Archives of Physical Medicine and Rehabilitation
Volume 90, Issue 8 , Pages 1332-1339, August 2009

Comparison of 3 Needle Sizes for Trigger Point Injection in Myofascial Pain Syndrome of Upper- and Middle-Trapezius Muscle: A Randomized Controlled Trial

  • Seung-Hyun Yoon, MD, PhD

      Affiliations

    • Department of Physical Medicine and Rehabilitation, Ajou University School of Medicine, Suwon, Republic of Korea
    • Corresponding Author InformationReprint requests to Seung-Hyun Yoon, MD, PhD, Dept of Physical Medicine and Rehabilitation, Ajou University School of Medicine, San 5, Wonchon-dong, Yeongtong-gu, Suwon 443-721, Republic of Korea
    • ,
  • Ueon Woo Rah, MD, PhD

      Affiliations

    • Department of Physical Medicine and Rehabilitation, Ajou University School of Medicine, Suwon, Republic of Korea
    • ,
  • Seung Soo Sheen, MD, MS

      Affiliations

    • Section of Clinical Epidemiology and Biostatistics in Clinical Trial Center, Ajou University Medical Center, Suwon, Republic of Korea
    • ,
  • Kye Hee Cho, MD

      Affiliations

    • Department of Physical Medicine and Rehabilitation, Ajou University School of Medicine, Suwon, Republic of Korea

Article Outline

Abstract 

Yoon S-H, Rah UW, Sheen SS, Cho KH. Comparison of 3 needle sizes for trigger point injection in myofascial pain syndrome of upper- and middle-trapezius muscle: a randomized controlled trial.

Objectives

To investigate (1) the relation between needle diameter and treatment efficacy of myofascial pain syndrome and (2) the relation between needle diameter and pain intensity during injection.

Design

Randomized controlled trial.

Setting

University-affiliated tertiary-care hospital.

Participants

Volunteers (N=77) with myofascial pain syndrome affecting upper- and middle-trapezius muscles with at least 3 months' duration of pain.

Intervention

Participants were randomly assigned to receive trigger point injections on 1 side of the trapezius with a 21-, 23-, or 25-gauge needle. After a 1-time injection, participants were followed up for 14 days. Participants and the assessor were blinded for group assignment.

Main Outcome Measures

Treatment efficacy was measured with the visual analog scale (VAS; at pretreatment, and posttreatment on days 1, 4, 7, 14) for neck and upper-back pain, the Neck Disability Index (NDI; at pretreatment, and posttreatment on days 7, 14), and the Medical Outcomes Study 36-Item Short-Form Health Survey (SF-36, at pretreatment and posttreatment on days 7, 14) for health-related quality of life. Pain intensity during injection was evaluated immediately after injection with VAS.

Results

VAS scores for posttreatment on days 4, 7, and 14 decreased significantly compared with pretreatment scores in all groups; NDI scores on days 7 and 14 decreased significantly compared with pretreatment scores in all groups; SF-36 scores on days 7 and 14 decreased significantly compared with pretreatment scores in the 21- and 23-gauge needle groups; and SF-36 score on day 14 showed significant difference between the 21- and 25-gauge needle groups. For pain intensity during injection, VAS scores indicated no significant difference between the 3 groups.

Conclusions

No difference between the needle types was observed in terms of VAS or NDI, or in terms of pain intensity felt by patients during injection. In terms of SF-36 scores, injections with 21- or 23-gauge needles were found to be more effective. However, a well-controlled investigation is needed to explore the effect of needle thickness on health-related quality of life.

Key Words: Injections, Myofascial pain syndromes, Neck pain, Quality of life, Rehabilitation

List of Abbreviations: ANOVA, analysis of variance, LTR, local twitch response, NDI, Neck Disability Index, SF-36, Medical Outcomes Study 36-Item Short-Form Health Survey, VAS, visual analog scale

 

MYOFASCIAL PAIN IS pain that derives from myofascial trigger points, which are small, highly sensitive areas in muscle that are characterized by hypersensitive, palpable, taut bands of muscle that are painful to palpation, reproduce the patient's symptoms, and cause referred pain.1, 2 Several methods have been recommended for the inactivation of trigger points. The treatments commonly used for this purpose are injection or dry needling.3 The trapezius is probably the muscle that most often experiences myofascial trigger points,1 and it is a frequently overlooked source of temporal4 and cervicogenic5 headaches. Clinically, the boundary between the upper- and middle-trapezius is frequently indistinguishable by palpation and is defined only by the locations of the attachment of fibers in relation to spinous processes, the scapular spine, acromion, and clavicle.1

Because no high-quality evidence is available about the efficacy of differently sized needles for trigger point injection, physicians have based needle selection on experience and not on scientific evidence. In some textbooks1, 6 and in a review article7 on trigger point injection, thick needles (21 or 22 gauge) have been recommended for administering injections to superficial muscles such as the trapezius because although a needle with a smaller diameter may cause less discomfort, it is likely to provide neither the required mechanical disruption of a trigger point nor adequate sensation to the physician when overlying skin, subcutaneous skin, and subcutaneous tissue are penetrated.1, 7 Smaller-gauge needles may also be deflected from a taut muscular band and thus may not penetrate a trigger point.7 Nevertheless, many studies on trigger point injection in patients with myofascial pain syndrome of neck and shoulder have used a smaller diameter 25-gauge needle.8, 9, 10, 11, 12

In the present study, we selected 3 differently sized needles to determine whether different needle thicknesses affect treatment efficacy and pain intensity. Accordingly, the purpose of this study was to determine the best needle size in terms of treatment efficacy and pain intensity during trigger point injection in myofascial pain syndrome of upper- and middle-trapezius muscle. We hypothesized that thicker needles (1) are more effective at treating myofascial pain syndrome, and (2) induce more severe pain during injection.

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Methods 

Participants 

Between April 17 and May 28, 2008, eligible participants between 20 and 70 years of age with pain in the posterior neck and upper back were recruited by displaying posters in a university-affiliated tertiary-care hospital in Suwon, Korea.

The required sample size was determined by power analysis on the basis of a previous study.13 The SD of VAS score was assumed to be 20. Power calculations indicated that detecting a 20% difference in improvement in VAS score between 3 groups (with α=.05 and β=.10) would require a sample of 22 subjects for each group. To account for dropouts, 28 subjects were recruited for each group.

Study Design and Randomization 

An intention-to-treat format and a randomized controlled design were adopted; the assessor (K.H.C.) was blinded to subject group allocations. A schematic of the study is shown in figure 1. A total of 115 subjects were recruited. Of these, 31 were excluded, 29 because they met exclusion criteria and the remaining 2 because of refusal. Screening evaluations, including the diagnosis of myofascial pain syndrome, were performed by one of the authors (S.H.Y.). After screening evaluations, 84 participants were randomly assigned to 1 of 3 groups by a block randomization method, which ensured that approximately equal numbers were allocated to each group.14 A computerized random number generator and tablea were used to perform group allocations, which was managed by another author (U.W.R.).

Inclusion and Exclusion Criteria 

Inclusion criteria were: (1) participants with myofascial pain syndrome affecting the upper- and/or middle-trapezius muscles with posterior neck and/or upper-back pain, (2) a duration of pain of at least 3 months, (3) pain of moderate to severe intensity, defined as a score of 30 points or more on an ordinal self-rating pain scale rated from 0 (no pain) to 100 (worst imaginable pain). Exclusion criteria were: (1) receiving anticoagulant medication, (2) receiving an antiplatelet agent within 3 days before study commencement, (3) having pain related to trauma within 6 months of this study commencement, (4) receiving a trigger point injection within 3 months of this study in the same region, (5) receiving posterior neck and upper-back pain–related treatment, with the exception of oral medication, (6) having a diagnosis of fibromyalgia syndrome, cervical radiculopathy, or myelopathy, (7) having a history of cervical or shoulder surgery, (8) having any other medical or psychologic condition, including cancer, rheumatoid arthritis, endocrine disease, major depression, or schizophrenia, and (9) having obesity, defined as a body mass index of 27.5 or higher. All patients provided written informed consent before enrollment.

Intervention 

The diagnosis of an active myofascial trigger point was based on the criteria described by Simons et al1: tender spots in 1 or more palpable taut bands, a typical pattern of referred pain, palpable or visible LTR (defined as a transient contraction of muscle fibers in a tense band associated with a trigger point) during snapping palpation at the most sensitive spot in the taut band, and a restricted range of motion in terms of lateral bending of the cervical spine to the opposite side.1 Trapezius muscle depths (skin to the lower border of the trapezius) were measured by ultrasoundb to ensure that the needle lengths were sufficient to reach and disrupt contraction knots at trigger points. Participants were treated by the standard trigger point injection procedure, as described by Simons.1 Treatment began with a subject lying on his or her side or semiprone with the involved side uppermost.

Three types of needles were used in this study. The 21- and 25-gauge needles were chosen because they are generally recommended or used in research studies for trigger point injections.6, 8, 9, 10, 11, 12 In addition, a needle size (23 gauge) in between the 2 sizes was selected for this study for comparison. The 23- and 25-gauge needles were 1in long and the 21-gauge needlesc 1.25in long; injections were made with a 3mL syringe filled with 0.5% lidocaine. Up to 3 of the most painful trigger points in the right or left trapezius muscle were injected per subject. The stretched band localized between the index and the third finger was entered rapidly with the tip of the needle perpendicular to the skin. The needle was inserted into the muscle until the exact trigger point was reached. After injecting 0.1mL of lidocaine solution, the needle was moved backward and forward, and the same point was needled 6 to 8 times. After injection, the injected area was compressed firmly for at least 10 minutes to achieve hemostasis. Then the trapezius muscle was lengthened by manual stretching. Participants were instructed to perform a home exercise program that involved stretching and strengthening the posterior neck and upper-back muscles, and they were encouraged during each visit to continue with the home exercise program. Palpations and injections were conducted by one of the authors (S.H.Y.) who had 10 years of experience at diagnosing and treating myofascial pain syndrome.

Participants were allowed to continue taking their regular medications, including analgesics, anti-inflammatory medication, and muscle relaxants, but they were asked to record their dosages. Participants were monitored and asked not to begin any new medications related to pain control after study commencement. After this one-time injection, participants were followed for 14 days, and asked to visit on days 1, 4, 7, and 14, when they were asked to report any event that might have a significant effect on satisfaction or quality of life. A total of 7 study participants were excluded from the analysis (3 in the 21-gauge needle group, 3 in the 23-gauge needle group, and 1 in the 25-gauge needle group): 3 participants did not attend follow-up, the spouse of 1 participant died, 2 participants received other treatments for neck pain (one an injection and the other heat therapy) at other clinics, and 1 participant was no longer interested. Accordingly, the final analysis was performed on 77 participants. The study was approved by the institutional review board at the hospital.

Outcome Measurements 

Assessment of treatment efficacy 

Treatment efficacy was evaluated by one of the authors (K.H.C.). To reduce bias, this evaluator and the participants were not informed of the gauges of needles used. Face-to-face interviews were used to evaluate VAS scores, and a self-reported questionnaire was used to evaluate NDIs and SF-36 scores.

VAS was used as the primary outcome measurement to measure posterior neck and upper-back pain, and scores ranged from 0 (no pain) to 100 (worst imaginable pain). VAS has been validated as a reliable, generalizable, and internally consistent measure of clinical and experimental pain.15 VAS scores were obtained pretreatment, and on days 1, 4, 7, and 14 posttreatment. Participants were asked to indicate the average pain level that they had experienced over the previous 24 hours.

NDIs ranged from 0 to 50, where 0 represented minimum disability and 50 represented maximal disability, and these were determined pretreatment and at days 7 and 14 posttreatment. SF-36 scores were rating from 0 to 100, where 0 represented poorest health and 100 best health, and these were determined pretreatment and at days 7 and 14 posttreatment. The administered questionnaire evaluated effect of the disease on well-being and functional status by asking patients to self-rate 36 items that measured 8 health domains, and a single item that measured changes in self-perceived health.16 The SF-36 is one of the most widely used physical and mental health status instruments and is increasingly being used for measuring outcomes in patients with pain.17, 18 It has established reliability and validity in chronic pain disorders,19, 20, 21 and it includes 8 health concepts: (1) limitations on physical activities because of health problems, (2) limitations on social activities because of physical or emotional problems, (3) limitations on usual role activities because of physical health problems, (4) bodily pain, (5) general mental health (psychologic distress and well-being), (6) limitations on usual role activities because of emotional problems, (7) vitality (energy and fatigue), and (8) general health perceptions. In the present study, we calculated physical and mental component scale scores by using the recommended norm-based scoring procedure.22 The translation of the Korean version of the SF-36 was developed by means of a standard methodology by the International Quality of Life Assessment Project.23

Assessment of pain intensity during injection 

Pain intensity was evaluated immediately after trigger point injection with the VAS. The author (who conducted the injection) also observed whether needling elicited any LTR.

Statistical Analysis 

We compared the 3 study groups in terms of sex, employment, and trigger point location by performing chi-square analysis. Repeated measures ANOVA was used to assess overall group effects, time effects, and group-by-time interaction effects. The paired t test and Bonferroni correction were applied to within-group comparisons of treatment efficacy. One-way ANOVA was used to compare the 3 study groups before and after treatment. One-way ANOVA was also used to compare the 3 groups with respect to pain intensities during injection. Furthermore, all 3 groups were subgrouped with respect to LTR, and subgroups were then compared by the independent t test. All of the above analyses were performed by SPSSd statistical software. Significance was accepted for P values of less than .05. Multiple comparison adjustments were assessed.

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Results 

There were no significant differences between the 3 groups in terms of demographic and clinical characteristics at baseline (table 1).

Table 1. Baseline Demographic and Clinical Characteristics of the Participants
Characteristics21G (n=25)23G (n=25)25G (n=27)P
Age (y)51.0±11.0(32–69)49.6±11.4(32–70)53.9±11.9(26–70).388
Disease duration (mo)27.1±24.9(3–90)44.4±44.9(3–180)37.2±49.5(3–204).338
BMI (kg/m2)23.6±2.3(19.1–27.2)23.4±2.2(19.5–27.1)23.5±2.4(18.8–27.4).965
VAS score at pretreatment59.5±10.3(40–80)52.8±13.0(30–75)54.9±12.5(30–75).138
NDI score at pretreatment13.2±6.0(3–29)13.8±5.5(6–30)13.6±5.8(3–32).928
SF-36 score at pretreatment54.4±20.4(12–90)54.8±16.3(24–80)57.3±14.4(14–74).798
Sex (M/F)6/193/223/24.368
Employment (nonworking/working)2/236/194/23.294
Location of trigger point (dominant/nondominant)15/1014/1120/7.360

NOTE. Values are mean ± SD (minimal value–maximal value) or n. None of the differences was significant (P>.05).

Abbreviations: BMI, body mass index; 21G, 21-gauge needle group; 23G, 23-gauge needle group; 25G, 25-gauge needle group.

Treatment Efficacy 

The average pretreatment scores ± SD of all 77 participants were as follows: VAS, 55.7±12.15; NDI, 13.5±5.70; and SF-36, 55.5±17.0.

Visual analog scale for neck and upper-back pain 

In the 21-gauge needle group, mean pretreatment VAS score (day 0) was 59.5±10.3 and posttreatment VAS scores were 51.9±21.5, 36.0±19.8, 30.8±23.9, and 23.0±18.3 on days 1, 4, 7, and 14, respectively. In the 23-gauge needle group, mean pretreatment VAS score was 52.8±13.0 and posttreatment VAS scores were 43.8±21.4, 27.6±16.5, 25.8±19.1, and 25.1±24.8 on days 1, 4, 7, and 14, respectively. In the 25-gauge needle group, mean pretreatment VAS score was 54.5±13.4 and posttreatment VAS scores were 58.2±20.9, 39.7±20.3, 29.3±18.3, and 28.2±22.9 on days 1, 4, 7, and 14, respectively (fig 2). Repeated measures ANOVA demonstrated no significant interaction between groups and time (P=.155). VAS scores showed a significant decrement in pain over time for all 3 groups (P<.001), but no differences were observed between groups (P=.195). In the 21-gauge needle group, no significant difference was observed between VAS scores on day 0 and day 1 (paired t test, P=.096), but significant differences were found between day 0 and days 4, 7, and 14 (paired t test, all P<.001). In the 23-gauge needle group, no significant difference was observed between VAS scores on day 0 and day 1 (paired t test, P=.080), but significant differences were found between day 0 and days 4, 7, and 14 (paired t test, all P<.001). In the 25-gauge needle group, no significant difference was observed between VAS scores on day 0 and day 1 (paired t test, P=.329), but again, significant differences were found between day 0 and days 4, 7, and 14 (paired t test, all P<.001). Therefore, in all 3 groups, VAS scores on days 4, 7, and 14 posttreatment were significantly lower than on day 0. No significant difference was observed between VAS scores in the 3 groups on days 0, 1, 4, 7, or 14 (1-way ANOVA, P=.138, P=.056, P=.069, P=.684, P=.698, respectively). Therefore, all groups showed postinjection VAS improvements in neck and upper-back pain on days 4, 7, and 14 versus pretreatment levels, and no difference was found between the groups.

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  • Fig 2. 

    Mean changes of VAS score at pre- (day 0) and post- (days 1, 4, 7, 14) treatment. A negative change indicates a more favorable result. There were significant differences of VAS score at posttreatment on days 4, 7, 14 compared with pretreatment in all groups. There were no significant differences between 3 different needle size groups at pre- and posttreatment on days 1, 4, 7, 14. No statistically significant differences between 3 different needle size groups at pre- and posttreatment on days 1, 4, 7, 14 (P>.05). Mean values and SE are shown. *Statistically significant difference compared with pretreatment (P<.013).

Neck Disability Index 

In the 21-gauge needle group, mean NDI on day 0 was 13.2±6.0 and on days 7 and 14 were 8.7±4.5 and 7.7±4.5, respectively. In the 23-gauge needle group, mean NDI on day 0 was 13.8±5.5 and on days 7 and 14 were 9.6±5.5 and 9.6±5.3, respectively. In the 25-gauge needle group, mean NDI on day 0 was 13.6±5.8 and on days 7 and 14 were 10.3±7.2 and 10.4±6.5, respectively (fig 3). Repeated measures ANOVA demonstrated no significant interaction between group and time (P=.695). In analyses of effects within groups, NDI showed a significant decrement over time (P<.001). However, no significant effect was observed between the groups (P=.490). In the 21-gauge needle group, significant differences were observed between mean NDIs on day 0 versus days 7 and 14 (paired t test, respectively, P=.003, P<.001). In the 23-gauge needle group, significant differences were also observed on day 0 versus days 7 and 14 (paired t test, P<.001, P=.003, respectively), and similarly, in the 25-gauge needle group, significant differences were also observed on day 0 versus days 7 and 14 (paired t test, all P=.002). Therefore, in all groups, NDIs on days 7 and 14 were significantly lower than pretreatment values. However, no significant differences were observed between the 3 groups on days 0, 7, or 14 (1-way ANOVA, P=.928, P=.630, P=.217, respectively). Therefore, all 3 groups showed postinjection improvements in neck disability on days 7 and 14, and no difference was observed between the groups.

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  • Fig 3. 

    Mean changes of NDI score at pre- (day 0) and posttreatment (days 7, 14). A negative change indicates a more favorable result. There were significant differences of NDI score at posttreatment on days 7, 14 compared with pretreatment in all groups. There were no significant differences between 3 different needle size groups at pre- and posttreatment on days 7, 14. No statistically significant differences between 3 different needle size groups at pre- and posttreatment on days 7, 14 (P>.05). Mean values and SE are shown. *Statistically significant difference compared with pretreatment (P<.025).

The SF-36 for general health status 

In the 21-gauge needle group, mean SF-36 score on day 0 was 54.3±20.4 and on days 7 and 14 SF-36 scores were 67.8±18.0 and 69.8±16.4, respectively. In the 23-gauge needle group, mean SF-36 score on day 0 was 54.8±16.3 and on days 7 and 14 scores were 64.1±16.1 and 64.0±16.5, respectively. In the 25-gauge needle group, mean SF-36 score on day 0 was 57.3±14.4 and on days 7 and 14 scores were 60.3±17.3 and 58.2±12.8, respectively (fig 4). Repeated measures ANOVA demonstrated a significant interaction between group and time (P=.005), and changes in SF-36 scores with time appeared to depend on needle thickness. In the 21-gauge needle group, significant differences were observed between day 0 and days 7 and 14 (paired t test, P=.001, P<.001, respectively), and in the 23-gauge needle group, significant differences were also observed between day 0 and days 7 and 14 (paired t test, P<.001, P=.002, respectively). However, in the 25-gauge needle group, no significant difference was observed between day 0 and days 7 and 14 (paired t test, P=.358, P=.727, respectively). No significant difference between the 3 different needle size groups was observed in terms of SF-36 scores on day 0 or day 7 (1-way ANOVA, P=.798, P=.295, respectively). However, a significant difference was observed between the 21- and 25-gauge needle groups on day 14 (1-way ANOVA, P=.028). Therefore, the 21- and 23-gauge needle groups showed postinjection improvements in general health status on days 7 and 14.

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  • Fig 4. 

    Mean changes of SF-36 at pre- (day 0) and posttreatment (days 7, 14). A positive change indicates a more favorable result. There were significant differences in SF-36 score at posttreatment on days 7, 14 compared with pretreatment in the 21- and 23-gauge needle groups. But in the 25-gauge needle groups, there was no difference in SF-36 score at posttreatment on days 7, 14. There were no significant differences between 3 different needle size groups at pre- and posttreatment on day 7. There were significant differences between the 21- and 25-gauge needle groups at posttreatment on day 14. Mean values and SE are shown. *Statistically significant difference compared with pretreatment (P<.025). †Statistically significant difference between the 21- and 25-gauge needle group on day 14 (P<.05).

Pain Intensity During Injection 

Mean VAS scores for pain intensity during injection were 60.5±19.8 in the 21-gauge needle group, 56.2±20.0 in the 23-gauge needle group, and 56.3±16.2 in the 25-gauge needle group, showing no intergroup differences (1-way ANOVA, P=.696). Comparisons between the subgroups, with or without LTR, were undertaken to determine whether the occurrence of LTR during injection is related to pain intensity, but no significant intragroup differences were found (independent t test, P=.247 in the 21-gauge needle group, P=.090 in the 23-gauge needle group, P=.582 in the 25-gauge needle group, and P=.173 for all participants) (table 2). Mean distances from skin to the lower margin of the trapezius muscle was 16.4±3.6mm (range, 10.5–24.8mm) in the 21-gauge needle group, 15.9±2.8mm (10.0–21.5mm) in the 23-gauge needle group, and 16.5±3.3mm (9.9–24.2mm) in the 25-gauge needle group, showing no significant intergroups difference (1-way ANOVA, P=.872).

Table 2. Pain Intensity During Injection Between Needle Size and Subgroups With or Without LTRs
21G23G25GTotal
VAS score during injection (0–100) (n)60.5±19.8(25)56.2±20.0(25)56.3±18.5(27)57.6±18.5(77)
LTR, elicited62.6±21.9(16)60.0±20.4(16)57.1±18.0(20)60.0±19.7(52)
LTR, not elicited56.8±16.0(9)49.6±18.5(9)54.3±10.2(7)53.5±15.3(25)

NOTE. Values are mean ± SD. No statistically significant difference between groups and within group according to with or without LTR (P>.05).

Abbreviations: 21G, 21-gauge needle group; 23G, 23-gauge needle group; 25G, 25-gauge needle group.

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Discussion 

The present study was undertaken to determine optimal needle size in terms of treatment efficacy and pain intensity during trigger point injection in myofascial pain syndrome of upper- and middle-trapezius muscle. No difference between needle types was observed in terms of neck or upper-back pain (VAS) or neck disability (NDI), or in terms of pain intensities felt by patients during injection. However, injection with 21- and 23-gauge needles, rather than 25-gauge needles, was found to be more effective in SF-36. To investigate the generalizability of our results, we reviewed the findings of previous studies on chronic neck and upper-back pain of myofascial origin. Average pretreatment VAS scores were as follows; 47.7±15.2 (n=15) and 60.6±20.0 (n=14),13 69.0±14.3 (n=10),9 67.0±13.2 (n=8),24 and 49.48±28.55 (n=33),25 average pretreatment NDI scores were 13.0±6.3 (n=8),24 29.4±12.1 (n=32),26 and average pretreatment SF-36 scores were 43.7±15.1 (n=14) and 54.9±20.2 (n=15).13 The average pretreatment score of participants in our study showed milder disease severity than previous studies.

In the present study, we used 3 types of patient-reported outcomes, which are measures of subjective symptoms. These measurements provide a better understanding of treatment outcomes from the perspective of patients by translating clinical improvements into patient-perceived outcomes; however, these measurements alone are not sufficient to evaluate treatment efficacy objectively. Thus, it is important to identify the minimum clinically significant changes of these patient-reported measures. Minimum clinically significant change is used to indicate relevant changes in clinical practice,27 and the minimum clinically significant change of a VAS score is defined as the mean difference between one score and the preceding VAS score when a subject reports little, less, or slightly more pain.28 The minimum clinically significant change for VAS pain severity was determined to be 13 points28; therefore, studies addressing pain experiences with less than a 13 VAS point difference, although statistically significant, may be of no clinical importance. A change in score of 2.6 SE29 or change scores of 3.5 for NDI27 were needed to achieve minimum clinically significant change. In terms of SF-36, a score difference of 5 points is considered clinically relevant.30 We evaluated our results on the basis of the criteria of these studies28, 29, 30: score changes of VAS on days 4, 7, and 14 in all the groups achieved the minimum clinically significant change; score changes of NDI on days 7 and 14 in all the groups achieved the minimum clinically significant change; score changes of SF-36 on days 7 and 14 in the 21- and 23-gauge needle groups achieved the minimum clinically significant change. Therefore, these findings appeared to be compatible with the statistical significances of the treatment efficacy.

We initially hypothesized that the thick needles improve treatment efficacy on the basis of the findings described in previous literature reviews,1, 7 which concluded that larger-diameter needles are less prone to bending within tissues and thus provide more accurate sensation of tissue textures being penetrated. On the other hand, thinner needles are more flexible and are thus more likely to bend because of the dense nature of the contraction knots, which represent trigger points, and cause less tissue damage during repeated penetrations.1 Their small outer needle diameters may make it difficult to cause sufficient mechanical disruption.31, 32 Contrary to these opinions, we found no differences between the 3 needles examined in terms of VAS-assessed posterior neck and upper-back pain, which was the primary outcome measurement, or in terms of neck disability (NDI). However, SF-36, which measures general health status, revealed that the 21- and 23-gauge needles showed significant differences in within-group comparisons, whereas the 25-gauge needle did not. SF-36 was used in this study to evaluate changes in general health status and in health-related quality of life. SF-36 measures pain-related behavior, whereas VAS measures pain, and in the present study, the use of thicker (21 and 23 gauge) needles was found to be more effective at improving behavioral dysfunction. Furthermore, depression commonly coexists in patients with chronic pain (16%–90%),33, 34, 35 and it has been reported that SF-36 reflects depression severity in these patients.36, 37 Accordingly, we postulate that thicker needles also alleviate chronic pain–related behavioral dysfunction and depression. However, these explanations are not sufficient enough to explain the difference only in SF-36, with no statistical difference in VAS as the primary outcome measurement between 3 groups. Therefore, we suggest that a well-controlled investigation be conducted to explore the effect of needle thickness on health-related quality of life.

All the results in this study are presented as mean changes in VAS, NDI, and SF-36 scores, and these scores have large SDs. Therefore, it is difficult to track individual patient changes during treatment, and identifying the percentages of patients who reached a clinically significant target would help draw meaningful conclusions. On the basis of previous studies,24, 38 we set a clinically significant target as at least a 50% decrease in VAS, a 30% decrease in NDI, and 20% increase in SF-36 from baseline. Our results show that many participants who received injections with a 21-gauge needle, particularly on day 14, appeared to reach a clinically significant target (table 3). This implies—although no significant difference in VAS scores or NDIs was achieved—that treatment may have been more effective when a thicker needle was used.

Table 3. Percentage of Subjects Who Reached a Clinically Significant Target
Target21G (n=25) (%)23G (n=25) (%)25G (n=27) (%)
VAS⁎
Day 748.052.044.4
Day 1468.060.051.9
NDI†
Day 756.052.040.7
Day 1468.044.048.1
SF-36‡
Day 752.044.037.0
Day 1460.040.040.7

Abbreviations: 21G, 21-gauge needle group; 23G, 23-gauge needle group; 25G, 25-gauge needle group.

⁎Defined as at least 50% decrease compared with pretreatment.

†Defined as at least 30% decrease compared with pretreatment.

‡Defined as at least 20% increase compared with pretreatment.

Previous studies indicate that various contributory factors can affect pain intensity during injection, such as velocity,39, 40 angle of insertion,39 depth of injection,41 needle diameter,39, 42 needle tip bluntness,43 regional variation,44 and activated nociceptor density.40 Jorgensen42 suggested that thinner needles induce less injection pain, but another study that used an automated and controlled needle insertion device found that although needle diameter could affect pain intensity when the skin is repeatedly needled, pain intensity for a single cutaneous needle insertion is not significantly related to needle length or diameter.40 Unlike previous studies,39, 40, 41, 42, 43, 44 which investigated the intensity of pain caused by skin damage by single or repeated subcutaneous or intradermal injections, trigger point injections may have different contributing factors because repeated injections to muscle, along with single skin insertion, are the main causes of pain. We considered that LTR originating from muscle and fascia might also contribute to pain during trigger point injection. To investigate the relationship between LTR and pain, we divided the participants into subgroups, with or without LTR, but found no significant differences. Physicians tend to hesitate to use thick needles because they think that thick needles cause more pain. However, the results of the present study reveal that LTR during trigger point injection and needle diameter did not greatly affect pain intensity. Because pain is one of the main reasons why patients fear a trigger point injection, future studies should focus on identifying the factors that are responsible for pain.

The present study, which was conducted in nonobese participants (body mass index<27.5), indicates that a needle length of at least 1in is required to penetrate the trapezius muscle. In the present study, the maximum depth recorded was 24.8mm, and the average for all total participants was 16.3±3.2mm. Furthermore, conducting a trigger point injection in obese patients would require a longer needle. Although these arguments cannot be taken to serve as concrete guidelines, we recommend that needles of less than 1 inch be avoided.

In our literature review, the present study is the first to investigate the effect of needle diameter on treatment efficacy and pain intensity during trigger point injection in myofascial pain syndrome of upper- and middle-trapezius muscle. Because there is little high-quality evidence available regarding the efficacy of different needle sizes, physicians can only rely on the belief that thicker needles, although effective, cause more pain. However, the present study provides concrete evidence that 21-, 23-, and 25-gauge needles are no different in terms of treatment efficacy for neck and upper-back pain (VAS) and neck disability (NDI), and that needle size in the range examined has no effect on subjective pain intensity during injection. In addition, it was found that the elicitation of LTR was found to be unrelated to pain intensity.

Study Limitations 

This study has several limitations. First, there was no placebo or control group, and thus, changes in VAS, NDI, and SF-36 could have been due to cointerventions or other factors not related to the injections. Second, subjects were recruited at a single hospital, which poses problems in terms of the generalizability of our findings. Third, patients were followed up for only 14 days. Fourth, the trapezius muscle was lengthened by manual stretching immediately after injection and participants were instructed to continue home exercise program; however, compliance was inadequately monitored. Fifth, to evaluate treatment efficacy, we used 3 types of patient-reported outcome tools, that is, VAS, NDI, and SF-36, which measure subjective symptoms, and thus, the study lacked fully objective measures, such as number of trigger points, changes in loci, and pressure pain threshold measured by pressure algometry.

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Conclusions 

This study carried out a 1-time trigger point injection with 21-, 23-, or 25-gauge needles in participants with myofascial pain syndrome of upper- and middle-trapezius muscle who were then followed up for 2 weeks. No difference among the needle types was observed in terms of neck or upper-back pain (VAS) or neck disability (NDI), or in terms of pain intensities felt by patients during injection. In terms of SF-36 scores, injections with 21- or 23-gauge needles, rather than 25-gauge needles, were found to be more effective. However, a well-controlled investigation is needed to explore the effect of needle thickness on health-related quality of life in patients with myofascial pain syndrome.

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  • a Stat Trek Inc; available at: http://stattrek.com/Tables/Random.aspx.
  • b Logiq P6; GE Healthcare Ultrasound Korea Ltd, 65-1 Sangdaewon-dong, Sungnam, Korea.
  • c Korea Vaccine Ltd, 87-3 Garak-dong, Seoul, Korea.
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 No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit on the authors or on any organization with which the authors are associated.

PII: S0003-9993(09)00274-3

doi:10.1016/j.apmr.2009.01.028

Archives of Physical Medicine and Rehabilitation
Volume 90, Issue 8 , Pages 1332-1339, August 2009

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