Division of neuromuscular compartments and localization of the center of the intramuscular nerve-dense region in pelvic wall muscles based on Sihler's staining

The innervation of the pelvic wall muscles is not very clear. This study aimed to reveal the division of neuromuscular compartments and localize the surface position and depth of the center of the intramuscular nerve-dense region (CINDR) of the pelvic wall muscles based on Sihler's staining. Twenty-four adult cadavers were used. To localize the CINDR of the pelvic wall muscles, horizontal (H) and longitudinal (L) reference lines were drawn, and Sihler’s staining was used to reveal the intramuscular nerve distribution. The CINDR projection points (P and P′ points) behind and in front of the body surface, the positions of the P points projected onto the H and L lines (P_H and P_L points), and the depth of CINDR were determined by spiral computed tomography scanning. The piriformis and obturator internus muscles can be divided into two and three neuromuscular compartments, respectively. The P_H of CINDR of the piriformis muscle was located at 22.61 ± 2.66% of the H line, the P_L was at 28.53 ± 6.08% of the L line, and the puncture depth of the piriformis muscle was at 24.64 ± 2.16% of the PP′ line. The P_H of CINDR of the obturator internus muscle was at 16.49 ± 1.20% of the H line, the P_L was at 10.94 ± 1.09% of its L line, and the puncture depth was 6.26 ± 0.38 cm. These findings may guide the design of the compartmentalized transplantation of the pelvic wall muscles and improve the target localization efficiency and efficacy for injecting botulinum toxin A to treat pelvic wall muscle spasm.