Dear Editor:
There are two types of recommended needling depth for acupoints—a Westernized approach that studied cadavers or medical images to establish a safe insertion depth as quantified in mm,1 and a more-traditional approach that used a directional (cun) method in which 1 cun is defined as the width of the interphalangeal joint of a given individual's thumb. Thus, the cun method is a relative measurement specific to individual persons. The cun-based needling depth for a given acupoint, however, is occasionally different in standard textbooks used for teaching acupuncture. Because of this, the nonstandardized depths may cause uncertainty about the efficacy and safety of acupuncture treatments. For instance, for acupoint BL40 (Fig. 1), located at the midpoint of the popliteal crease of the posterior knee, the recommended depth is 0.5 cun in Japan,2 0.5–1 cun in Taiwan,3 0.5–1.5 cun in China,4 and 1 to 1.5 cun in the United Kingdom.5 The popliteal vein and artery are anatomically underneath the BL 40 point and relevant vascular injuries with severe clinical features have been reported.6,7 Thus, we investigated the relationship between the cun-based depths (0.5, 1, and 1.5 cun) and relative risks of the popliteal vein being penetrated.
FIG. 1.
Placement of the BL 40acupoint.
We conducted a preliminary magnetic resonance imaging (MRI) study that captured a sagittal MRI (Fig. 2) and an axial MRI (Fig. 3) on the knee region of dominant legs of healthy young subjects: 5 men and 4 women (body mass index = 21.6 ± 1.6; ages = 27.5 ± 4.6). Using the resultant MRI images, the distance between BL 40 at the top of the skin and the popliteal vein was measured (Fig. 3), then the measured values (in mm) were compared to the individual subject's cun (mm). A rather consistent pattern was seen, 0.5-cun and 1-cun needling (10.2 ± 0.8 mm, 20.4 ± 1.7 mm, respectively) was safe for all of the subjects, while 1.5-cun needling (30.7 ± 2.5 mm) could have potentially gotten inserted into the popliteal vein in 5 out 9 subjects (56%; 4 men and 1 woman).
FIG. 2.
Sagittal magnetic resonance imaging displays the relative positions of the popliteal vein and the BL 40 point.
FIG. 3.
Axial magnetic resonance imaging displays the relative positions of the popliteal vein and the BL 40 point.
It is of clinical importance that the needles should not be inserted deeply at BL 40 to minimize the risk of a penetrating injury of the popliteal vein underneath. Bleeding resulting from the insertion might lead to the popliteal vein with resultant stasis and local thrombosis, or the insertion may dislodge a preexisting thrombosis.7 Based on our preliminary finding, needling at BL 40 using 1-cun or a shorter depth is preferable.
Acknowledgments
Ikuro Wakayama, MD, PhD, Hirohisa Oda, PhD, Kyota Narita, LAc, and Mrs. Mikiko Gokan, LAc provided expertise and insight that to assist the authors in writing this Letter.
References
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