OBJECTIVEIt is unknown whether the psoas major muscle, thought to be a key muscle for treatment of lower back pain, can be punctured at Shenshu (BL23).

METHODSTwelve dissected specimens were used for studying the needling pathway of BL23 by perpendicularly inserting the depth-measuring blade of a vernier caliper at BL23. Dimensions of psoas muscle were measured. Correlation studies were conducted. In addition, our samples were grouped by gender and underlying medical conditions for analysis.

RESULTSHalf (50%) of the needle insertions successfully punctured psoas muscle. The mean depth of needle insertion to puncture psoas muscle (Dmin) in the group with short-term underlying medical conditions was 38.0 mm (interquartile range 29.0-51.8 mm), approximately 6 mm deeper than 32.0 (29.3-42.5) mm in the group with long-term health problems (P = 0.041). The cross-sectional area (CSA) of psoas muscle in the former group was on average approximately 1.5 times that of the latter group (P = 0.04). When the data were analysed by gender, the thickness of psoas muscle in the male group was 19.0 (6.5-24.0) mm compared to 19.5 (5.8-34.8) mm in the female group (P = 0.02). The age in the female group (P = 0.04) and the body length of the total group (P =0.04) negatively correlated to Dmin.

CONCLUSIONNeedle insertion at BL23 might be able to puncture psoas muscle. Differences in the CSA of psoas muscle and Dmin were observed in groups with short-term and long-term underlying medical conditions.