Cervical radiculopathy (CR) is a group of signs and symptoms indicating compression of the cervical spinal nerve root [1], and it is associated with numbness, pain, loss of sensation, and can seriously affect quality of life [2]. The prevalence of CR has previously been reported to range from 1.07 to 1.76 per 1,000 for males, and 0.63 to 5.8 per 1,000 for females, and peaks in the 4th and 5th decades in life [3,4]. It was reported last year that with changes in people’s work and lifestyles, the incidence of CR has increased [5].

Treatment guidelines recommend: surgery, traction, medication, massage, acupuncture, moxibustion, and/or physical therapy [6]. In the last decade there has been an increased rate in surgery for CR, however, there is no accurate indication for surgical CR [7]. In addition, 4% of patients who undergo surgery suffer postoperative side effects [8]. Without surgery, more than 75% of patients’ symptoms significantly improve within three months of conservative treatment [7]. Among the conservative methods used in clinical practice to treat CR, thread embedding acupuncture (TEA) is one of the most effective and is attracting attention in Korea [9].

The principle of TEA is based on the theory of acupuncture and moxibustion and is where thread continuously stimulates the acupoint where it has been embedded. The threads used stimulate tissues (such as skin, muscles, ligaments, and tendons) to induce an immune reaction to treat the patient’s condition. TEA is useful for various conditions/diseases that require long-term acupoint stimulation, especially neurogenic, musculoskeletal, and visceral pain-related conditions/diseases [10]. However, despite the use of TEA treatment for CR in clinical trials, few studies have reviewed the treatment effects of TEA for CR. A systematic review of TEA for CR was conducted in 2020 in China [11], but with a limited selection of literature, little analysis and minimal quality evaluation. In this study, to determine a consensus for the direction of clinical research on TEA for CR, clinical effectiveness and safety were evaluated by analyzing the acupoints, tools, and embedding methods used.

Search strategy

There were 16 databases searched, including 4 English language databases (PubMed, EMBASE, Cochrane Library, and Google Scholar), 2 Chinese databases [China National Knowledge Infrastructure (CNKI) and the Wanfang databases], 2 Japanese databases (CiNii and J-stage), and 8 Korean databases [KISS, ScienceOn, KMbase, KoreaMed, Koreascience (KISTI), OASIS, RISS, and Korean Traditional Knowledge Portal (KTKP)]. No restrictions on country, language, or publication date were imposed on the searches which were performed up to August 22, 2022.

In the international databases the following search terms were used: [(“cervical” OR “neck”) AND (“radiculopathy” OR “nerve root” OR “neck and arm pain”) AND (“catgut” OR “thread” OR “needle” OR “acupuncture” OR “acupoints”) AND (“implant*” OR “embed*” OR “embedding therapy” OR “maesun” OR “maeseon”)]. In the Chinese and Japanese databases, the search terms were inputted in both English and Chinese/Japanese. In the domestic databases (assuming that there would be few studies) the search terms “maesun” or “maeseon” (which means TEA in Korean) were used. Different synonyms were combined to perform searches according to the characteristics of the database used.

Document screening and data extraction

Two researchers independently performed the search according to the inclusion and exclusion criteria and preliminary selection was made after reading the article titles and abstracts. Duplicates were removed, and the remaining articles full text was read to ensure relevant content.

The extracted content included items such as researchers, year of publication, number and gender ratio of treatment and control groups, mean duration of illness, intervention with two groups, outcome indicators, results, dropouts, and adverse events (AEs). Details of TEA and control interventions according to the Standards for Reporting Interventions in Clinical Trials of Acupuncture (STRICTA) [12] were also extracted.

In cases of disagreement, a 3rd researcher participated in discussion, consultation, and decision-making, and if necessary, contacted the authors of studies to obtain further information on the studies.

Eligibility criteria

The inclusion criteria were as follows: (1) Studies should be randomized controlled trials (RCTs) reported in domestic and foreign journals (we included RCTs with no specific delineation of the randomization methods referred to simply as “random allocation”); (2) studies on patients with CR, regardless of race, gender, or severity and duration of disease; (3) treatment groups treated with TEA (which could include interventions that differed from the control group, except for TEA, with no restrictions on control interventions); and (4) studies conducted in any country or language, with any publication date.

The exclusion criteria were as follows: (1) non-RCT, quasi-RCT, case report, and systematic review studies; (2) duplicate research, obvious data errors or data failure; (3) no use of a control group in the study design; (4) exclusion of needle embedding therapy, such as press-needle or intradermal acupuncture, if TEA was not performed on the treatment group; (5) exactly the same TEA conditions used for both treatment and control groups, making it impossible to compare the effects of TEA between groups; and (6) theses.

Quality assessment

Two reviewers independently evaluated the risk of bias in the selected literature. If no agreement was reached, a 3rd party intervened, and the decision was made by majority vote. The Cochrane’s risk-of-bias tool (ROB) 2 was used as an evaluation tool for quality assessment and the NECA Systematic Literature Review Manual [13] was used as a reference. ROB 2 contains assessment fields that relate to “low risk,” “unclear risk,” or “high risk” of bias, including random sequence generation, allocation concealment, blinding of participants and personnel, blinding of outcome assessment, incomplete outcome data, selective reporting, and other biases. If we applied random allocation but did not describe specific random methods, such as random number tables, computers, dice, or coin use, the output was an “unclear risk.” For incomplete outcome data, if there was no mention of dropouts, but the criteria for elimination were presented, bias was deemed to be “low risk.” Regarding reporting bias, if the presence or absence of adverse reactions was not mentioned, it also led to a determination of “unclear risk.”

Study search results

A total of 2,644 articles were retrieved from 16 databases. After eliminating 2,586 articles that did not meet the eligibility criteria, 34 duplicate records were also removed. Of the remaining 24 studies, 2 were excluded because they used the same TEA methods in both the treatment and control group. Twenty-two articles [14–35] were included in the final review (Fig. 1).

Basic characteristics of the studies

There were 22 studies included in the review which were published between 2010 and 2021. A total of 2,483 individuals were included in this review, and the characteristics of the studies are shown in Table 1 [14–35]. Each trial used between 60–360 patients. The gender distribution could not be determined due to some RCTs not reporting the gender ratio. The duration of CR symptoms ranged from 1 month to 9 years but duration was not reported in three studies. None of the studies differed significantly regarding general information such as sex ratio, age, and morbidity period between groups before treatment. Three studies experienced dropouts [14,21,30]. Thirty-five dropout cases were reported overall, including 21 in treatment groups and 14 in control groups. All trials were conducted in China of which, one study was written in English [14]. Four studies involved three-arm parallel trials [14,17,21,33], and the remainder all involved two-arm trials. All patients in the studies were diagnosed with CR.

Materials

The most frequently used materials in the studies were catgut (eight studies; [16–18,21,23,24,28,32]), followed by polyglycolide-lactide (PGLA; 7 studies; [14,15,26,27,29,33,34]), polydioxanone (PDO; 4 studies; [20–22,25]), chromic catgut (1 study: [19]), and collagen (1 study; [30]). Two studies [31,35] only mentioned the manufacturer of the absorbent surgical suture without specifying the material.

Size and length of the TEA tools

Regarding the size of the TEA tools, the range of thread length 0.5–3 cm, with an average of 1.3 cm. The most frequently used length was 1 cm. Two studies made no mention of thread length [16,19]. The thickness of the thread used was based on United States Pharmacopoeia (USP) monographs ranging from USP 4-0 to USP 2. The most frequently used thickness was USP 2-0 in eight studies, followed by USP 4-0 in seven studies.

Regarding the length of embedding needles, only two studies mentioned that used 4 cm [20] and 6.9 cm [29] needles the other studies did not mention the length of the needle used. A few studies explicitly mentioned the diameter of the needle, and most of them reported the standard numbers. The diameters of the needles were 0.3–0.9 mm, but most studies preferred 0.9 mm-diameter needles (No. 9 needles in 10 studies).

Treatment sites

The most frequently used acupoint in TEA was EX-B2, which was used in 18 of the 22 studies. Although two studies did not specify an acupoint, they used a local region near the cervical spine as a treatment site [17,24]. The remaining two studies expected a therapeutic effect from inserting medical threads into distal acupoints in the abdomen [23] or hand [30] without using local acupoints in the treatment group. The 2nd most used acupoint after EX-B2 was GV14, which was used in 13 studies. Ashi points were also used as local acupoints. The most used distal acupoints were BL12, LI4, LI11 (each used in five trials), followed by GB20, BL11, BL15, SI3, and GV20 (each used in four trials). Many of the studies used acupoints determined by pattern identification.

Treatment frequency and duration

The frequency of TEA was once every 7 to 15 days. The most common frequency was once a week [14,15,20,22,25,26,30,33,34], followed by once every 14–15 days [19,21,23,24,27,29,31,35] and every 10 days [16,17,32]. TEA was administered 2–4 times, and 2 times was the most frequent (10 studies), followed by 3 times (7 studies), and 4 times (3 studies). Two studies did not report the frequency or number of sessions. The total TEA treatment period was 2–6 weeks. The most common period was 28–30 days (9 studies), followed by 21–22 days (5 studies), 2 weeks (4 studies), 45 days (2 studies), and 6 weeks (1 study). One study did not specify the duration of treatment.

Outcome measures

Of the 22 studies, 18 studies used efficacy rates based on 3 or 4 criteria: full recovery, significant effect, moderate effect, and no effect (some studies did not use the “significant effect” category). Based on these criteria, they all reported total efficacy rates, meaning the percentage of the total minus the “no effect” cases. Full recovery rates were also reported [17–19]. The 2nd most frequently used outcome measure (applied in 16 studies) was the visual analog scale (VAS), which allows the patient to indicate on a scale of 0 to 10 the level of pain they are experiencing. Nine studies used the Neck Disability Index (NDI), seven used Yasuhisa Tanaka 20 (YT-20), four used the Pain Rating Index and Present Pain Index, and one study used the Northwick Park Neck Pain Questionnaire. Besides the above-mentioned evaluation indicators, some studies used measures such as the Short Form 36-Item Health Survey [14], analgesic effective rate [23], cervical range of motion [32], range of motion score [24], and symptom score [31], as shown in Table 2 [14–35].

Experimental intervention

All the studies included in this review used TEA as an experimental intervention. Five studies used TEA in both treatment and control groups [14,19,21,33,34]. Two compared TEA depths [14,33] and one compared different TEA materials [21]. The other two studies compared different TEA insertion methods [19,34], including an accompanying ultrasound guide [34] and different types of embedding needles [19].

Concomitant treatment

Herbal medicine [16,28,32], was the most commonly used concomitant treatment with TEA. Cervical traction [19,28], nerve blocks [24,29] and acupotomy (AP) [17,18] were also used. Cervical thermotherapy, neurotrophic therapy [28], digital acupoint pressure [23], and acupuncture and moxibustion treatment [30] were also used with TEA.

Control intervention

Acupuncture treatment alone was the most common control intervention in 12 studies [15,16,20–27,32,35], but 1 used electroacupuncture (EA) [31] and 1 used both acupuncture and moxibustion treatment [30]. Nerve blocks [29], AP [17,18], Western medicine symptomatic treatment including cervical thermotherapy, neurotrophic therapy, and cervical traction [28] and sham TEA [14] were also applied as control interventions.

Therapeutic effects

Comparison with sham TEA

One study by Chu et al [14] compared sham TEA with real TEA. Real TEA patients were assigned into a middle-layer acupoint PGLA embedding (MAPE) group and a deep-layer acupoint PGLA embedding (DAPE) group. Sham TEA involves threadless insertion at the same acupoint and depth as DAPE under ultrasound guidance. Sham TEA showed no significant change before and after treatment according to any of the evaluation indicators (p > 0.05). For all evaluation indicators, DAPE, and MAPE showed significant improvement compared with sham TEA after treatment.

Comparison of different TEA depths

Two studies performed TEA at different depths. Sun et al [33] assigned patients into shallow, middle, and deep layer TEA, and Chu et al [14] assigned patients into middle and deep layer TEA combined with ultrasound guidance. The shallow layer group had threads planted subcutaneously, the middle layer group had threads planted in the semispinalis capitis, and the deep layer group had threads planted in the multifidus. Based on all result indicators (VAS, NDI, YT-20, Pain Rating Index, and Present Pain Index), TEA was more effective in the DAPE group compared with the shallow-layer acupoint PGLA embedding (SAPE) group. MAPE was more effective than SAPE according to all indicators except YT-20. A comparison of DAPE with MAPE showed that DAPE had significantly better or similar therapeutic effects to MAPE.

This study analyzed 22 RCTs (2,483 patients) that reported the efficacy and safety of TEA for CR. Studies were selected from 16 domestic and international databases, to August 22, 2022. Recently, one review on TEA for CR was published [11] and concluded that TEA had a better therapeutic effect than acupuncture or EA, but had more AEs (subcutaneous congestion) than acupuncture. However, the quality and number of RCTs reviewed were low. This review examined a larger number of studies and conducted various analyses.

Considering the basic features of TEA used in the studies (in China), catgut was (and continues to be) the most widely and consistently used material. However, according to Feng et al [21], catgut caused a higher incidence of pain, redness, and induration than PDO. Huang et al [36] observed that severe AEs, such as necrosis, skin ulcers, and suppuration, occurred mostly with the use of catgut or chromic catgut. Changing the materials used in TEA in China may be advisable. In Korea, catgut has been reported to be less safe than PDO or PGLA, so it is rarely used, and most clinicians use PDO [37].

Regarding the size of TEA tools, the thread lengths used were short (0.5–3 cm), with an average length of 1.3 cm. Thread diameters were thick, ranging from USP 4-0 to 2, and the most frequently used diameter was USP 2-0 (i.e., 0.3–0.339 mm) [9]. The embedding needles were thick. No. 9 needles (0.9 mm diameter) were used most often, but the needle length was rarely reported. In China, the thickness of the embedding needle is usually marked with a standard number; therefore, Chinese studies rarely specify a diameter. Jun et al [38] mentioned that in China, the No. 6 needle was a diameter of 0.6 mm, and No. 7 needle was a diameter of 0.7 mm. Based on this, the diameter of the needle was analyzed. However, in Korea, the threads used are mostly 2.5–9 cm long and 0.069–0.149 mm thick (USP 7-0 to 5-0), with 25G (diameter 0.5 mm) to 30G (diameter 0.26 mm) needles [9]. Therefore, the studies included in this review, which were conducted in China, used thicker and shorter threads with thicker needles than is typical in Korea. The TEA tools seem to differ from typical Korean tools due to the specificity of the insertion method. In China, when embedded into acupoints, the medical threads are cut short and inserted with tools, such as plungers [38]. Therefore, the findings determined from this review seem difficult to apply it to the situation of domestic research in Korea.

The main treatment sites for CR were local acupoints, especially EX-B2 and GV14. Two studies [23,30] administered treatment using distal acupoint properties without local acupoints. When distal acupoints alone were treated, the treatment had a more significant effect than the control group, which used local points. It would be interesting for more studies to use distal acupoints in the future.

The usual frequency of TEA was once every 7–15 days, and once a week was the most common. The total treatment period for TEA ranged from 2–6 weeks, and 28–30 days was the most common.

Regarding concomitant treatment, many of the studies combined herbal medicine, cervical traction, nerve blocks, and AP with TEA. This is worth examining further in TEA-related RCTs or in clinical practice. Generally, acupuncture is the easiest cotreatment with TEA for treating CR. However, among the studies on TEA for CR, no research has compared acupuncture alone with acupuncture combined with TEA. Therefore, more research is necessary.

The most frequently used outcome measure in this review was the total efficacy rate. This rate is mainly based on Chinese medical diagnostic evaluation and is divided into “full recovery,” “significant effect,” “moderate effect,” and “no effect.” Based on this, the total efficacy rate indicates ratios higher than a “moderate effect.” The “full recovery” rate can also be measured. This reflects the subjectivity of the evaluator or the patient and involves only three or four evaluations. Therefore, the reliability or discrimination power of total efficacy rate can be lower than indicators evaluated by a score, such as the VAS or NDI [11]. In addition, each study described the definitions and efficacy evaluation criteria slightly differently, reducing the objectivity of the studies. Therefore, there is a need to standardize the efficacy evaluation criteria for CR and cervical condition/disease. The 2nd most frequently used outcome measures were the NDI and VAS. These are considered objective, detailed, and simple but user-friendly numerical scales. Therefore, scales like these should be used in future studies.

Various studies have compared the therapeutic effects of TEA. Sham TEA, with only the thread missing from real TEA, was an ineffective treatment compared with real TEA, where it was possible to compare the effects of the thread. Since sham TEA resembles acupuncture in that only the needle is inserted and removed, this is consistent with the results that TEA was more effective than acupuncture [15,20–22,25–27,35]. Comparing the depth of needle insertion used for TEA, the depths were divided into shallow layer (subcutaneous), middle layer (semispinalis capitis), and deep layer (multifidus), the deeper the TEA, the better the treatment effect was in most of the cases [14,33].

When comparing TEA materials, catgut and PDO showed no observed difference in the effectiveness of treatment, however, catgut was less safe [21].

Regarding TEA implementation methods, ultrasound guidance had significantly fewer side effects and better therapeutic effects compared with the conventional method [34]. It seems that the use of an ultrasound guidance targets the intended structure and depth of cervical muscles more accurately. However, a more specific description of the method, such as the angle of entry, and in-plane, out-plane would be valuable.

The use of a flat blade needle as an embedding needle, which resembles AP, was significantly better than the use of a conventional embedding needle [19]. TEA tools like this would be useful for domestic introduction in Korea. It is also necessary to develop various types of TEA.

Single TEA was better than single acupuncture [15,20–22,25–27,35], and the results were consistent with the conclusion of a previous review on TEA for CR [11]. However, many studies have applied similar designs and acupoints, so more diverse approaches are needed.

When compared with other remedies, TEA was also better than EA [31]. TEA combined with AP was better than single AP or single TEA. There was no significant difference between single AP and single TEA [17,18]. In some studies, concomitant treatment that was not used in the control group was performed alongside TEA in the treatment group [16,23,24,28,32]. In these cases, although the studies concluded that the experimental groups showed improvement, it is difficult to determine whether the therapeutic effect was due to concomitant treatment or TEA.

Regarding safety, five studies [14,27,29,31,34] reported side effects; only 2% (6 out of 281 patients) who received TEA had mild to moderate side effects, and no serious AEs were reported. Although many studies did not indicate AEs, considering that 281 people in 5 RCTs is a considerable number, it seems that TEA is relatively safe. However, future TEA studies conducted on CR patients should report the AEs of treatment.

Regarding the risk of bias, only half of the 22 studies described specific random allocation methods. Concerning allocation concealment, blinding of participants, and outcome assessment, no studies made any mention of them, except one study [14]. Trials with inadequate or unclear allocation concealment can produce up to 40% larger estimates of treatment effects [39]. In the case of performance bias, concealment may be difficult due to the nature of the treatment, but researchers should attempt to minimize selection and detection bias to improve the quality of research. Only four studies mentioned dropouts [14,21,27,30], only five studies mentioned AEs [14,27,29,31,34], and the remainder gave no indications. In addition, a few studies did not compare VAS scores as expected [31], did not report the significance of the results [17], or made no mention of the frequency and number of treatments [18]. Overall, many details were omitted, making it difficult to judge the risk of bias.

This review has several limitations. Due to differences between the acupoints, methods, and manipulations of TEA, there may be considerable heterogeneity in this study’s results. Most of the RCTs in this review were published in China using Chinese; hence, language bias may have been introduced due to the problem of language interpretation. Although the number of studies included in this review was limited, TEA seems to be an effective treatment for CR. However, more research is needed to draw definite conclusions. RCTs should be conducted and carried out in strict compliance with the Consolidated Standards of Reporting Trials (CONSORT) Statement [40] and standardized reporting. The selection and reporting of appropriate patients, populations, interventions, comparisons, and outcomes (PICO) should be based on PICO standards [41]. High-quality RCTs with a low risk of bias on TEA treatment of CR should be conducted.

Based on 22 studies that considered TEA treatment for CR, TEA appeared to be a safe treatment and may effectively relieve pain in CR patients. However, there were some limitations to this review due to unreported or omitted data, language, concomitant treatments, and the heterogeneity of the included studies.

Flow chart of document retrieval and screening.

Risk of bias in the included studies.

Risk-of-bias summary.

Characteristics of the Included Studies.

Results and Adverse Events of the Included Studies.