Reappraisal of the anatomical diversities of the pyramidalis muscle with their potential clinical applicability: cadaveric analysis.

Abstract

The present study examined the morphology and morphometric parameters of the pyramidalis muscle (PM) in detail with their potential applicability in making midline infra-umbilical incisions and biomechanics of the linea alba. PM was examined in 51 formalin-fixed cadavers (36 males and 15 females), and based on the mode of insertion or the level of apex, the formation or shape of the muscle was classified into nine types (Mori's classification). Bilateral PM was more prevalent (39.21%) than unilateral (1.96%) (p = 0.001). All the cases showed side symmetry except one. Mori's type 7 (right PM is higher apex and the left PM with elongated origin) was the most common form. The mean length of PM in males and females was 4.51 ± 0.14 and 3.33 ± 0.12cm on the right and 4.51 ± 0.11 and 3.26 ± 0.16cm on the left side. The mean width of right-sided PMs in males and females was 1.90 ± 0.17 and 1.58 ± 0.13cm and left-sided 1.88 ± 0.14 and 1.55 ± 0.38cm. The mean of pyramidalis-pubo-umbilical index (PPI) in males and females was 32.82 ± 1.65 and 27.50 ± 1.08, respectively. The mean insertion angle was 24.56 ± 3.07 on right side and 23 ± 2.03 on the left side (p = 0.03). Male predominance existed on right- and left-sided PM length (p < 0.001 and p < 0.001), width (p = 0.001) and PPI (p = 0.001). The strong positive correlation (r = 0.83) between length and width indicates a symmetrical muscle augmentation in the two dimensions. PM is an inconsistent anatomical structure with persistent morphology. The level and angle of insertion into the linea are crucial in the biomechanics of linea alba. PPI, determining the termination level would be useful to surgeons making midline infra-umbilical incisions.