Introduction

Dry needling (DN) therapy uses a thin filiform needle to penetrate the skin and stimulate underlying myofascial trigger points (MTrPs) and muscular, and connective tissues. Dry needling is defined by Western medicine as a type of acupuncture [1]. Acupuncture has been adopted to modern physiotherapy practice based on anatomy, neuroscience, pathology and evidence-based medicine, and has been integrated into the Western medical model [2]. Western medical model acupuncture is now quite commonly used in the treatment of soft tissue injuries within physiotherapy practice [3]. According to Fan et al.(2017), DN can be considered an equivalent of acupuncture, and traditional acupoints are equivalent with trigger points (dry needling points) [4]. In a literature review with implications for clinical practice guidelines, Dunning et al.(2014) noted the terms acupuncture and dry needling were used interchangeably, and stated that dry needling requires the insertion of thin monofilament needles, as used in the practice of acupuncture [5]. According to Guan-Yuan JIN et al. (2016), dry needling is a type of “contemporary acupuncture because the needles and needling techniques used in dry needling and acupuncture are the same [6]”. Also, Zhu and Most (2016) indicated that dry needling practitioners, such as physical therapists who are not acupuncturists, use the same needles [1]. However, the use of dry needling by physical therapists is not based on ancient theories or tenets of traditional Chinese medicine (TCM) which uses techniques such as acupuncture. A commentary by The American Alliance for Professional Acupuncture Safety (AAPAS) states that dry needling is a subset of acupuncture [7]. Dry needling is used to treat muscles, ligaments, tendons, subcutaneous fascia, and scar tissue [5]. Various explanations of dry needling mechanisms and effects have been proposed. Dunning et al. mention biomechanical, chemical and vascular effects of needling into either superficial subcutaneous tissue (non-muscular) or deep (intramuscular tissue) at trigger point and non-trigger point locations [5]. The potential effects include pain relief, wound healing acceleration, and changes in the neuromyofascial system. Superficial dry needling (SDN) involves insertion of the needle into the subcutaneous tissue, but not the muscle, and seems to adequately address scar tissue.

Scar formation results from wound healing processes that occur following physical injury to body tissues. Prolonged and abnormal wound healing may cause the development of hypertrophic scars which can be itchy and painful, resulting in serious functional disabilities and/or cosmetic defects. It has been suggested that local application of needles around the scars effectively facilitates the scar healing process and alleviates pain and other scar-related symptoms [8]. Therefore, there is a need to continue research to verify the efficacy of local management with needling for scar tissues. This systematic review aimed to assess the usefulness of dry needling or local acupuncture for scar treatment. To identify all relevant scientific papers the terms ‘acupuncture,’ ‘needling,’ or ‘dry needling’ were used in the search process. Practical aspects of dry needling or acupuncture in the local management of different scar types were discussed. In the latter case, we limited our selection to papers describing acupuncture applied locally, mainly in the scar setting.

Methods

An a priori systematic review protocol was developed and registered at the International Platform of Registered Systematic Review and Meta-analysis Protocols. The registration number is INPLASY 202310058 [9].

This systematic review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 statement [10].

Inclusion and exclusion criteria for the review

The research question was defined according to the PICO criteria (Table 1). The eligibility criteria were developed by two reviewers (D.C. and M.N.).

Table 1 Inclusion and exclusion criteria defined by the PICO format used in the selection process to identify relevant publications
Full size table

Information sources

MEDLINE (PubMed, EBSCOHost and Ovid), EMBASE (Elsevier), and Web of Science databases were searched for relevant publications by two lead reviewers (D.C. and M.N.). The databases were searched from their inception until the last entry, between October 5 and 10, 2023. To minimize the risk of relevant sources omission, the strategies to explore Google Scholar were implemented (M.K).

Search strategy

As mentioned above, the terms needling, dry needling and acupuncture have been used interchangeably. Therefore the search strategy included different combinations of the following keywords: ‘scar’, ‘keloid’, ‘dry needling’, ‘needling’, ‘acupuncture’, ‘treatment’, ‘physical therapy’.

Search strategies for all databases (see Additional file 1) were developed by two reviewers (D.C. and A.O.B.), who gained knowledge in this area through video tutorials and close cooperation with an experienced librarian from the Medical University Library.

Selection process

All search results were compared; duplicate publications were removed manually by two independent researchers (D.C and M.N.). The ultimate outcome was again compared.

Forms I and II (see Additional file 2) based on inclusion and exclusion criteria were prepared for stages 1 and 2 of the study selection process. Explanation and elaboration documents (see Additional file 3) were also prepared. During the title-abstract stage, two reviewers (D.C. and A.O.B) made independent decisions based on the eligibility criteria presented in Form I to select the retrieved articles. Titles and abstracts lacking sufficient information regarding inclusion criteria specified in Form I were obtained as full texts. Where only the title was available (no abstract), but indicated compliance with the inclusion criteria, the paper was included in stage 2, where the full texts were reviewed. Form II was filled out, and a decision on inclusion of the full text in this systematic review was made. Full texts were independently screened by two reviewers (D.C. and A.O.B.). The reference lists of papers meeting the inclusion criteria were independently searched by two other researchers (M.N. and J.M.) to identify additional relevant studies.

At both stages of the paper selection process, discrepancies between the reviewers regarding eligibility were discussed until a consensus was reached. In cases of uncertainty, an additional reviewer (M.K.) was consulted to make a definitive decision.

Data collection process

Two reviewers (D.C. and M.N.) collected data from all included studies using a customized data extraction table in Microsoft Excel. They independently copied appropriate extracts from the full texts and pasted them into the table. In the final version of the table, the data extracted by both authors were compared and verified by another researcher (J.M.). In case of disagreement, all three authors debated until a consensus was reached.

Data items

Data extracted from each study included information related to basic publication characteristics (first author, publication year, country/countries of the research center) and study-specific data (study design, aim of the study, type of scar, sample size, group/s), characteristics of the intervention (e.g. needling technique, needle: diameter, length), its location, manual needling manipulation, number of sessions, setting, outcomes and results. The results were extracted based on the study type.

Quality assessment. Risk of bias analysis

Assessment of the methodological quality of each study was performed depending on study design. For randomized controlled trials (RCTs), the Physiotherapy Evidence Database (PEDro) score was used to assess the risk of bias and methodological quality of the trials. The Physiotherapy Evidence Database (PEDro) scale consists of 10 questions pertaining to the internal validity and statistical information provided [11]. The total PEDro Scale score is 10 points. Based on the PEDro score, the methodological quality of trials was rated as excellent (PEDro scores 9–10), good (6 to 8 ), fair (4 to 5) or poor (≤ 3) [12]. Two reviewers (D.C. and M.S.) independently assessed the methodological quality of the articles included in this systematic review. In controversial cases, consensus was sought by involving a third researcher (J.M.) [13].

The JBI Critical appraisal tools developed by the Joanna Briggs Institute (JBI) and collaborators, and approved by the JBI Scientific Committee were used for case reports and for case series (https://jbi.global/critical-appraisal-tools). All papers selected for inclusion in this systematic review were subjected to appraisal by two independent reviewers (D.C. and M.S.).

Data analysis and synthesis

Due to between-study differences regarding certain aspects of treatment and ways to evaluate treatment effects, this systematic review descriptively summarised and analysed the findings from the included studies.

Results

Selection of sources of evidence

A total of 924 publication titles and abstracts were identified by searching the electronic databases. After removing duplicates (n = 102), 822 records remained. Google Scholar handsearch yielded another 3 papers. In addition, after scanning the references, one paper was identified as eligible for full-text screening [14].

All details of the selection of the sources of evidence, including the reasons for exclusion at the full-text stage, are presented in the PRISMA flow diagram (Fig. 1). The titles of two papers extracted from the electronic databases indicated acupuncture in scar therapy [15, 16]; despite the lack of an abstract, these studies were included in the full-text stage. Following full-text screening (see Additional files 2 and 3), 6 studies were excluded [16,17,18,19,20,21] and 11 out of 17 publications were considered eligible for this review. Of the 11 publications included in the final review, eight are case reports [14, 15, 22,23,24,25,26,27], two are randomized clinical trials [28, 29], and one is a case series [30].

Fig. 1
figure 1

PRISMA diagram flow for the study search and selection

Full size image

Quality assessment

The JBI Critical appraisal tools were used for case reports included in our review. Two studies scored 2–4 out of a total of 8 points on the JBI checklist [15, 23], five studies scored 5–7 [14, 22–25], and only one study scored 8 points [27] (Table 2). Two low-quality case reports were published as brief reports [15, 23]. Moderate-quality (5–7/8) case reports did not provide information regarding presence or absence of adverse effects of the treatment or unanticipated events were not identified [14, 24, 26]. Only three case studies monitored the risk of side effects of locally performed acupuncture [22, 25, 27]. In three case reports the post-intervention clinical condition was not clearly described, which had an effect on quality assessment (5/8) [23,24,25]. In some studies, details regarding treatment parameters were not clearly presented [14, 23, 25].

Table 2 Eight case reports on the effectiveness of dry needling or acupuncture for scar treatment - assessed using the Joanna Briggs Institute (JBI) appraisal tools
Full size table

Table 3 summarizes the methodological quality of the two randomized clinical trials that were included in our review and rated with the PEDro scale. The methodological quality of these trials was rated as good [28] and fair [29].

Table 3 Publications on the effectiveness of dry needling or acupuncture for scar treatment rated with the Physiotherapy Evidence Database (PEDro)
Full size table

The case series study [30] scored 7 of 10 points on the JBI checklist (Table 4).

Table 4 One case series on the effectiveness of dry needling or acupuncture for scar treatment - assessed using the Joanna Briggs Institute (JBI) appraisal tools
Full size table

Characteristics of sources of evidence

Two original peer-reviewed research articles published in 2001 [28] and 2011 [29], eight case reports [14,15,16,17,18,19,20,21,22,23,24,25,26,27] published from 2011 to 2022 and one case series [30] published in 2023 were included in the final analysis. The RCTs were from Japan [28] and China [29] (Table 5). The case reports were from the USA [24], UK [26], China [25], Indonesia [22], India [23], Australia and New Zealand [27] and Northern Ireland [14]. The case series was from Poland [30]. In one study the country of origin was not specified [15] (Table 5). The title and/or abstract of one case report (1/8) and one case series included the term dry needling [23, 30]; the term needling was used in one paper [25] while six used the term acupuncture [14, 15, 22, 24, 26, 27]. RCTs titles and/or abstracts included the terms acupuncture [29] and intradermal needling [28].

Table 5 Studies included - dry needling or acupuncture for scar treatment
Full size table

Postsurgical scars were investigated by Fang [24], Tuck [26], Huang et al. [25], Bintoro and Helianthi [22], Das and Khan [23], Kotani et al. [28], and Lubczyńska et al. [30]. Song [29] treated hypertrophic post-operative and post-injury scars; Tuckey et al. [27] discussed acupuncture for burn scars, Hunter [15] and Anderson [14] for keloids (Table 5).

One of the RCTs included 70 individuals [28]; the other RCT comprised 80 subjects [29] (Table 5). The case series included 11 individuals but one participant was excluded from the study due to initiation of the other treatment [30]. The authors of one case report mentioned there was no blinding or sham acupuncture [26]. The remaining case studies provided no information regarding patient or practitioner blinding. RCT studies were randomized [28, 29]. Kotani et al. mentioned that the assessor had been blinded [28]. Only one study provided information on the therapist’s experience in acupuncture [24].

Characteristics of the intervention

Two studies used dry needling [23, 30] and six studies used local acupuncture as the primary scar treatment [14, 15, 25, 27,28,29]. Two case reports presented acupuncture to traditional points, combined with acupuncture to local points around the scar [22, 24].

In six studies, acupuncture was combined with other physical modalities including ultrasound [14, 29] and massage [27] or pharmacotherapy [26, 28]. In case series dry needling was used together with manual scar manipulation, massage, cupping, and taping [30] (Table 6).

Table 6 Studies included - dry needling or acupuncture for scar treatment
Full size table

Duration of a single session, treatment frequency, time of treatment, number of sessions, follow-up

Multiple acupuncture needles were left in situ for different time periods, i.e., 15 to 30 min [14, 22, 24, 26, 27, 29], 2 min [25], and up to 24 h [28]. Needle retention time of 24 h is characteristic for intradermal needling technique [31]. In dry needling techniques, needles were left in situ for 1 h [23]. The frequency of needling treatment sessions was 2 per week [24], 2–3 per week [25], and 5 per week [28] or once daily with 10 sessions making up one treatment course [29], and 12 sessions during 7 weeks [27] or two times per the entire protocol; at 9th and 13th session [30]. No information concerning needling frequency was provided in four case reports [14, 15, 22, 23]. The duration of treatment was 1 month [25], 4 to 5 weeks [24, 28], 7 to 8 weeks [22, 27, 29] or 3 to 4 months [14, 15]. The total number of sessions differed considerably, and ranged from one session [26], two sessions [30], 7–8 sessions [14,15,16,17,18,19,20,21,22,23], 12 sessions [22, 27], 20 sessions [28], and up to 40 sessions [29]. The total number of sessions was not given in one paper [25]. Long-term follow-up was carried out at 6 months [15], 4 and 26 weeks [28], and 1 and 2 months of treatment completion [27] (Table 6).

The needle: diameter, length, depth of insertion, angle of insertion

Needling interventions were heterogeneous. Two RCTs and five case reports provided details on needle diameter and length [14, 15, 22, 24, 26] while the remaining case studies did not [23, 25, 27, 30]. Acupuncture needle diameters were 0.15 mm [22], 0.16 mm [28], 0.20 mm [14, 15, 24] and up to 0.30 mm [29] while needle length was 5 mm [28], 15 mm [15, 22], 30 mm [26], and up to 40-60 mm [14, 29]. In two studies using dry needling the needle diameter and length were not specified [23, 30].

Two case reports and one case series did not specify the depth of needle penetration and insertion angles [15, 23, 30]. Huang [25] and Anderson [14] only mentioned needles had been inserted subcutaneously to the connective tissue beneath the scars at the smallest possible angle. One RCT did not specify the depth of needle insertion, but used oblique insertion at an angle of 15 degrees [29]. In another RCT, intradermal needles were inserted horizontally into painful (treatment group) or nonpainful points (sham group) [28]. Two case studies used superficial needling with needle insertion to depths of 1-2 mm [22] or 0.5 mm perpendicular to the skin [26]. In one case study, the depth of needle insertion was 10 mm under the skin at an angle of 45 degrees [27]. In another one, all needles were inserted about 1 cun deep at an angle of 45 degrees [24] (Table 5).

Two case reports specified the intervals at which the acupuncture needles were placed, i.e., 1 cm [15] and 2 cm [27]. In the other studies, the distance between the needles was determined by the needling technique and needle location. Needles were placed around the pain point (surrounding the dragon technique) [24, 26], into pain points [28], along the pain map determined by the patient [23], in the local area along the scar tissue with a positive VAS response [22], and at local points that induce segmental effects with consequent analgetic effects close to the scar tissue [14].

Scar needling: location, technique, manual needling manipulation

In the studies of Das and Khan [23], Tuckey [27], Kotani [28] and Song [29], needles were placed at scar margins or around the scar. The technique named ‘surrounding the dragon’ was used by Tuck [26], Fang [24], and Lubczyńska et al. [30], and the ‘circling the dragon’ technique by Hunter [15]. Fu’s subcutaneous needling parallel to scar tissues was applied by Huang [25]. In one case study, the needles were inserted alongside the scar [22]. In five studies manual needle manipulation was employed using the swaying movement [25], bi-directional rotation [24, 27], the ”lifting-thrusting” manipulation [29], or minimal stimulation [14] (Table 6).

Evaluation of the effectiveness of the therapy

Pain was evaluated using the visual analog scale [26], Likert scale [24], and numeric rating scale [22, 27, 30]. The two case reports did not give any details on pain ratings [15, 23]. In one RCT, a 10-cm VAS was used to evaluate continuous and lancinating pain intensity. The area of pain was measured, and the pressure required to identify a painful point was determined; the patients’ diaries of daily diclofenac consumption were reviewed [28] (Table 5). In most of the studies, the intervention resulted in a reduction of pain around the scar. Tuck reports no mastectomy scar pain improvement either immediately or within 2 weeks following one local session of acupuncture [26]. The patient of Fang [24] reported a decrease of pain after 8 sessions of acupuncture; the pain level dropped from 7 to 1–2 on the Likert scale ranging from 0 to 10 (Table 5). No further improvement was observed after the next two sessions and the patient decided to discontinue the therapy (Table 6). In studies on dry needling patients also reported pain relief [23, 30] (Table 6).

Scar characteristics before and after treatment were assessed using the Vancouver Scar Scale (VSS) [25], and the Patient and Observer Scar Assessment Scale (POSAS) [27, 30]. Song et al. [29] used their own scale where 0 meant no pain, no hardness and normal skin while a score of 3 points indicated serious or constant itch, cartilage-like hardness and dark red or fresh red color (Table 5). Tuckey et al. [27] used the Numerical Rating Scale for pain and itch.

Discussion

Scar healing is a natural process that occurs as the body repairs and replaces damaged skin tissue. Initially, scars appear red, raised, and sensitive to touch. Over time, the scar tissue gradually remodels and matures, becoming flatter, lighter in color, and less noticeable. While the exact timeline for scar healing can vary depending on the individual and the nature of the injury, the period during which scars are most susceptible to mechanical interventions like needling and ultrasound typically falls within the first six to 18 months after injury occurrence. During this time, the scar tissue is still in the remodeling phase and can benefit from targeted interventions that promote collagen restructuring and stimulate blood flow to the area [32]. While the human body has a remarkable ability to heal itself, there are cases where scars do not heal naturally. Several factors can negatively affect wound healing such as wound severity, infection, poor wound care, tension on the wound, underlying health conditions (e.g. diabetes or autoimmune disorders) or genetic factors causing predisposition to abnormal scarring [33]. In such cases therapeutic interventions including DN may be indicated to promote the healing process and reduce negative symptoms. DN is reported to improve the elasticity of scar tissue; the technique loosens tissues enabling various layers to slide over one another [34].

In the papers presented, the age of the scar ranged from 5 weeks [14], 3–6 months [15, 26,27,28, 30], 1 year [24], or 4 [22, 29] to 8 years [23, 25], as shown in Table 4. The authors evaluated the scar based on parameters such as pain intensity changes or tissue color changes. This limits the possibility of drawing conclusions about the usefulness of dry needling or acupuncture depending on the age of the scars.

Dry needling and acupuncture are widely believed to lessen scar-related discomfort. Abd-Elsayed et al. report acupuncture has been used for pain control in various clinical conditions associated with chronic scar-related pain [35]. Our review highlights the scarcity of scientific evidence, and RCTs in particular, indicating possible effectiveness of needling for scar thickness, redness, pliability, or restricted range of motion. A meta-analysis was not possible as only two randomized trials and eight case reports were eligible for the review; also scar assessment scales and pain severity scales were highly heterogeneous. Case report studies are known to have a high risk of bias; some do not provide all data on post-intervention clinical condition and changes in symptoms. Anderson, for example, mentioned five pre-acupuncture scar-related symptoms while therapy outcomes were assessed for two [14]. Bintoro and Helianthi did not provide any details on changes in tissue color or hardness [22]. Fang mentioned that post-acupuncture scar was probably less red in color, which indicates only subjective observations were used for scar color evaluation [24]. Das and Khan’s patient reported a 50% reduction in post-scar neuralgia in the left thigh, but it was not stated how the pain severity had been assessed [23]. Some papers had shortcomings in method description. Seven out of the eight case reports are of moderate to low quality ratings according to JBI critical appraisal tools; only one had a maximum score on JBI Checklist [27]. The analysis of the results of the papers selected for review does not clearly establish the effectiveness of acupuncture and dry needling in scar therapy.

Pain severity was assessed using a validated scale in 4 out of 8 case reports and in one RCT. Three studies used the NRS [22, 27, 30], one the Likert scale [24] (although the description indicates it was, in fact, the NRS – authors’ note) while two relied on the VAS scores [26, 28]. Twelve sessions combining Battlefield Acupuncture and Local Point Acupuncture resulted in complete resolution of pain complaints [22]. Other papers evaluating the severity of scar-related pain reported some pain reduction after the therapy; no reasons were given for therapy termination although the symptoms did not subside completely. Considering limited data on long-term follow-up, dry needling and local acupuncture cannot be considered effective in scar pain reduction.

The authors of this systematic review were interested in the impact of needling applied to the immediate scar area. Needle insertion in the scar area was used in all studies. The technique known in Chinese medicine as “surround the dragon” [3] was practiced by Tuck [26], Fang [24], Hunter [15], and Lubczyńska et al. [30]. In other research studies, needling was carried out in the immediate vicinity of the scar, around the scar or along the scar. These needling locations are recommended by acupuncturists [31] and dry needling practitioners [8]. Rozenfeld believes needles should be placed around the entire scar or, in the case of scar section being “active” or painful, around the problematic area [8]. Abbate recommends acupuncturists should palpate around the border of the scar and find two most painful places [31]. Tender points needling causes greater pain relief than applying needles to non-painful areas [36]; the same conclusions were drawn by Kotani et al. [28]. The majority of studies selected for our review identified the site of needle insertion based on pain sensation [14, 22,23,24, 26, 28],. Due to the small number and moderate methodological quality of the papers shortlisted for our review, we cannot conclude about the site of needle insertion in scar therapy in relation to the most painful areas or points in the scar region.

The evidence of the effectiveness of acupuncture therapy alone is not strong since a number of studies have combined needling with other treatment modalities including ultrasound [14, 29], massage [27] and pharmacotherapy [26, 28] or manual manipulation and massage, cupping, taping [30]. It has been confirmed massage had a positive effect on the thickness of hypertrophic and burn scars [37, 38]. The effectiveness of manual manipulation in reducing scar-related problems has been also demonstrated [39, 40]. There is extensive literature on the effects of ultrasound on tissue healing [41,42,43]. Watson emphasizes that therapeutic ultrasound can increase tensile strength and improve scar mobility by enhancing the appropriate orientation of newly formed collagen fibres and changing the collagen profile [44]. Considering the above, the results should be interpreted as a combined effect of acupuncture and ultrasound [14, 29], massage [27], manual manipulation [30] or other treatment [26, 28, 30].

Study limitations

This systematic review comprised papers presenting the outcomes of acupuncture and dry needling interventions for scars. However, we agree with Zhou et al., who concluded that although dry needling and acupuncture share similarities, they may differ in certain aspects [45]. Combining these two procedures in one review can therefore be considered a limitation. The scarcity of case reports and RCTs presenting the impact of local acupuncture, and the lack of RCTs on dry needling prevented us from reviewing these two modalities separately. The findings should therefore be interpreted with caution. Also, future reviews should include high quality multi-center trials with uniform criteria, larger sample sizes, standard treatment protocols and outcome measures.

Conclusions

This systematic review does not allow explicit conclusions on the effectiveness of dry needling or local acupuncture as a monotherapy for scars. The analyzed studies differed regarding the delivery of dry needling or acupuncture for scar treatment. Differences included treatment frequency, duration, number of treatments, selection of needle insertion sites, number of needles used, angle of needle placement, and use of manual needling stimulation. In nine of the ten studies, the dry needling or needling or acupuncture intervention resulted in a reduction of scar pain or other scar-related symptoms.

Multicentre, blinded, randomized, controlled studies on dry needling or acupuncture need to be performed to analyze their effect on scar formation, scar-related pain, and clinical symptoms.