Abstract:

Objective　To locate the nerve entry points to human obliquus externus abdominis and to observe the intramuscular nerve staining to provide morphological data for clinical application.　Methods　The nerve entry points to the muscles were located in 11 adult cadavers and Sihler’s staining technique was applied in  5 adult cadavers.    Results    The obliquus externus abdominis was innervated by the lateral muscular branches of the inferior 8 pairs of intercostal nerves. The nerve entry point to each extended muscle fiber was (1.54 ± 0.33) cm from the midpoint at where the corresponding fiber arose, and was located at the connecting line from the junction between the midclavicular line and the lower margin of the 5th rib to the junction between the posterior axillary line and the lower margin of the 11th rib cage. Sihler’s staining showed that the lateral muscular branches of the intercostal nerves innervating obliquus externus abdominis gave off small branches to the 1/3 beginning of each extended muscular fiber, and then divided into an upper branch and a lower branch, innervating the middle  third of  the serrated origin of each muscle. These 2 nerve branches branched out in the middle third of each fiber, with the upper and lower branches of two adjacent fibers anastomosed, forming a “U” shape at each mid-distal fiber, where small branches were distributed to the 1/3 of the end of each fiber. In the upper half of the external oblique muscle, the nerve branches supplied the corresponding fiber, whereas in the lower half, the distal part of upper fiber was supplied by the nerve branch (upper branch) of next fiber at the lower portion.    Conclusion   ①This study can provide clinical guidance for local anesthesia over the upper abdomen and nerve block for postoperative incisional pain; ②A “wavy” dense area with nerve branches is formed at mid-distal part of the obliquus externus abdominis from the top down; ③It is recommended that the abdominal surgical incision should not cross more than four extended muscular fibers.

Key words: Obliquus externus abdominis, 　Nerve entry point, 　Intramuscular nerve