The mastoid triangle (Ma-Ast-Po) as a sexually dimorphic feature - a systematic review of 1604 human skulls and meta-analysis.

The mastoid triangle is the area between the craniometric landmarks Mastoidale (Ma), Asterion (Ast) and Porion (Po), which has been studied in the field of physical anthropology as an alleged tool for sexual dimorphism. The evidence in the current scientific literature, however, is disputable. This systematic review aimed to find out how safe is the mastoid triangle for sexual dimorphism. A research protocol submitted to PROSPERO (CRD42023488216) was designed based on PRISMA-P. Pubmed, SciELO, LiLACS, LIVIVO, Open Gray and Open Access Theses and Dissertations were searched with structured strategies. The Joanna Briggs Institute manual was followed and the critical appraisal checklist for cross-sectional studies was used. The search found 14 eligible studies out of 2148 initially screened. The combined sample consisted of 1604 human skulls. Eight studies (57,14%) clearly encouraged the use of the mastoid triangle for sexual dimorphism, while three (21,42%) advised against it. All the studies had a low risk of bias (75-100%). The standardized mean difference between male and females was between 1.00 and 1.42 without statistically significant differences between geographic regions (p > 0.05). Expressive heterogeneity and large confidence intervals were detected, showing great variability across studies. A country-specific subgroup meta-analysis revealed lack of statistically significant differences based on geographic regions. This systematic review showed low level of evidence to support the use of the mastoid triangle as a tool for sexual dimorphism.