Morphological types of the external oblique abdominal muscle aponeurosis: a morphometric and histological justification

Abstract

Objective – to investigate the histological and morphometric characteristics of the external oblique aponeurosis in the region associated with the linea semilunaris (the Ambivium zone).

Materials and methods. The study included 34 women aged 22 – 54 years (mean age: 36.2±7.3 years) who underwent abdominoplasty for cosmetic defects of the anterior abdominal wall. During surgery, standardized fragments of the external oblique aponeurosis were obtained from symmetrical regions adjacent to the lateral border of the rectus sheath. Histological, histochemical, and morphometric analyses were performed, including assessment of collagen bundle thickness, width of the endotenonium and peritenonium, parameters of the microcirculatory bed, and the relative areas occupied by collagen, peritenonium, and vessels. Hierarchical cluster analysis and the k-means method were applied to systematize the identified structural variants.

Results. Morphometric analysis revealed substantial variability in the structural organization of the aponeurosis: the proportion of collagen fibers ranged from 61.1% to 91.2%, the proportion of peritenonium from 7.3% to 33.9%, and the compactness coefficient from 0.64 to 0.93. Cluster analysis enabled the identification of three morphotypes: compact (35.3%), transitional (26.5%), and disorganized (38.2%). The compact morphotype was characterized by a high proportion of collagen (89.32±1.52%), minimal content of peritenonium (8.86±1.15%), and the highest compactness coefficient 0.91±0.01. In contrast, the disorganized morphotype demonstrated the lowest proportion of collagen (68.18±4.04%), the highest content of peritenonium (26.87±4.11%), a low compactness coefficient 0.72±0.05, widening of interfascicular spaces, remodeling of the vascular component, and signs of pronounced histostructural reorganization. The transitional morphotype occupied an intermediate position. All intercluster differences were statistically significant (p < 0.001).

Conclusions. Morphometric and cluster analysis of the external oblique aponeurosis revealed substantial structural variability and enabled the identification of three morphotypes–compact, transitional, and disorganized–which differed in the proportions of collagen fibers, peritenonium, vascular component, and compactness parameters. The identified morphological heterogeneity of the aponeurosis reflects different degrees of structural remodeling and may represent one of the factors contributing to variability in the outcomes of surgical correction of the anterior abdominal wall, thereby supporting the rationale for further individualization of surgical strategy.