Localization of nerve entry points and the center of intramuscular nerve-dense regions in the adult pectoralis major and pectoralis minor and its significance in blocking muscle spasticity.

The aims of this study were to localize the body surface position and depth of nerve entry points, and the center of the intramuscular nerve-dense regions of the pectoralis major and pectoralis minor in order to provide guidance for blocking muscle spasticity. Formalin-fixed adult cadavers (66.3 ± 5.2 years) were used. The curved line on the skin from the acromion to the most inferior point of the jugular notch was defined as the horizontal reference line (H). The line from the most inferior point of the jugular notch to the xiphisternal joint was defined as the longitudinal reference line (L). The nerve entry points was anatomically exposed. Sihler's staining, barium sulfate labeling, and computed tomography were employed to determine the projection points (P) on the body surface. The intersection of the longitudinal line through the P point and the H line and the horizontal line through the P point and the L line were recorded as PH and PL , respectively. The projection of the nerve entry points or the center of the intramuscular nerve-dense regions were in the opposite direction across the transverse plane and were recorded as P'. The percentage positions of PH and PL on the H and L lines, as well as the nerve entry points and the center of the intramuscular nerve-dense regions depths, were determined using the Syngo system. The pectoralis major had two nerve entry points, while the pectoralis minor had only one. In addition, two intramuscular nerve-dense regions were found in the pectoralis major, while only one region was found in the pectoralis minor. The PH of the nerve entry points were located at 47.83%, 32.31%, and 34.31%, while the PH of the center of the intramuscular nerve-dense regions were at 41.95%, 55.88%, and 32.58% of line H, respectively. The PL of the nerve entry points were at -9.84%, 36.16%, and 2.44%, while the PL for each of three center of the intramuscular nerve-dense regions was at -3.87%, 25.29%, and -7.13% of line L, respectively. The depth for each of the nerve entry points was at 17.76%, 17.53%, and 25.51% of line P-P'', respectively, and the depth of the center of the intramuscular nerve-dense regions was at 5.23%, 6.75%, and 13.73% of line P-P', respectively. These percentage values are all means. The definition of the surface position and depth of these nerve entry points and center of the intramuscular nerve-dense regions can improve the localization efficiency and efficacy of target blocking for pectoralis major and minor spasticity.