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BL52 is located 3 cun lateral to the lower border of the spinous process of the L2 vertebra. The needling pathway includes the skin, subcutaneous tissue, latissimus dorsi muscle, intrinsic muscles of the back, quadratus lumborum muscle, the dorsal branches of the second lumbar artery and vein, and the lateral branches containing fibres from the second lumber spinal nerve.1 Deep perpendicular needle insertion at this location in the lower back risks damage to the kidneys,2 which are located in the dorsal region of the abdominal cavity within the retroperitoneal space.
In 2015, we observed the needling depth at BL52 on the right side of 13 cadavers during the eighth week of medical student anatomical dissection teaching at Flinders University of South Australia (table 1). The left sides of the cadavers were not included, because they had already been dissected by the medical students. The cadavers were donated through the Body Donation Program to the school for teaching and research purposes. None of them were Australian Aboriginal or Torres Strait Islanders. Ethical approval was granted by the Southern Adelaide Clinical Human Research Ethics Committee (reference no. 245.14—HREC/14/SAC/241).
In each cadaver, a caudal-cranial sagittal dissection was performed to expose the lumbar vertebra. The interspace of L2/3 was located by visually counting the vertebra. Then, the cun measurement of each individual cadaver was obtained by measuring the width of its thumb, which was used for localisation of BL52 at the level of L2/3. Next, the depth-measuring blade of a vernier caliper was inserted dorsally and perpendicularly to the surface of the skin at BL52 to mimic acupuncture needle insertion until the deepest layer was perforated. A vernier caliper was used in order to provide precise measurement to the nearest 1 mm. The needling depth was defined as the depth at which the blade passed through all the tissue layers and entered the abdominal cavity, and the safe depth was defined as 75% of the needling depth;3 that is, safe depth increases proportionately with needling depth. The procedure was carried out by KLC, who is an experienced registered acupuncturist.
Needling depth at BL52
All needles inserted dorsally and perpendicularly at BL52 perforated the quadratus lumborum muscle (figure 1). In general, male subjects had a greater needling depth than female subjects (median 37 (IQR 24–59) mm vs 30 (21–46) mm). Therefore, the safe depths in males and females were estimated to be 28 (18–44) mm and 23 (16–35) mm, respectively. Overall needling depth was 32 (25–47) mm and the safe depth was 24 (18–35) mm for male and female subjects combined.
To our knowledge, there have been two previous published observations of needling depth at BL52. In 1998, a study of 51 cadavers in China suggested that the overall needling depth was approximately 32–35 mm.3 In 2003, another study of 10 cadavers in China reported that the overall needling depth was about 28 mm.4 Needling depth at BL52 in the present (third) study was similar in magnitude.
The safe depth of 24 (18–35) mm suggests that the tip of the needle will typically lie between quadratus lumborum and latissimus dorsi after insertion (figure 1). This observation suggests that needles at BL52 come into close proximity with lumbar spinal nerves, which travel anteriorly between the quadratus lumborum and latissimus dorsi muscles before entering the plane between the internal oblique and transversus abdominis muscles. Thus, needling at this site may stimulate the somatic and sympathetic nervous systems to induce local and systemic effects.5
Our observation showed that the overall needling depth and safe depth at BL52 were 32 (25–47) mm and 24 (18–35) mm, respectively, in Australian cadavers.
Contributors KLC was responsible for the original idea of this research, study design, ethics application, data collection, statistical analysis, discussion of the research findings, and preparation of the manuscript. RVH was responsible for supervision, provision of expert opinion about the research, and discussion of the research findings. Both authors examined and approved the final manuscript.
Competing interests None declared.
Ethics approval Southern Adelaide Clinical Human Research Ethics Committee.
Provenance and peer review Not commissioned; internally peer reviewed.
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