Effectiveness of dry needling and injections of myofascial trigger points associated with plantar heel pain: a systematic review

All clinical trials included in this review were obtained from peer-reviewed journals investigating the effectiveness of dry needling and/or injections of MTrPs associated with plantar heel pain. Randomised controlled and quasi-experimental (an experiment that lacks either randomisation of participants or control group(s) or both) trials examining the effectiveness of trigger point dry needling and/or injections for plantar heel pain were included. The decision to include quasi-experimental trials was based on the lack of randomised controlled trials to draw evidence from; hence we attempted to obtain an overview of what was known to date. Including non-randomised trials in systematic reviews can be appropriate when there are a limited number of randomised trials available [11]. Further, Linde et al.[12] conducted a systematic review of randomised and non-randomised trials that evaluated the effectiveness of acupuncture for chronic headache and found that non-randomised trials of good quality yielded positive responses to treatment that were similar to randomised-controlled trials. The authors concluded the inclusion of high quality non-randomised controlled trials into a systematic review might add to the generalisability of the findings. Letters to the editor, opinion pieces and editorials were excluded.

A clinical trial was included if the participants were diagnosed with plantar heel pain. All participants were over the age of 18 and had experienced symptoms of any duration. A trial was only included if the participant's plantar heel pain was managed by treatment of MTrPs in the lower extremity and/or foot. The rationale for this decision was based on the assumption that some forms of plantar heel pain might occur secondary to MTrPs in plantar heel muscles (i.e. abductor hallucis and quadratus plantae) and/or referred pain from the soleus muscle [13]. A trial was excluded if the participant's plantar heel pain was associated with a vascular or neurological disease, arthritis (degenerative and inflammatory) or fibromyalgia.

Clinical trials were included if they investigated the effectiveness of dry needling and/or injections (local anaesthetics, steroids, Botulinum toxin A and/or saline) of MTrPs for plantar heel pain. Trials were excluded if they involved needling of traditional acupuncture points as the sole treatment because the relationship between traditional acupuncture points and MTrPs is unclear [14]. However, it has been suggested that there might be a correlation between MTrPs and a class of acupuncture points referred to as Ah Shi points (pain points). Ah Shi points are a class of acupuncture points positioned outside the traditional Chinese meridians and are commonly treated by traditional acupuncturists for painful conditions including muscle spasm [15]. Given the uncertainty of this relationship, we included trials that utilised acupuncture only if it was combined with dry needling or injection of MTrPs.

A trial was included if any of the following primary outcome measures were used: Visual Analogue Scale; The Foot Health Status Questionnaire; The Foot Function Index or any other health-related quality of life measure. Secondary outcome measures investigating physiological changes (e.g. joint range of motion and pressure pain threshold) following the intervention were included providing at least one of the aforementioned primary outcome measures was reported.

In April 2010 the following electronic databases were used to search the literature: Ovid MEDLINE (1950 to date), Ovid EMBASE (from 1988 to date), Ovid AMED (from inception), CINAHL (1982 to date), SPORTDiscus (from inception) and AMI (1968 to date). A full electronic search strategy from the EMBASE database is included in Table 1.

In addition, experts in the field of MTrP therapy were questioned about their knowledge of further articles not captured in the database search. The reference lists of all included articles were hand searched for trials meeting the inclusion criteria. Finally, Google Scholar and SUMsearch were searched for grey literature (information that has not been published, or if published is not readily accessible). No language restrictions were applied.

Two investigators (MC and an impartial assessor) independently scanned the title and abstracts for information fulfilling the inclusion criteria. If a decision could not be made it was retained until the full text was obtained. A full text of all potentially eligible articles was then accessed and reviewed by both assessors to ensure eligibility. Discrepancies between the two reviewers were resolved using a third assessor (KBL).

A data extraction form (see Additional File 1) was modified from an existing standardised extraction form produced by the Centre for Reviews and Dissemination [16]. The content of the form included topics relevant to acupuncture and trigger point dry needling research as recommended by the Standards for Reporting Interventions in Controlled Trials of Acupuncture (STRICTA) [17]. Relevant data (means, mean differences, standard deviations, and p values) were extracted from the selected articles by two of the investigators (MC and SEM). Any disagreement between the authors was discussed with KBL and a general consensus agreed upon.

Two reviewers (MC and an impartial assessor) independently assessed the methodological quality of the included articles using the Quality Index (QI) [18] tool, which has been shown to have high internal consistency (KR-20: 0.89), good test-retest reliability (r = 0.88) and inter-rater reliability (r = 0.75). The original Quality Index is a 27-point checklist which covers four domains: internal validity, external validity, reporting and power. The literature has not established cut off values for the Quality Index methodological quality assessment tool. Downs and Black [18] (p. 381) stated that"the value of a single global score needs to be tested by reviewers making such an assessment before rather than after using the 27 item checklist". The use of a single summary score or global score has been criticised in the literature as it might eliminate sources of heterogeneity among the results [19].

For this systematic review, three items were modified. First, for Item 10, two points were allocated to trials that utilised confidence intervals as well as p values for the main outcomes as confidence intervals provide more information regarding the magnitude and precision of a treatment effect [20]. Second, Item 25 was removed as it has been shown that case mix adjustment cannot reduce the extent of bias in non-randomised trials [19]. Finally, Item 27 was removed as a minimally important difference using the visual analogue scale has not been calculated for MTrP interventions in participants with plantar heel pain.

The inter-rater reliability of total Quality Index scores was not calculated due to the small number of trials included. Perfect agreement was recorded on all items except question 4 where there was 67% agreement between the assessors.

Table 3 presents the results from the quality assessment. All included studies were of a poor methodological quality. The total score of the Quality Index ranged from 7/27 to 12/27 with a mean Quality Index score of 10/27 across the three trials. The internal validity domain rated most poorly across the trials due to the presence of selection [24‐26], detection [24], statistical [24], performance [24‐26] and attrition bias [24]. In addition, all three trials used secondary outcome measures that were not valid and reliable.

All trials had a quasi-experimental design with pre-test and post-test measures. Imamura et al.[24] conducted a quasi-experimental trial with a non-randomised control group to evaluate the effectiveness of 1% lidocaine injections of MTrPs in combination with physical therapy or conventional therapy alone within the foot and leg (Table 4). The physical therapy component included heat application for 20 minutes and faradic stimulation over the area treated for another 20 minutes. Stretching exercises were prescribed (3 times per day for 15 seconds) after heat application. In addition, relaxation exercises were issued to some participants if required. In contrast, the control group received conventional therapy, although the details were not included.

Tillu and Gupta investigated the effectiveness of a four-week course of traditional acupuncture followed by a two-week course of trigger point dry needling combined with acupuncture. This trial was not a cross-over design in the strict sense, rather all participants received the course of treatment in the same order. In contrast, Perez-Millan and Foster [26] investigated the effectiveness of trigger point needling combined with electro-acupuncture. Tillu and Gupta [25] and Perez-Millan and Foster [26] did not include a control group for comparison (refer to Table 4 for a description of the trigger point dry needling and injection details).

The characteristics used to identify a MTrP were not described by Tillu and Gupta [25] or Perez-Millan and Foster [26], however Imamura et al. [24] used the common criteria of a taut band and local tenderness to diagnose a MTrP. In addition, three trials varied in; the muscles that were treated; the size and type of needles used; the response elicited, and the duration of needle insertion. The treatment schedules were generally similar across the trials with weekly treatments for a period of six weeks. All three trials used a visual analogue scale as the primary outcome measure, although there was variability in the secondary outcome measures used.

As clinical heterogeneity of the included trials was evident the findings of the included studies were combined using a narrative rather than a quantitative approach. As such, meta-analysis was not performed. Table 5 provides a detailed description of the mean differences between and within groups for the trial by Imamura et al. [24] and mean differences within groups for Tillu and Gupta [25] and Perez-Millan and Foster [26].

Imamura et al. [24] found a statistically significant decrease in pain for the use of 1% lidocaine injections and standard therapy for the MTrP injection group at discharge (58.4% improvement, p = 0.003), six months (67.1% improvement, p = 0.007) and two years (67.1% improvement, p = 0.002). Similarly, a statistically significant decrease in pain was found for the control group at discharge (54.9% improvement, p < 0.05, the exact p value was not reported); however there was no follow-up at six months or two years for this group. Imamura et al. [24] found a statistically significant decrease in the duration of treatment between the injection and control groups (3.4 weeks versus 21.1 weeks respectively). Importantly the only between-group comparison made in this trial was for the total duration of treatment.

The other two trials by Tillu and Gupta [25] and Perez-Millan and Foster [26] only included a treatment group and no comparison was made to a control group. Nevertheless, Tillu and Gupta [25] observed a statistically significant improvement in pain for a two-week course of dry needling and acupuncture when compared to a previous four-week period of acupuncture treatment (p = 0.047). Finally, Perez-Millan and Foster [26] found a significant improvement in pain for the use of dry needling and electro-acupuncture (p < 0.001).