Sex Determination from the Second Cervical Vertebra: A Test of Wescott’s Method on a Modern American Sample*

Sex Determination via the Second Cervical Vertebra and Odontoid Process: A Case Report and a Review of the Literature

Determining an individual's sex is crucial in several fields, such as forensic anthropology, archaeology, and medicine. Accurate sex estimation, alongside the estimation of age at death, stature, and ancestry, is of paramount importance for creating a biological profile. This profile helps narrow the potential pool of missing persons and aids identification. Our research focuses on the second cervical vertebra and odontoid process, which is particularly valuable due to their high sexual dimorphism. This brief research is structured as follows: we provide an overview of morphometric analysis of the second cervical vertebra for accurate sex estimation in forensic anthropology. We then delve into a case report to explore sexual dimorphism of the C2 vertebrae. Moreover, we discuss some of these studies that showed a significant correlation between the dimensions of the second cervical vertebrae and height, suggesting that the C2 can be used as a reliable indicator for stature estimation. The high accuracy rate of sex estimation using the second cervical vertebrae suggests that this method is a valuable tool for forensic anthropologists. Its practical application can significantly contribute to identifying and profiling individuals in a forensic context, thereby aiding in the identification process.

Sexual dimorphism of the twelfth thoracic vertebra for sex determination in the Central Thai population

Analyzing skeletal remains is crucial for identifying individuals, and forensic anthropologists use this analysis to determine biological characteristics, particularly sex, aiding criminal investigations. Among thoracic vertebrae, the twelfth thoracic vertebra (T12) is highly sexually dimorphic in various populations. This study aims to establish a discriminant function equation (DFE) for sex determination based on T12 in the Central Thai population. A total of 15 parameters of T12 were examined in 69 bone samples (43 males and 26 females). Among the 15 parameters, 14 were significantly different between males and females. The discriminant function equation (DFE) was generated as DFE = -19.578 + 0.376(i) BDsm + 0.254(l) PW + 0.081TDm, with a cutoff value of -0.296 for males and females, showing 92.8 % accuracy. The evaluation of the DFE using 10 blind samples showed 90 % accuracy. These findings may offer an additional method for sex determination through T12, complementing the examination of other skeletal elements.

Sex estimation using the human vertebra: a systematic review

Background

The vertebral column has been used in forensic studies for its weight-bearing function and relative density. Sex estimation is one of the essential elements in an anthropological examination, as it may narrow down the possibility of a match by half. Hence, it is crucial to derive the population-specific reference data in each vertebra for sex estimation. This systematic review explored the most sexually dimorphic vertebra by using the conventional anthropometric analysis.

Main body

An electronic comprehensive search was conducted using databases such as Scopus, Web of Science (WOS) and EBSCO Medline for relevant studies between 2008 and 2020. The main inclusion criteria were studies in English, and studies on sex estimation by morphometric analysis of vertebra by CT scan or dry bone. Only studies related to human adult age and vertebra were analysed. Literature search identified 84 potentially relevant articles, in which 19 articles had fulfilled the inclusion criteria. This review included studies on the cervical, thoracic and lumbar vertebrae in different populations.

Conclusion

The vertebral spine has demonstrated significant sexual dimorphism with variable prediction accuracies, whereby the body of a vertebra was found to be sexually dimorphic. It was shown that high accuracy of sex classification was provided by the second cervical, twelfth thoracic and first lumbar vertebrae, especially when they were used in combination.

Contributions of anatomy to forensic sex estimation: focus on head and neck bones

This study sought to provide an up-to-date review of the importance of anatomy to human identification, focusing on the usefulness of anatomical knowledge about the head and neck bones and teeth to sex estimation in routine forensic anthropology methods. A detailed search of osteology applications in forensic sex estimation was conducted through the electronic databases for the 10 years prior to July 2020. Relevant articles and classic literature on the subject were gathered and are outlined in this review. Among the available literature, several metric analyses showed accuracy superior to 80% in sexual diagnosis. Angles measured from the inclination of glabellae and analysis of the external frontal bone surface through three-dimensional computer-aided design emerge as reliable cranial indexes for sex estimation. In the mandible, the condylar and coronoid height, bigonial width, and coronion–gonion distance express significant sexual dimorphism. Measurements of the canine are the best option for sex estimation using teeth, as well as the thickness of the dentine or enamel of incisors. The axis vertebra surpasses other neck bones for sex estimation due to its atypical shape and the presence of the odontoid process. Metric analyses based on anatomy can provide reliable accuracy in sexual diagnosis. Adequate training and anatomical knowledge can reduce bias and interobserver differences, and the use of three-dimensional models and computed tomography images can enhance the accuracy of these methods for sex estimation. However, every method should be validated before being applied to a different population.

Key Points

• Anatomy-based metric analyses can provide reliable accuracy in forensic sex estimation.

• Glabellae inclination, external frontal bone surface, mandible, and canine teeth measurements can reach accuracies superior to 80% in sexual diagnosis.

• The use of three-dimensional models and computed tomography images can enhance accuracy in sex estimation.

• Every method should be validated before being applied to a different population.

A hierarchy of expert performance as applied to forensic anthropology

Due to their medicolegal repercussions, forensic anthropology conclusions must be reliable, consistent, and minimally compromised by bias. Yet, a synthetic analysis of the reliability and biasability of the discipline's methods has not yet been conducted. To do so, this study utilized Dror's (2016) hierarchy of expert performance (HEP), an eight-level model aimed at examining intra- and inter-expert reliability and biasability (the potential for cognitive bias) within the literature of forensic science disciplines. A systematic review of the forensic anthropology literature was conducted (1972-present), including papers published in the American Journal of Physical Anthropology, Forensic Anthropology, Forensic Science International, and the Journal of Forensic Sciences and Anthropology Section abstracts published in the Proceedings of the Annual Meeting of the AAFS which matched keywords such as "forensic anthropology," "bias," "reliability," "cognition," "cognitive," or "error." The resulting forensic anthropology HEP showcases areas that have ample research and areas where more research can be conducted. Specifically, statistically significant increases in reliability (p < 0.001) and biasability (p < 0.001) publications were found since 2009 (publication of the NAS report). Extensive research examined the reliability of forensic anthropological observations and conclusions (n = 744 publications). However, minimal research investigated the biasability of forensic anthropological observations and conclusions (n = 20 publications). Notably, while several studies demonstrated the biasing effect of extraneous information on anthropological morphological assessments, there was no research into these effects on anthropological metric assessments. The findings revealed by the forensic anthropology HEP can help to guide future research, ultimately informing the development and refinement of best-practice standards for the discipline.

Virtual morphometric method using seven cervical vertebrae for sex estimation on the Turkish population

Sex estimation from skeletal remains is crucial for the estimation of the biological profile of an individual. Although the most commonly used bones for means of sex estimation are the pelvis and the skull, research has shown that acceptable accuracy rates might be achieved by using other skeletal elements such as vertebrae. This study aims to contribute to the development of sex estimation standards from a Turkish population through the examination of CT scans from the seven cervical vertebrae. A total of 294 individuals were included in this study. The CT scans were obtained from patients attending the Bakirkoy Training and Research Hospital (Turkey) and the data was collected retrospectively by virtually taking measurements from each cervical vertebrae. The full database was divided into a training set (N = 210) and a validation set (N = 84) to test the fit of the models. Observer error was assessed through technical error of measurement and sex differences were explored using parametric and non-parametric approaches. Logistic regression was applied in order to explore different combinations of vertebral parameters. The results showed low intra- and inter-observer errors. All parameters presented statistically significant differences between the sexes and a total of 15 univariate and multivariate models were generated producing accuracies ranging from a minimum of 83.30% to a maximum of 91.40% for a model including three parameters collected from four vertebrae. This study presents a virtual method using cervical vertebrae for sex estimation on the Turkish population providing error rates comparable to other metric studies conducted on the postcranial skeleton. The presented results contribute not only to the development of population-specific standards but also to the generation of virtual methods that can be tested, validated, and further examined in future forensic cases.

Forensic sex estimation using the vertebrae: an evaluation on two European populations

Sex estimation is one of the primary steps for constructing the biological profile of skeletal remains leading to their identification in the forensic context. While the pelvis is the most sex diagnostic bone, the cranium and other post-cranial elements have been extensively studied. Earlier research has also focused on the vertebral column with varying results regarding its sex classification accuracy as well as the underlying population specificity. The present study focuses on three easily identifiable vertebrae, namely T1, T12, and L1, and utilizes two modern European populations, a Greek and a Danish, to evaluate their forensic utility in sex identification. To this end, 865 vertebrae from 339 individuals have been analyzed for sexual dimorphism by further evaluating the effects of age-at-death and population affinity on its expression. Our results show that T1 is the best sex diagnostic vertebra for both populations reaching cross-validated accuracy of almost 90%, while age-at-death has limited effect on its sexual dimorphism. On the contrary, T12 and L1 produced varying results ranging from 75 to 83% accuracy with the Greek population exhibiting distinctively more pronounced sexual dimorphism. Additionally, age-at-death had significant effect on sexual dimorphism of T12 and L1 and especially in the Greek female and Danish male groups. Our results on inter-population comparison suggest that vertebral sex discriminant functions, and especially those utilizing multiple measurements, are highly population specific and optimally suitable only for their targeted population. An open-source software tool to facilitate classifying new cases based on our results is made freely available to forensic researchers.

Morphometric research and sex estimation of lumbar vertebrae in a contemporary Spanish population

In the identification and reconstruction of the biological profile of skeletal remains in physical and forensic anthropology, sex estimation is a fundamental step, and is essential to achieve methods that allow the highest allocation accuracy. This study proposes a method to estimate the sex of skeletal remains using lumbar vertebrae. A total of 33 linear measurements for each lumbar vertebra were taken in 94 identified, contemporary, and adult skeletal remains (46 male and 48 female) from the cemetery of San José in Granada. The sexual dimorphism of each variable was analyzed, an intra- and interobserver error analysis was developed to assess the variables with best concordance, and the discriminant equations were obtained through a binary logistic regression analysis. All lumbar vertebrae show statistically significant sexual dimorphism with higher values in males than in females. Equations with an allocation accuracy of between 80% and 94.5% were obtained, showing that the lumbar vertebrae are a useful alternative for sex estimation when other skeletal elements are not well-preserved or available. The differences of biogeographic history between populations could translate into morphometric differences, which means that it is not advisable to use discriminant equations in a universal way. In spite of the high allocation accuracy of the equations developed, they should be applied in adults from populations similar to the present study to obtain reliable results of sexual estimation, until its validation in other populations.

Estimating sex from the seven cervical vertebrae: An analysis of two European skeletal populations

Methods for estimating sex from a variety of skeletal elements is vital in forensic anthropology as many of the traditionally studied bones are often fragmented upon recovery. The current study examined the seven cervical vertebrae to establish an accurate sex estimation method for Europeans. Discriminant functions were developed from the seven cervical vertebrae using the maximum body height (CHT), vertebral foramen anterior-posterior diameter (CAP), and vertebral foramen transverse diameter (CTR). To date, no study has used these variables to estimate sex from human remains. Two hundred and ninety-five adult individuals (157 males, 138 females) from the University of Athens and the Luis Lopes skeletal collections were studied. No population differences were exhibited between the contemporary Greek and historic Portuguese skeletons, indicating that discriminant functions for sex estimation from the cervical vertebrae may not be population- or temporally-specific. The results of this study indicate that only CHT and CTR exhibited statistically significant sexual dimorphism. Seven multivariate discriminant functions were developed with accuracy rates between 80.3% and 84.5%. Cross-validation studies showed that five of the seven functions exhibited strong statistical algorithms. This study will assist with estimating the sex of unknown Europeans from the cervical vertebrae especially in cases where more accurate predictors of sex, such as the skull or the pelvis, are unavailable.

Towards a new osteometric method for sexing ancient cremated human remains. Analysis of Late Bronze Age and Iron Age samples from Italy with gendered grave goods

Sex estimation of human remains is one of the most important research steps for physical anthropologists and archaeologists dealing with funerary contexts and trying to reconstruct the demographic structure of ancient societies. However, it is well known that in the case of cremations sex assessment might be complicated by the destructive/transformative effect of the fire on bones. Osteometric standards built on unburned human remains and contemporary cremated series are often inadequate for the analysis of ancient cremations, and frequently result in a significant number of misclassifications. This work is an attempt to overcome the scarcity of methods that could be applied to pre-proto-historic Italy and serve as methodological comparison for other European contexts. A set of 24 anatomical traits were measured on 124 Bronze Age and Iron Age cremated individuals with clearly engendered grave goods. Assuming gender largely correlated to sex, male and female distributions of each individual trait measured were compared to evaluate sexual dimorphism through inferential statistics and Chaktaborty and Majumder's index. The discriminatory power of each variable was evaluated by cross-validation tests. Eight variables yielded an accuracy equal to or greater than 80%. Four of these variables also show a similar degree of precision for both sexes. The most diagnostic measurements are from radius, patella, mandible, talus, femur, first metatarsal, lunate and humerus. Overall, the degree of sexual dimorphism and the reliability of estimates obtained from our series are similar to those of a modern cremated sample recorded by Gonçalves and collaborators. Nevertheless, mean values of the male and female distributions in our case study are lower, and the application of the cut-off point calculated from the modern sample to our ancient individuals produces a considerable number of misclassifications. This result confirms the need to build population-specific methods for sexing the cremated remains of ancient individuals.

Morphometric analysis of the humerus in an adult South African cadaveric sample

Recent studies using geometric morphometrics have shown that estimations of demographic parameters can be made using skeletal elements previously not thought useful for such purposes. This study used geometric morphometrics to assess humeral morphological variation in an adult South African sample, and evaluated the accuracy of sex and ancestry estimations based on this variation. Humeri of 1046 adult South African individuals (464 females, 582 males) were digitized. Data sets were rotated and scaled to a common centroid using Generalized Procrustes Analysis. Mean centroid sizes between groups were compared using parametric tests, while morphological variation was evaluated using multivariate analyses. Discriminant Function Analysis coupled with leave-one-out cross-validation tests were used to assess the reliability of sex and ancestry classifications based on this variation. Male humeri were relatively larger and presented with morphological features indicative of larger muscle mass and smaller carrying angles than females. White individuals had relatively larger but morphologically less robust humeri than Black or Coloured individuals, likely a reflection of both genetic and socio-economic differences between the groups as enforced under Apartheid law. When sex and ancestry were assessed together, similar variations were detected than when either parameter was individually assessed. Classification accuracy was relatively low when sex was independently assessed (73.3%), but increased when considered in conjunction with ancestry, indicating greater variation between-groups (ancestry) than within-groups. Ancestry estimation accuracies exceeded 80%, even for the highly diverse Coloured group. Classification accuracies of sex-ancestry groups all exceeded 76%. These results show that humerus morphological variation is present and may be used to estimate parameters, such as sex and ancestry, even in complex groups such as the Coloured sample of this study.

Sexual determination based on multidetector computed tomographic measurements of the second cervical vertebra in a contemporary Japanese population

Accurate sex estimation is important in forensic investigation to determine the identity of unknown individuals. The aim of this study was to investigate the accuracy of sex assessment based on measurements of the second cervical vertebra (C2) using computed tomographic (CT) images in a Japanese population and to develop discriminant function formulae. The data were collected from 224 Japanese cadavers (112 male subjects, 112 female subjects) on which postmortem CT scanning and subsequent forensic autopsy were performed. Nine CT measurements of the C2 were performed for CT images of each subject. The measurements were assessed using descriptive statistics and discriminant function analyses (DFA). All of the measurements demonstrated significant sexual dimorphism. Multiple DFA with stepwise variable selection resulted in multivariable models; a five-variable model reached an accuracy rate of 92.9%. Our results suggest that metric analysis based on CT images of the C2 can accurately determine the sex from the human skeletal remains in a contemporary Japanese population and may be useful for sex estimation in forensic anthropology.

Sex determination by discriminant function analysis of lumbar vertebrae

Sex determination is critical for developing the biological profile of unidentified skeletal remains. When more commonly used elements (os coxa, cranium) for sexing are not available, methods utilizing other skeletal elements are needed. This study aims to assess the degree of sexual dimorphism of the lumbar vertebrae and develop discriminant functions for sex determination from them, using a sample of South African blacks from the Raymond A. Dart Collection (47 males, 51 females). Eleven variables at each lumbar level were subjected to univariate and multivariate discriminant function analyses. Univariate equations produced classification rates ranging from 57.7% to 83.5%, with the highest accuracies associated with dimensions of the vertebral body. Multivariate stepwise analysis generated classification rates ranging from 75.9% to 88.7%. These results are comparable to other methods for sexing the skeleton and indicate that measures of the lumbar vertebrae can be used as an effective tool for sex determination.

Sex estimation using the second cervical vertebra: a morphometric analysis in a documented Portuguese skeletal sample

Biological sex estimation is one of the main parameters required in the construction of a biological profile of an unknown deceased person. In corpses in an advanced state of decomposition, skeletonized or severely mutilated, bone analysis may provide the only way to access biological sex. Although the hip bones are the most dimorphic and useful bones for sex estimation, they are often badly preserved and/or fragmented or may not even be present in some cases. For that reason, it is necessary to develop sex estimation methods based on bones less dimorphic. In this study, 13 dimensions of the second cervical vertebra were measured in order to quantify sex-related variation and to generate a simple predictive model based on logistic regression analysis. For logistic regression fitting, 190 individuals from the Coimbra Identified Skeletal Collection were used as a training sample. The resulting model was also evaluated in an independent test sample composed of 47 individuals from the Identified Skeletal Collection of the 21st Century (University of Coimbra). The developed logistic regression model correctly estimated known sex in 86.7 to 89.7 % of the cases. The second cervical vertebra demonstrated to be a useful alternative for sex estimation when other skeletal elements are not available or suitable for analysis. This method seems promising but more reliability studies are required for a more robust validation.