Pair-matching iliac bones: preliminary results from stereophotogrammetric analysis for sorting commingled remains

Sorting commingled human skeletal remains is among the most demanding assignments anthropologists are tasked with. Yet, it is of paramount importance to carry out the bio- logical profile and to start the personal identification proce- dures. Currently, the segregation of mixed bones into single individuals is performed by morphological and osteometric methods, which have been extensively used in the resolution of archaeological and forensic commingled settings. Nevertheless, these two approaches present several limita- tions related to the dimension and features of the assem- blage (e.g., number of involved individuals, homogeneity of the sample). Recent works suggested a three-dimensional approach for pair-matching homologous bones (i.e., right and left humeri, temporal bones, phalanges, clavicles), where 3D digital models of the bones are acquired and superimposed. Root Mean Square (RMS) values are then used as a proxy to discern matches and mismatches. This presentation will review the state of art about the 3D approach for pair-matching commingled bones and will describe the preliminary results on pair-matching iliac bones. For this pilot study, a sample of 10 male individuals was selected from the Collezione Antropologica LABANOF (CAL), a documented skeletal collection. The anterior sur- face of 20 innominate bones underwent image acquisition by stereophotogrammetry (Vectra-3D®) and was elaborated by VAM software® to isolate the ilium. A superimposition protocol was designed, and the 3D surfaces were superim- posed two at once in 10 matches and 50 mismatches. Finally, the RMS point-to-point distance of one model from the other one was calculated; this value was used to assess the performance of the method for sorting matches and mis- matches. The resulting data indicate that RMS values between matches and mismatches are significantly different (p<0.001) and that a given RMS threshold of 2.9 mm can discern the pairs of iliac bones with a sensitivity rate of 100% and a specificity rate of 60%. The results will be dis- cussed focusing on factors influencing the success rates, such as the postmortem damage. Although this approach is time-consuming, it provides a numerical value (i.e., RMS value) that indicates tentative matches and mismatches and could be employed as an effective screening test, followed by in-depth analyses. Further research will include increas- ing the accuracy of the results and testing the technique on unresolved commingled assemblages, such as the thousand skeletal remains of the sepulchre of the Ospedale Maggiore of Milan (Ca’ Granda) and those of the shipwreck that occurred on April 18, 2015.