Additional details of these imaging procedures have been reported elsewhere [25,26].
Image analysis was performed offline on a separate computer with device-installed software. A circular Q-Box was sized as large as possible (approximately 15 mm diameter) within the SWE image while ensuring avoidance of any fascial planes, bony prominences, and areas where the Aixplorer Multiwave failed to determine the propagation speed. The Aixplorer Multiwave provides the spatial-mean Young’s modulus value in kilopascals based on the assumed isotropic nature of soft tissues. Since skeletal muscle is unlikely to be isotropic, we calculated shear modulus by dividing the Young’s modulus by three [27].
2.5. Self-report measures and lumbopelvic range of motion
An 11-point Numeric Pain Rating Scale (NPRS) was used to quantify participants’ current back pain intensity between 0 and 10. The NPRS is reliable and responsive (minimally important difference = 2 points) in patients with LBP [28,29]. Self-reported LBP-related disability was quantified with the ODI. The ODI consists of scores ranging from 0 to 100 (with higher scores representing higher levels of disability) and has been found to be both reliable and responsive to change (minimally important difference = 10%) in patients with LBP [19]. Subjective perception of overall change was assessed using the GRoC with a 15-point Likert type scale ranging from −7 (a very great deal worse) to +7 (a very great deal better). The GRoC has been shown to be highly reliable in patients with LBP, and at least moderately responsive (minimally important difference = 2.5 points) [30]. Active lumbosacral RoM of flexion, extension, and side bending was measured using a standard inclinometer centered on the spinous process of the 12th thoracic vertebra. A single measurement was taken for each motion as prior studies have shown adequate reliability of single measures of lumbosacral RoM in patients with LBP [31].
2.6. Randomization
Following the baseline evaluation and outcome assessment, participants were randomized to receive dry needling or sham dry needling. Randomization was performed by a computer-generated randomization list with randomly varying block sizes of 2 and 4 prepared prior to study initiation. Allocation was concealed via opaque envelopes in order to blind all outcome assessors to group assignment and was only revealed to the treating provider immediately before treatment.
2.7. Dry needling and sham dry needling
Treatment was performed by an experienced physical therapist trained in dry needling and blinded to all outcomes. The treating therapist was told by the baseline examiner which side and spinal level were most painful and then performed palpation to further localize the area for treatment to the most painful regions. Treatment was applied to a total of four sites on the most symptomatic side, to both the lumbar multifidi and erector spinae muscles, at the two most symptomatic levels (between L3, L4, and L5). If the therapist was unable to determine the most symptomatic levels or areas, treatment was performed to the middle of the muscle belly at the L4 and L5 levels.
Dry needling treatment included insertion of a sterile, disposable, solid filament 0.30 × 50 mm stainless steel Seirin J-Type or Myotech needle into the lumbar musculature. ‘Clean technique’ was used throughout the treatment procedure which included hand washing, clean latex-free exam glove use, and participant skin preparation with an alcohol swab prior to treatment [32]. For the lumbar multifidus muscle, needles were inserted approximately 1.5 cm lateral to the spinous process at each segmental level in a posterior to anterior direction (Figure 3- top). After piercing the skin, the needles were directed into the muscle with a slight inferior-medial angle (approximately 20º) to the depth of the lumbar lamina. For the erector spinae muscles, the needle was inserted just lateral to the paraspinal muscle bulk (approximately 5–10 cm lateral to the spinous process) in a lateral to medial direction toward the spinous process (Figure 3- bottom). Both segments of each muscle were needled once with needle insertion lasting approximately 5–10 seconds. During each insertion a ‘pistoning’ (in and out motion) technique was used in an attempt to elicit a local twitch response [33].
Figure 3.
Dry needling techniques. (Top) For the lumbar multifidus muscle, needles were inserted approximately 1.5 cm lateral to the spinous process at the most symptomatic side and segmental level in a posterior to anterior direction with a slight inferior-medial angle (approximately 2º) to the depth of the lumbar lamina. (Bottom) For the erector spinae muscles, the needle was inserted just lateral to the paraspinal muscle bulk (approximately 5–10 cm lateral to the spinous process) in a lateral to medial direction toward the spinous process.
Sham dry needling was performed in a manner identical to dry needling treatment, with the exception of the use of a Seirin J-Type or Myotech needle with the tip cut off that did not pierce the skin. The needle was placed in the guide tube to mimic insertion and then was rocked and twisted against the skin so as to simulate dry needling treatment without actually piercing the skin.
After treatment was administered, all participants were verbally instructed in the performance of a supine double knee-to-chest maneuver to be held for 5–10 seconds and repeated 6 times in order to alleviate residual soreness as needed. Subjects were instructed not to initiate any new core exercises, but to maintain their normal level of physical activity throughout the next week. In addition to the described outcome measures, participants were asked about adverse events and side effects of treatment based on previously documented findings [34].
2.8. Statistical analysis
A priori power analysis was performed using G*Power 3 [35]. A large effect size was expected based on the only previous work investigating changes in shear modulus after dry needling treatment [18]. Two groups of 30 subjects provided 82% power to detect an effect size of 0.80 while accounting for up to a 10% drop out rate.
All data were analyzed with IBM SPSS Version 26 software (Windows, Armonk, NY: IBM Corp) and STATA version 16.1 software (StataCorp, College Station, Tx). Baseline characteristics for the dry needling and sham dry needling groups were summarized and compared to ensure similar groups. Linear mixed modeling has been advocated for longitudinal data analysis as it is more flexible and does not rely on assumptions of equal variance and correlations among repeated measurements like analysis of variance (ANOVA) procedures [36]. Therefore, treatment effects were estimated using separate, random intercept linear mixed models for each outcome (muscle shear modulus, NRPS, ODI, and lumbopelvic RoM). Time and treatment group were modeled as fixed effects and the baseline outcome score was included as a covariate within each model. The hypothesis of interest was the time-group interaction at each timepoint, which was examined with pairwise comparisons of the estimated marginal means. Since GRoC scores were only obtained 1 week after treatment, they were compared between groups using an independent t-test. Consistent with intention-to-treat analysis, all missing values were imputed using multiple imputation prior to other analyses. Significance for all statistical analyses was set a priori using 2-tailed α = 0.05.
3. Results
Participant recruitment and exclusion flow is outlined in Figure 4. One participant in the dry needling group did not return for the one-week follow-up assessment and did not respond to attempts to reschedule. Descriptive statistics of baseline demographic, clinical history, and examination data are listed in Table 1. Sex and duration of symptoms were somewhat different between the groups and, therefore, were assessed for use as covariates for all analyses. However, since they were not statistically related to any primary or secondary outcome measure they were not included in the mixed models.
Figure 4.
Flow of participant recruitment and exclusion. Abbreviation: SLR, Straight Leg Raise Test; ODI, Oswestry Disability Index.
Table 1.
Baseline characteristics for dry needling and sham dry needling groups.
| Characteristics | ||
|---|---|---|
| Dry Needling (n=30) | Sham Dry Needling (n = 30) | |
| Age (years) | 32.2 (8.2) | 32.3 (6.6) |
| Sex (% women) | 46.7% | 33.3% |
| BMI | 26.2 (3.5) | 26.0 (3.0) |
| ODI | 20.6 (7.6) | 20.1 (6.6) |
| NPRS | 2.0 (1.7) | 1.7 (1.5) |
| Symptom duration (months) | ||
| Mean (SD) | 84.6 (90.7) | 68.7 (73.5) |
| Median (IQR) | 55.0 (11.0–129.0) | 36.5 (7.8–91.5) |
| FABQ-W | 12.3 (5.9) | 13.7 (7.5) |
| FABQ-PA | 12.3 (5.1) | 13.0 (5.4) |
| Previous episodes of back pain (%) | 70.0% | 56.7% |
| Flexion RoM (degrees) | 95.7 (16.1) | 100.3 (18.5) |
| Extension RoM (degrees) | 24.0 (10.9) | 26.1 (12.3) |
| Total side-bending RoM (degrees) | 58.4 (12.9) | 54.7 (14.5) |
| Side-bending asymmetry RoM (degrees) | 5.2 (6.6) | 4.9 (4.7) |
Values are means (SD, standard deviation) unless stated otherwise.
Abbreviations: BMI, body mass index. ODI, Oswestry Disability Index. NPRS, numeric pain rating scale. SD, standard deviation. IQR, interquartile range. FABQ-W, Fear Avoidance Behavior Questionnaire-Work subscale. FABQ-PA, Fear Avoidance Behavior Questionnaire-Physical Activity subscale. RoM, range of motion.
Results of primary outcome analyses of muscle stiffness are detailed in Table 2. Resting erector spinae muscle stiffness was lower in individuals that received dry needling than in those that received sham dry needling 1 week, after treatment after adjusting for baseline differences (p = 0.019). Specifically, resting erector spinae muscle stiffness decreased by a mean of 13.5% in the dry needling group compared to an increase of 6% in the sham dry needling group 1 week after treatment (Figure 5). There were no other statistically significant between-groups differences in any muscle condition at any follow-up timepoint (p = 0.089 to 0.551). However, point estimates of muscle stiffness consistently decreased in individuals that received dry needling and increased or did not change in those that received sham dry needling in all muscle conditions both immediately after treatment and one week later.
Table 2.
Primary outcomes of muscle stiffness (shear modulus in kilopascals- kPa) of the erector spinae and lumbar multifidus muscles before needling (baseline), immediately after needling (post-needle), and at 1-week follow-up. *Denotes statistical significance (p < .05).
| Outcome/Visit | Dry Needling |
Sham Dry Needling |
||||
|---|---|---|---|---|---|---|
| Mean (SD) | Mean Change from Baseline (95%CI) | Mean | Mean Change from Baseline | Adjusted Between-Group Difference (Dry Needling – Sham) | P Value | |
| Erector Spinae Muscle Stiffness (kPa) – Resting | ||||||
| Baseline | 6.4 (3.6) | 6.4 (3.2) | ||||
| Post-needle | 6.2 (3.7) | −0.2 (−0.7, 0.4) | 6.5 (3.4) | 0.1 (−0.4, 0.7) | −0.0 (−1.4, 0.7) | 0.551 |
| 1-week | 5.6 (3.7) | −0.9 (−1.9, 0.1) | 6.8 (3.2) | 0.4 (−0.6, 1.4) | −1.3 (−2.3, −0.2) | 0.019* |
| Lumbar Multifidus Muscle Stiffness (kPa) – Resting | ||||||
| Baseline | 6.2 (2.4) | 7.4 (3.8) | ||||
| Post-needle | 6.0 (1.9) | −0.2 (−1.1, 0.6) | 7.4 (3.0) | 0.0 (−0.8, 0.9) | −0.7 (−2.0, 0.6) | 0.279 |
| 1-week | 5.9 (2.9) | −0.3 (−1.5, 0.9) | 7.4 (4.6) | 0.0 (−1.2, 1.2) | −0.8 (−2.1, 0.6) | 0.254 |
| Lumbar Multifidus Muscle Stiffness (kPa) – Contracted | ||||||
| Baseline | 19.8 (10.5) | 21.7 (11.3) | ||||
| Post-needle | 19.3 (10.4) | −0.6 (−2.9, 1.8) | 23.3 (13.0) | 1.6 (−0.7, 3.9) | −2.3 (−5.7, 1.0) | 0.175 |
| 1-week | 18.2 (10.5) | −1.7 (−4.4, 1.1) | 22.8 (12.7) | 1.1 (−1.7, 3.8) | −2.9 (−6.3, 0.4) | 0.089 |
Figure 5.
Comparisons in shear modulus (in kilopascals- kPa) of the erector spinae muscle between participants that received dry needling and sham dry needling before treatment (baseline), immediately after treatment (post-needle), and at 1-week follow-up. Error bars denote 95% confidence intervals. *Statistically significant difference at 1-week after adjusting for baseline values.
Results of secondary outcome analyses of self-reported clinical improvement (NPRS, ODI, GRoC) and RoM are detailed in Table 3. Individuals that received dry needling reported statistically larger overall improvement (GRoC) (p = 0.016) and exhibited statistically larger change in lumbopelvic flexion RoM (p = 0.008) than did individuals that received sham dry needling 1 week after treatment. There were no other statistically significant between-groups differences in NPRS, ODI, or lumbopelvic extension or side-bending RoM (p = 0.182 to 0.716) 1 week after treatment. Both dry needling and sham dry needling groups reported statistically significant improvements in both pain (NPRS) and LBP-related disability (ODI). However, point estimates were smaller than established minimally important differences indicating changes might not be clinically important.
Table 3.
Secondary outcomes of self-reported clinical improvement and lumbopelvic range of motion 1 week after treatment. *Denotes statistical significance (p < .05).
| Outcome/Visit | Dry Needling |
Sham Dry Needling |
Adjusted Between-Group Difference (Dry Needing – Sham) | P Value | ||
|---|---|---|---|---|---|---|
| Mean at 1-week | Mean Change from Baseline | Mean at 1-week | Mean Change from Baseline | |||
| Self-reported Clinical Improvement | ||||||
| Numeric Pain Rating Scale | 1.2 (1.8) | −0.8 (−1.3, −0.2)* | 1.1 (1.8) | −0.6 (−1.1, −0.0)* | −0.1 (−0.8, 0.6) | 0.716 |
| Oswestry Disability Index | 13.7 (7.2) | −7.0 (−9.7, −4.3)* | 15.4 (7.1) | −4.7 (−7.5, −2.1)* | −1.9 (−5.1, 1.2) | 0.228 |
| Global Rating of Change | 2.2 (2.8) | 2.2 (1.4, 3.0)* | 0.8 (1.5) | 0.8 (−0.01, 1.6) | 1.4 (0.3, 2.6)* | 0.016* |
| Range of Motion | ||||||
| Flexion | 90.3 (22.7) | −5.5 (−11.4, 0.4) | 103.6 (14.4) | 3.3 (−2.6, 9.1) | −10.3 (−17.8, −2.7)* | 0.008* |
| Extension | 26.4 (10.7) | 2.4 (−1.1, 5.9) | 25.7 (9.8) | −0.4 (−3.9, 3.1) | 1.8 (−2.2, 5.9) | 0.373 |
| Total side-bending | 58.0 (13.2) | −0.5 (−4.4, 3.5) | 56.6 (13.9) | 1.9 (−3.5, 4.4) | −1.2 (−6.1, 3.8) | 0.646 |
| Side-bending asymmetry | 3.7 (3.9) | −1.4 (−3.9, 1.0) | 5.1 (4.2) | 0.2 (−2.2, 2.6) | −1.4 (−3.4, 0.6) | 0.182 |
No serious adverse events were reported throughout the course of this study. However, several participants reported mild side effects that had resolved before the 1-week follow-up assessment. Two participants that received dry needling and four participants that received sham dry needling reported pain during treatment. Additionally, two participants that received dry needling reported dizziness and one reported an unspecified emotional change after treatment. Statistically more participants (p = 0.030) in the dry needling group (83%) than in the sham dry needling group (56%) thought that they received true dry needling during treatment.
4. Discussion
The primary purpose of the current study was to compare the effect of dry needling to sham dry needling on lumbar muscle stiffness in individuals with LBP using SWE. We hypothesized that dry needling would decrease resting stiffness in the paraspinal musculature and increase stiffness during voluntary contraction of the lumbar multifidus when compared to the sham dry needling. Additionally, we compared the effect of dry needling and sham dry needling on self-reported pain, disability, overall change, and lumbopelvic RoM. We expected dry needling to improve self-reported clinical improvement measures and lumbopelvic RoM to a greater extent than the sham dry needling.
4.1. Muscle stiffness
In support of our hypothesis, resting erector spinae muscle stiffness was statistically lower in individuals that received dry needling than in those that received sham dry needling after adjusting for baseline differences. However, this was only true 1 week after, and not immediately after treatment and was only significant in the erector spinae and not the lumbar multifidus muscle.
The finding that dry needling appears to reduce resting erector spinae muscle stiffness is consistent with the common application of dry needling to myofascial trigger points which have been defined as hypersensitive taut bands in skeletal muscle [37]. Myofascial trigger points have been have been found to include and spontaneous electrical activity (SEA) [38] and be characterized by localized stiff nodules [39,40]. Limited evidence, at least in animal models, suggests that dry needling into myofascial trigger points can reduce abnormal SEA [38,41]. This reduction of abnormal muscle activity at rest, may allow for more normal coordination of agonist and antagonist muscles and restoration of normal muscle function during routine functional activities [2].
In the single study to date that has used SWE to measure changes in resting muscle function after dry needling, Maher et al. [18] found an immediate reduction of resting upper trapezius muscle stiffness after dry needling in a small sample of patients with palpable trigger points. Our findings regarding resting muscle stiffness are partially consistent with those observed by Maher et al. (2013) as we found a delayed reduction in muscle stiffness 1 week after dry needling, but not immediately after treatment. Additionally, our findings were only statistically significant in the erector spinae and not the lumbar multifidus muscles Figure 5. This muscle-dependent finding is not surprising considering that the erector spinae muscle commonly exhibits excessive contraction in patients with LBP [12], just as the upper trapezius muscle commonly exhibits excessive contraction in patients with neck pain [42].
Contrary to our hypothesis, contracted lumbar multifidus muscle stiffness was not statistically significant different between groups after treatment. Moreover, point estimates of contracted lumbar multifidus muscle stiffness consistently decreased after dry needling and increased after receiving sham dry needling.
The lack of significant change in lumbar multifidus stiffness during contraction is consistent with the majority of studies in other body regions. A systematic review of muscle force during contraction of the shoulder, thigh/knee, ankle, elbow/hand/wrist musculature found no effect of dry needling on muscle force as measured by dynamometry or isometric hold [13]. Additionally, these findings are consistent with a recent study [16] that used EMG to measure contracted lumbar multifidus muscle activation in adults with LBP before and after application of two different dry needling techniques. Using the same contraction strategy and time frames as the current study, Wang-Price et al. [16] found no differences between dry needling techniques and no main effect of time.
Contrary to the findings of the current study, some research has reported variable changes in muscle contraction after dry needling. Nineteen of the 21 studies included in the previously mentioned systematic review demonstrated no effect of dry needling on muscle force [13], however, two studies investigating the effects of dry needling versus simple stretching found dry needling to cause a greater improvement in maximal isometric neck muscle strength that persisted up to six months after intervention [43,44]. Two studies that investigated lumbar paraspinal muscles (as was done in the current study) using ultrasound imaging to measure percent change in muscle thickness found mixed results. Koppenhaver et al. [14], reported larger improvements in lumbar multifidus muscle contraction after dry needling in patients with LBP that responded clinically when compared to those that did not responded clinically one week after treatment. Similarly Dar and Hicks [15], reported a larger improvement in lumbar multifidus muscle contraction after dry needling at one side and spinal level (right L4/5), but not at the other side or spinal levels in asymptomatic individuals.
4.2. Self-reported clinical improvement and range of motion
Both dry needling and sham dry needling groups reported significant improvements in pain (NPRS) and LBP-related disability (ODI) one week after treatment. Although point estimates of improvements in pain and disability both favored dry needling group, the amount of improvement was small and not significantly different between intervention groups. Participants that received dry needling reported statistically larger overall improvement on the GRoC than did those who received sham dry needling. These results regarding clinical outcomes appear to be consistent with systematic reviews of dry needling that report mixed findings that usually, but not always, support the clinical effectiveness of dry needling for a variety of musculoskeletal conditions including LBP [3–10].
Participants that received dry needling exhibited statistically larger change in lumbopelvic flexion RoM, but not extension or side-bending RoM, than did individuals that received sham dry needling one week after treatment. Flexion RoM decreased in participants that received dry needling and slightly increased in those that received sham dry needling. However, point estimates of RoM changes in all directions were very small and likely within measurement error for both groups. Similar studies have reported improved RoM after dry needling in studies in patients with neck pain [45,46], and shoulder pain [47], but not in patients after knee or shoulder surgery [48,49]. To our knowledge, only one case report [50] has evaluated changes in lumbopelvic RoM after dry needling. After treating the lumbar multifidi and gluteal muscles with dry needling, the author observed substantial clinical improvement that was associated with a large increase in lumbopelvic flexion RoM [50].
4.3. Limitations and future research
Various limitations of this study should be acknowledged and may at least partially account for the results providing mixed support for our initial study hypotheses. One potential explanation is large variability observed in stiffness values. Many of the observed standard deviations of muscle shear modulus were larger than 50% of the mean values (Table 2). Such wide variability would decrease the statistical power of our analyses.
Another limitation concerns the chronicity of the study sample. The mean duration of LBP in study participants was 84.6 and 68.7 months (approximately 6–7 years) in the dry needling and sham dry needling groups, respectively. Prior evidence suggests that patients with longer duration of LBP symptoms have a worse clinical prognosis [51], worse outcomes after dry needling treatment [52], and are less likely to exhibit change in lumbopelvic muscle function with treatment [53]. Therefore, the high chronicity of the participants in the current study may have contributed to the small changes in clinical outcomes (pain and disability) after treatment, as well as adversely affected the responsiveness of the paraspinal musculature to a single session of dry needling treatment.
Additionally, it appears that our participant blinding was only partially effective as a greater number of participants in the dry needling group (83%) than in the sham dry needling group (56%) thought that they received true dry needling. Some participants likely had previously received dry needling and/or acupuncture, which could have been a contributing factor. While this is unlikely to affect a physiologic outcome like muscle stiffness, it could have affected the self-report measures such as pain, disability, and overall clinical improvement.
Finally, dry needling is mostly commonly used as a part of a comprehensive multi-model treatment approach that includes the application of other manual therapies and exercise [2]. The fact that dry needling was used in isolation in the current study could have at least partially contributed to the lack of significant differences between those that received sham and true dry needling, especially in self-reported clinical improvement and range of motion.
Future studies should assess for changes in muscle stiffness after dry needling over longer periods of time and when dry needling is combined with other common treatments as is done in the context of clinical care. Future studies should also evaluate for changes in muscle stiffness after dry needling to other muscle groups (e.g. rotator cuff muscles) and in other patient populations (e.g. shoulder pain) and include whether any effect is modified by treating directly into symptomatic trigger points and/or the occurrence of a local twitch response.
5. Conclusions
Dry needling appears to reduce resting erector spinae muscle stiffness following treatment of patients with LBP. Dry needling did not significantly affect lumbar multifidus muscle stiffness in this study, however, point estimates consistently decreased after dry needling and increased or did not change after sham dry needling. Therefore, providers should consider the use of dry needling when patients exhibit aberrant stiffness of the lumbar muscles.
Biography
The authors certify that they have no affiliations with or financial involvement in any organization or entity with a direct financial interest in the subject matter or materials discussed in the article.
This study was approved by the Institutional Review Board of Brooke Army Medical Center
The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Departments of the Army or Defense.
Funding Statement
This work was funded by the Advanced Medical Technology Initiative (AMTI), through the Telemedicine and Advanced Technology Research Center (TATRC) at the U.S. Army Medical Research and Development Command (USAMRDC).
Disclosure statement
No potential conflict of interest was reported by the author(s).
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