Sex and age related non-metric variation of the human sternum in a Northwest Indian postmortem sample: A pilot study

Abstract

Nonmetric traits are quasi-continuous skeletal traits that cannot be measured, but are observed as ranks or scores. In the present study, 8 nonmetric traits of sternum were examined from 343 sternums collected from the autopsy cases. More males, particularly older subjects, had a mesosternal foramen. The frequency of mesosternal foramen, arch-shaped prominence on the manubrium and radial strips on mesosternum significantly increased but that of lateral projection of manubrium decreased in the 30+ year age-group (older individuals). The denticulate costal incisures were found mostly in females and younger subjects; however, the crescent incisures and arch shaped prominence of manubrium were noticed mainly in males and older subjects. Majority of subjects had ‘deep and narrow’ jugular notch and xiphi-sternum was ‘bifid’ or ‘oblong’ in males and ‘small sized’ in females and younger subjects. Xiphi-sternum was generally found absent in females and younger subjects. The different shapes of costal incisures, jugular notch and xiphoid process were found to have significant sex and age differences. The number of cases with fused elements significantly increased with advancing age in both sexes. The sternal elements’ fusion showed a variable pattern and hence was not found to be a reliable criterion. Chi-square analysis revealed significant differences between two age-groups of individual sex in the distribution of 3 of the 8 nonmetric traits. Significant sex and age differences were noticed in the frequency of occurrence of mesosternal foramina between the younger and older age groups in both the sexes. The logistic regression analysis of the scores classified 73.8% sternums to their sex category and 70.0% sternums to their age-group. Though present findings may not be enough for absolute personal identification, these traits can still serve as important identification tools if antemortem radiographs/CT or MRI scans are available for comparisons, or help classify an unknown sternum to its sex or age category based on the morphological features discussed in present study.

Introduction

Proper identification of an individual is important not only for the family or friends of the deceased and is also necessary for proper completion of a variety of documents and for the purpose of settling insurance claims, estate issues, etc., by the law enforcement agencies. Means of identifying an individual are varied and depend upon the circumstances of each particular case. Also, the techniques and standards for identification may vary. The range of human variation is exceedingly broad and also includes bony variants (including nonmetric particulars) that if not properly assessed and interpreted, may be mistaken for fractures or other injuries [1], [2]. Human skeleton has subtle variations in its both metric and nonmetric features, thus, evaluation of these skeletal variants is essential for proper identification and individualization of skeletal remains encountered in forensic or bio-archaeological contexts. Metric analyses of complete skeletal parts have proved very fruitful in this effort; however, the availability of a complete skeleton/bone in such situations can never be guaranteed. The incomplete, fragmented/damaged or dismembered skeletal parts/bones (though still with some valuable information) pose a great challenge in identification of unknown remains.

Though discriminant function analysis is extremely useful for establishing identity of fragmentary remains using measurements of bone dimensions [3], [4], such estimates are highly population-specific and are not reproducible in other groups [5], [6], [7]. DNA identification of fragmentary skeletal remains is an option but molecular methods are rarely chosen at the cost of morphological method, especially in adult skeletons, because there are certain qualitative difficulties working with molecular methods like contamination with DNA of the investigator, inter-contamination between skeletal remains and corpses found in same graves, insufficient volume of DNA, certain new mutations while comparing with living relatives, etc. [8]. Both metric as well as non-metric analyses are prone to some inter-observer errors which depend largely upon the clarity of trait descriptions. The non-metric analysis of skeletal traits is quick to perform, requiring no sophisticated tools/techniques, when compared with the traditional morphometric analyses [9], [10], [11].

Chambellan [12] was, perhaps, the first to suggest the possibility of using such traits as anthropological characters. Hooton [13] remarked “morphological features which can be observed and described but cannot be measured, are probably of greater anthropological significance than diameters and indices” [14]. A number of nonmetric skeletal variants of the mammalian/human skeleton have been widely used in physical anthropology particularly to determine biological distances (variations) among populations [15], [16] genetic diversities [17], [18], race [9], [19], sex [20], age [21], [22] as well as activity/occupational stress markers of the skeleton [23]. Besides genetical and environmental factors, sex, age and, perhaps, weight of skeleton are the other factors taken to be responsible for their varied expression and they have significant importance in identification of skeletal remains that are too fragmentary to identify [24], [25].

Though cranial epigenic traits have been widely used as a tool for studying genetic variability, as taxonomic indicators and for purposes of identification [26], [27], [28], however, nonmetric traits of the infra-cranial skeleton have also been utilized for the purpose, though with greater limitations [29]. Since 1967 [30], a number of anthropological studies have been conducted for investigating side and sex dimorphism, age dependency, genetic or environmental control, etc., of discrete traits of human skeleton and also for determining any population distances and biological affinities of contemporary or archaeological populations [31]. Some researchers have found no age or sex dependency of these skeletal variants [29], [32] while others have found such correlations of utmost value in forensic sciences [29], [33], [34], [35]. The sternum bone is one such human skeletal element that has been rarely examined for its nonmetric traits and their relation to sex and age of the subjects except a few studies on frequency distribution of mesosternal foramen and age estimation from ‘patterns and sequences’ of fusion of three sternal segments [36], [37], [38], [39], [40], [41], [42], [43], [44], [45].