An Exploration of the Needling Depth in Acupuncture: The Safe Needling Depth and the Needling Depth of Clinical Efficacy

1. Introduction

Acupuncture is an important part of traditional Chinese medicine and has been used for millennia of years to treat various clinical disorders based on ancient Chinese medicine theory. In recent one hundred years, acupuncture has become one of the most popular complementary and alternative therapies in the world. More than 100 million citizens in the European Union make use of complementary and alternative medicine (CAM) today. According to EICCAM files, the most commonly used CAM therapies in Europe are homeopathy, acupuncture, phytotherapy (i.e., herbal medicine), anthroposophic medicine, naturopathy, traditional Chinese herbal medicine, osteopathy, and chiropractic. In 2007, almost 4 out of 10 adults had used CAM therapy in the past 12 months. Results from the 2007 NHIS found that approximately one in nine children (11.8%) used CAM therapy in the past 12 months. Between 2002 and 2007, increased use was seen among adults for acupuncture, deep breathing exercises, massage therapy, meditation, naturopathy, and yoga in the United States [1]. Given the fact of the rising incidence of chronic disease and stress-related illness in the West, along with an expanding awareness of the unwanted side effects of pharmaceutical treatment, there has been an increased utilization of acupuncture as a contemporary health care option [2]. Acupuncture is also practiced by about 40,000 physicians in Germany [3]. One of the three most commonly used methods of CAM is acupuncture in the United Kingdom [4]. There are 12%~19% of individuals who had received acupuncture treatment in Europe [5]. A practitioner in UK reported that an estimated 10.0% of the UK population had received any CAM therapy (an estimated 6.5% had used one of the five main therapies: acupuncture, homeopathy, chiropractic, osteopathy, or herbal medicine) [6]. Acupuncture points are known as specific locations of the body that are needled during acupuncture treatment. Acupuncture points are located along meridians that have been defined by ancient writings of Chinese medicine since thousands of years ago. Traditionally, acupuncture points are localized using cun (or Tong Shen Cun) as proportional measurement. Ancient writings of acupuncture guidelines also refer to anatomical landmarks to help localize the needling position. Cuns usually used in the documents are as follows [7].

2. Methods

A comprehensive search of the literature that was published from 1991 to 2013 was undertaken using the following key words: acupuncture, acupoint, needling depth, safe depth, dangerous depth, de-qi, therapeutic effect/efficacy, and their synonyms. These terms were used to search the following databases: PubMed, EMBASE, Cochrane, Allied and Complementary Medicine (AME), The National Center for Complementary and Alternative Medicine (NCCAM), and China National Knowledge Infrastructure (CNKI) databases. Additional articles were also identified from the reference list of identified articles. Chinese journals, theses, and dissertations that we thought might be relevant to our study were hand searched. We excluded the animal studies.

3. Results

47 studies from 1991 to 2013 were recruited into the review. As there are not many researches specific for depth of acupuncture points, we tried to include as many articles as possible. Most of the studies were retrospective, nonrandomized clinical trials without control group. The characteristics of subjects, sample size, investigated acupuncture points with the associated body region/meridians, parameters used for comparison, related factors, results and suggestions/conclusions of the researches and related factors and the results and suggestions and conclusions of the researches were summarized in the following tables classified by their measuring tool, that is, magnetic resonance imaging (MRI), in vivo subjects evaluation, computed tomography scan (CT), ultrasound, and dissected specimens of cadavers, in Tables 1, 2, 3, 4, and 5. Table 6 depicts the investigations regarding clinical efficacy.

4. Discussion

To our knowledge, this is the most comprehensive research to review all the studies regarding safe needling depth and clinical efficacy of acupuncture points. We tried to include researches as many as possible to provide a solid foundation for evidence based medicine in terms of advisable needling depth when performing acupuncture treatment. Evidence based medicine allows researchers or clinicians nowadays to ask a more extensive spectrum of miscellaneous research questions such as “Is acupuncture more effective than placebo?” or “Is CAM therapy along with wonted care more effective than wonted care alone?” These issues could be dealt with through appropriate study designs.

Studies of acupuncture safety indeed need special attention to needling depth issues. For example, the relationship between the effect of acupuncture analgesia and needling direction, angle, and depth has been optimized to enhance the analgesic effect as suggested by Fan et al. The result shows that all the 3 factors are the key influences. However, studies addressed the more specific correlation between needling depth, and issues aroused from safety or clinical efficacy are still far from enough [103].

All these facts lead to discrepancy in the safe depth measurements. For example, the suggested safe depths for GV16 are 27.05–45.55 mm (using MRI images) [21], 27.73–33.39 mm (using CT images) [33], 40.08 mm (using dissected specimens) [97], and 43.46–57.42 mm (using dissected specimens) [94].

In order to lift the level of acupuncture safety, it is necessary to utilize modern imaging technology to explore the safe depth of each acupuncture point all over the human body. We should take the regional and anatomical properties of different groups of points into consideration when deciding the measuring tools. For example, MRI imaging is very suitable for the acupuncture points in the abdominal and back regions due to the excellent ability to obtain soft tissue details while CT scan images are extremely helpful when detecting chest points. Ultrasound is a convenient tool which can obtain real-time images when trying to observe the clinical efficacy simultaneously, especially applied in vivo subjects. Using direct specimen dissections of cadavers is another measuring method. After frozen, anticorrosive, positioning, and dyeing process, the original elasticity and properties of the corpse tissues have been lost; the concerns which may arise from this kind of study are that specimens are drier and smaller than living human tissues. This may lead to possible inconsistency in measured needling depth. For example, Li et al. [27] and Dong et al. [26] compared the depths of 7 points from bladder meridian and found that depths measured via in vivo CT images were greater than ones from dissections of cadavers.

The measurement of needling depth involves the detection of soft tissue mostly. Different measurement methods often result in possible discrepancies due to the characteristic of each measuring tool. For example, Fiirgaard et al. suggested that MRI is superior in estimating the volume of acoustic neuroma than CT scan and with less inter-examiner difference [104]. MRI was reported to be better in identifying suspected disease of the brain and cervical spinal cord [105]. The sensitivity for detecting bony osteolytic lesions was 51.7% for radiography, 74.7% for computed tomography, and 95.4% for magnetic resonance imaging as reported by Walde et al. [106]. Yet MRI scanogram is slightly less accurate compared with radiographic scanogram in detecting limb length differences [107].

In addition, we also found several studies discussing the divergence among different measuring tools when investigating various body tissues including adipose volume (visceral or subcutaneous), muscle thickness, bone loss, and cartilage thickness. All these body tissues are relevant to the measurement of acupuncture points. However, the results indicated that no single measuring method would be more suitable than the other one (MRI, CT, and ultrasound). There was no significant difference between CT and MRI in the measurement of adipose tissue, glenoid bone loss, hip cartilage thickness, pheochromocytoma and in vivo skeletal muscle. Ultrasound was as good as MRI in the evaluation of supraspinatus and deltoid muscle with high correlation coefficients (0.96 and 0.97, resp.). MRI was also proved to be as precise as direct cadaver measurement to evaluate adipose tissue.

There was no difference using either ultrasound or CT for the measurement of visceral fat volume. While ultrasound was as good as CT and MRI to assess intra-abdominal adipose tissue [108–117].

Some authors compared the results of MRI/CT imaging with cadavers in measuring adipose tissue [110], skeletal muscle [115], and hyaline cartilage thickness of hips [117] and found that both MRI and CT can serve as a good reference tool in the measurement. But Stevens-Simon et al. reported that the results of their study do not support the validity of ultrasound measurement of visceral adiposity as a measure of central adiposity in postpartum teenagers [118].

Consequently, the results in terms of measuring specific body tissues using different measuring methods are ambiguous and sometimes conflicting with each other. This fact may partially explain the inconsistency of needling depth of each acupuncture point as reviewed in our study.

Some authors discussed the interobserver reliability as well. Botser et al. thought that CT was found to have higher interobserver reliability than MRI when deciding the degree of femoral anteversion [119]. MRI was again found to have less interexaminer difference in calculating the soft tissue volume [104]. Both studies pointed out that some of the measuring errors may come from the man-made technical faults.

As a result, it is very difficult to obtain a general conclusion regarding safe needling depth using these results; future researches are warranted which will be discussed later in the paper.

Some theses about using MRI for safe needling depth detection we included in this study seem to have the same sample population (number, sex ratio, age, and BMI are consistent with each other) which may result in bias in the interpretation of study results. In addition, the sample size is limited to 20 subjects which lack the power for further analysis of gender, age, and body size differences.

From the review, we learn that many factors may influence the measurement of needling depth. They include gender, age, body size (such as body length, body weight, waist girth, and BMI), which side of the body, angle of needling, and so forth. Chou et al. have reviewed part of the researches previously [120]. Among these factors, body size is always considered the most significant one which complies with our general understanding that subjects with greater body size would have greater measured depth in most of the acupuncture points. However, anatomical and structural difference exists in different human body regions when we take account of the factor like BMI.

The measured depth in body region with frequent accumulation of fat would be highly correlated with BMI. BMI is the most widely used method to show the increase in fat amount in the whole body. Nevertheless, BMI does not reliably reflect the body fat composition as only body weight and length are taken into consideration [121]. Fat distribution and sexual dimorphism further explain the likely existing gender difference [122, 123]. Mathematician Nick Trefethen believes that the body mass index formula traditionally used to work out if someone is overweight is flawed, and he has come up with his own formula. And he found short people are actually more overweight than they think they are, while tall people are not as overweight as they are being told (Daily Mail. PUBLISHED: 00:08 GMT, January 21, 2013). He claimed a new method for calculating BMI, but again only body height and weight are considered as reference factors. Probably along with waist and neck girth, simple anthropometric measures could amend the weakness of BMI as a single indicator of body size.

We hereby recommend future research suggestions regarding determining the safe needling depth. Firstly, an international congress should be convened to reach unanimous agreement on the definition of safe needling depth of each acupuncture point and acupuncture point localization method for the future study design. Secondly, factors like gender, age, BMI (or other index to differentiate body sizes), right/left side of the limb, insertion angle, and de-qi should be controlled as much as possible. Subjects (maybe crossing races) should be as many as possible, and the study design should better be randomized control studies. We should try our best to cover every acupuncture point in the whole body. Thirdly, in vivo research is better than retrospective images or specimen dissections. MRI seems to be a better tool to obtain more detailed information of anatomical structures surrounding the acupuncture needle, especially the soft tissue. Fourthly, we also suggest that multicenter should collaboration be carried out to collect statistically valuable information that can be used to increase the safety of acupuncture. Difference among different measuring methods can be understood better.

When it comes to the discussion of clinical effect of acupuncture, de-qi is frequently mentioned. De-qi means a sensation that is often elicited to enhance the effect of acupuncture treatment [124, 125]. In the ancient acupuncture literature (Huangdi) Neijing chapter Suwen indicated that de-qi may have the root in subcutaneous tissue, connective tissues, and muscles layers according to variable conditions including severity of diseases. Some practitioners of acupuncture refer to de-qi as “needle grasp,” a biomechanical phenomenon characterized by an increase in the force necessary to pull the needle out of the tissue. It has been proposed that the sensation of needle grasp is due to the contraction of skeletal muscle [126] or winding of connective tissue around the needle during needle rotation [127]. By using electric impedance, Lin showed that muscle layers were the major site of de-qi in the 22 acupoints in the back [128]. The role of the nervous system in de-qi has also been well described, and some researches in this review shared their opinions as well [24, 129]. The relevant nerves can be found in certain region surrounding the acupuncture point, and it is likely that nerves are provoked during needle manipulation. As discrepancy in definition, mechanism, and location of de-qi still exists, the depth to elicit de-qi in each point and the correlation with clinical efficacy warrants, further researches.

Only limited researches addressed the needling depth with therapeutic efficacy with good designs, and were not all acupuncture points were investigated thoroughly. Lin conducted a meta-analysis of the published evidence concerning acupoint needling depths, with the aim of providing a uniform guidance. Their group’s CT scanning results indicate safe needling depths for acupoints in the back and chest for different-sized people, that is, normal, over- and underweight adults, and for sex differences (Tables 7, 8, 9, and 10) [130].

Some clinicians have shared their clinical experiences about the optimal needling depth of to treat some diseases [131]. As there are still a lot of confusions in needling depth of acupuncture points from the ancient times to the present, which has negatively influenced the standardization and international exchanges of acupuncture science, it remains to be settled as soon as possibly [132]. After convinced that acupuncture is inherently safe, how to avoid the possible associated adverse events and complications is a top priority. We should put more efforts on how to reduce the risk by starting exploring the safe needling depth as well as the depth of clinical efficacy efficiently and correctly.

5. Conclusion

From the current review we found that there is great inconsistency in terms of safe needling depths measured from different subject groups and via different measuring tools. The depths measured in each research were somehow influenced by the different measuring methods as they all have distinguished advantages/disadvantages as compared with one another. The results of related researches fail to provide the solid support to decide the best measuring tool among conventional cadaver specimens, CT, MRI or ultrasound either. The characteristics of subjects such as ethnicity, gender, age, body size, underlying diseases, and the needling details (such as needling angle, which anatomical region of the body, which side of the body, and if with de-qi) all contributed partially to the measured depths. The definition of safe depth and standard localization method should be established by standardization through international conference. There is also lack of well-designed researches to compare the therapeutic effects thus making the proper needling depth of clinical efficacy in each acupuncture point remain obscure. A well-designed clinical trial (to control variable strictly, recruit more subjects, etc.) to decide the actual and advisable needling depth for each acupuncture point, to avoid adverse effects or complications and promote optimal clinical efficacy, is a top priority. In vivo MRI imaging may serve as a good study method.

Different levels of treatment assessment of acupuncture then can be suggested by European Information Centre on complementary and Alternative Medicine (EICCAM II), that is, efficacy (is it more effective than placebo or standard?), effectiveness (is it helpful in usual care?) and efficiency (how is the cost benefit relation?).