Three-dimensional technology for linear morphological studies: a re-examination of cranial variation in four southern African indigenous populations

Statistical Shape Analysis of Subthalamic Nucleus in Patients with Parkinson Disease

OBJECTIVE

Subthalamic nucleus (STN) is the most targeted localization in the treatment of Parkinson disease (PD) with deep brain stimulation. However, no studies have been found in the literature about possible shape changes of STN in the literature. We aimed to investigate possible shape changes in the STN and the relationship between shape changes and disease duration in PD patients by using statistical analysis.

METHODS

Patients who were diagnosed with idiopathic PD and controls were enrolled in this study. Age, sex, and disease duration of all cases were recorded. Turbo-spin-echo T2-weighted axial series parallel to the skull base in each case containing midbrain images were obtained, including the whole STN. Standard anatomic landmarks were selected and marked on each digital image using a special software in all cases. Statistical geometric shape and deformation analysis of STN was performed in 2 groups.

RESULTS

Forty-three patients with PD and 50 age/sex-matched controls were enrolled in this study. There were statistically significant left and right STN shape differences between the groups. Maximum deformation was seen in the dorsolateral parts of both STNs. General shape variability of the STNs was found on the left (0.096) and right (0.049).

CONCLUSIONS

Significant shape differences and remarkable deformation of STN are seen in patients with PD compared with controls. Maximum deformation was observed in the dorsolateral part of the STN, and with the increase in the duration of the PD, shape differences and deformations became more prominent.

Three-dimensionally derived interlandmark distances for sex estimation in intact and fragmentary crania

The skull is the element most frequently presented to forensic anthropologists for analysis yet weathering, corpse maiming, and scavenger activity often result in damage and fragmentation. This fragmentation results in a reduction in the number of traditional calliper derived measurements that can be obtained and subjected to discriminant based analyses for sex estimation. In this investigation, we employed three-dimensional geometric morphometric methods to derive novel interlandmark distance measures across six regions of the cranium including the basicranium, basipalate, zygoma, orbits and the cranium globally to create functions to discriminate sex with high efficacy, even in the event of fragmentation. Forty-five homologous landmarks were digitised across each of 227 (114 males and 113 females) South African crania of European descent (white) sampled from the Raymond A Dart Collection of Human Skeletons, housed in the School of Anatomical Sciences, University of the Witwatersrand, South Africa. A total of 990 interlandmark distances (ILDs) were mathematically derived using Pythagorean geometry. These ILDs were then filtered by region and subjected to both direct and stepwise discriminant function analyses. Discriminant equations where derived for each region and achieved the following average cross-validated sex estimation accuracies: basicranium-74%; basipalate-80.2%; zygomatic-82.4; orbits-71.8%; nasomaxilla-83.7%; global cranium-88.2%. A large number of the ILDs used to derive the discriminant functions are novel, demonstrating the efficacy of geometric morphometric methods and illustrating the need to reassess old methods of data collection using modern methods to determine whether they best capture biological differences. The results of this study provide an invaluable contribution to forensic anthropology in South Africa as it provides an accurate, practical means of assessing sex using fragmentary material that may otherwise have been disregarded. These will undeniable aid in accurate sex estimation and ultimately, victim identification.

Revisiting historical Khoe-San skeletal remains in European collections: A search for identity through craniometric analysis

As the identity of a large number of Khoe-San skeletal material in European collections recently came into question during its documentation, a re-evaluation of the remains by employing a non-invasive method such as craniometrics was done to investigate the biological affinity. For this purpose, gene flow and population diversity present within the group, as well as between the study sample (N=63) and other modern and historic population groups from southern, central and east Africa were explored. Available comparative groups included the historic Khoe-San from Riet River (N=31), the Sotho-Tswana from southern Africa (N=61), the Basuku from central Africa (N=66) and the Bahutu (N=53) and Teita (N=24) from east Africa. Ten craniometric variables were selected and used to perform population structure analysis based on model bound quantitative genetics and multiple discriminant function analysis (MDA). Quantitative genetic distances revealed that the Khoe-San sample was closest to the Riet River group. Residual variance analysis performed on two-sample subsets of the Khoe-San group (Cape KS and Various KS) showed a higher level of heterogeneity in the Cape KS than seen in the Khoe-San from various other areas in southern Africa. MDA revealed that Khoe-San intra-sample variance is relatively high, with 44% of the sample (sexes pooled) classified into the Riet River group. The remaining individuals were classified (in decreasing order) into Bahutu (24%), Basuku (24%) and Sotho-Tswana (8%). Although the Khoe-San specimens are closest to the Riet River group, they are clearly not homogenous. Their high level of phenotypic diversity most likely originated from a complex population history involving many group interactions driven by social and political marginalization.

Study of sexual dimorphism of Malaysian crania: an important step in identification of the skeletal remains

Sex determination is one of the main steps in the identification of human skeletal remains. It constitutes an initial step in personal identification from the skeletal remains. The aim of the present study was to provide the population-specific sex discriminating osteometric standards to aid human identification. The present study was conducted on 87 (174 sides) slices of crania using postmortem computed tomography in 45 males and 42 females, aged between 18 and 75 years. About 22 parameters of crania were measured using Osirix software 3-D Volume Rendering. Results showed that all parameters were significantly higher in males than in females except for orbital height of the left eye by independent t test (P<0.01). By discriminant analysis, the classification accuracy was 85.1%, and by regression, the classification accuracy ranged from 78.2% to 86.2%. In conclusion, cranium can be used to distinguish between males and females in the Malaysian population. The results of the present study can be used as a forensic tool for identification of unknown crania.

A Non-Destructive Method for Distinguishing Reindeer Antler (Rangifer tarandus) from Red Deer Antler (Cervus elaphus) Using X-Ray Micro-Tomography Coupled with SVM Classifiers

Over the last decade, biomedical 3D-imaging tools have gained widespread use in the analysis of prehistoric bone artefacts. While initial attempts to characterise the major categories used in osseous industry (i.e. bone, antler, and dentine/ivory) have been successful, the taxonomic determination of prehistoric artefacts remains to be investigated. The distinction between reindeer and red deer antler can be challenging, particularly in cases of anthropic and/or taphonomic modifications. In addition to the range of destructive physicochemical identification methods available (mass spectrometry, isotopic ratio, and DNA analysis), X-ray micro-tomography (micro-CT) provides convincing non-destructive 3D images and analyses. This paper presents the experimental protocol (sample scans, image processing, and statistical analysis) we have developed in order to identify modern and archaeological antler collections (from Isturitz, France). This original method is based on bone microstructure analysis combined with advanced statistical support vector machine (SVM) classifiers. A combination of six microarchitecture biomarkers (bone volume fraction, trabecular number, trabecular separation, trabecular thickness, trabecular bone pattern factor, and structure model index) were screened using micro-CT in order to characterise internal alveolar structure. Overall, reindeer alveoli presented a tighter mesh than red deer alveoli, and statistical analysis allowed us to distinguish archaeological antler by species with an accuracy of 96%, regardless of anatomical location on the antler. In conclusion, micro-CT combined with SVM classifiers proves to be a promising additional non-destructive method for antler identification, suitable for archaeological artefacts whose degree of human modification and cultural heritage or scientific value has previously made it impossible (tools, ornaments, etc.).

Sexual dimorphism and population variation in the adult mandible : Forensic applications of geometric morphometrics

This article forms part of an ongoing series of investigations designed to apply three-dimensional (3D) technology to problems in forensic anthropology. We report here on new morphometric data examining sexual dimorphism and population variation in the adult human mandible. The material is sourced from dissection hall subjects of South African and American origin consequently the sex and a statement of age are known for each individual. Thirty-eight bilateral 3D landmarks were designed and acquired using a Microscribe G2X portable digitizer. The shape analysis software morphologika (www.york.ac.uk/res/fme) is used to analyze the 3D coordinates of the landmarks. A selection of multivariate statistics is applied to visualize the pattern, and assess the significance of, shape variation between the sexes and populations. The determination of sex and identification of population affinity are two important aspects of forensic investigation. Our results indicate that the adult mandible can be used to identify both sex and population affinity with increased sensitivity and objectivity compared to standard analytical techniques.

Statistical sex determination from craniometrics: Comparison of linear discriminant analysis, logistic regression, and support vector machines

Accuracy of identification tools in forensic anthropology primarily rely upon the variations inherent in the data upon which they are built. Sex determination methods based on craniometrics are widely used and known to be specific to several factors (e.g. sample distribution, population, age, secular trends, measurement technique, etc.). The goal of this study is to discuss the potential variations linked to the statistical treatment of the data. Traditional craniometrics of four samples extracted from documented osteological collections (from Portugal, France, the U.S.A., and Thailand) were used to test three different classification methods: linear discriminant analysis (LDA), logistic regression (LR), and support vector machines (SVM). The Portuguese sample was set as a training model on which the other samples were applied in order to assess the validity and reliability of the different models. The tests were performed using different parameters: some included the selection of the best predictors; some included a strict decision threshold (sex assessed only if the related posterior probability was high, including the notion of indeterminate result); and some used an unbalanced sex-ratio. Results indicated that LR tends to perform slightly better than the other techniques and offers a better selection of predictors. Also, the use of a decision threshold (i.e. p>0.95) is essential to ensure an acceptable reliability of sex determination methods based on craniometrics. Although the Portuguese, French, and American samples share a similar sexual dimorphism, application of Western models on the Thai sample (that displayed a lower degree of dimorphism) was unsuccessful.

Evaluation of discriminant functions for sexing skulls from visually assessed traits applied in the Rainer Osteological Collection (Bucharest, Romania)

The sexing of human skeletal remains based on visual scoring of descriptive traits on the skull is useful for both forensic and bioarchaeological studies, given that many such features preserve well in the field and can be assessed quickly. The goal of our work is to evaluate the accuracy of this method on an age-balanced, known sex, random sample of 360 modern adult crania in the Rainer Osteological Collection. Consistent with Walker (2008), we scored glabella area (G), the mastoid process (Ma), the mental eminence (M), the orbital edge (O) and the nuchal crest (N), on a five-point scale. We generated sex discriminant functions (logistic), selected the most accurate of them, and subsequently applied them to archaeological samples from Romania. Each skull feature showed significant score differences by sex. Eight out of 31 discriminant functions passed criteria of high accuracy (∼90%), sex bias (±2%), and ease of use (direct calculation of sex). The best estimates were obtained for the 30-60 age groups. Further testing these functions on six archaeological samples showed high percentages of agreement with the sex assessed on the coxal bone. The study also indicated that, although easy to learn by novices, the method of visually scoring the skull traits depends on prior experience with human osteology. The accuracy of the method may be influenced by geographical and historical differences which are bound to exist between populations.

Test of age-related variation in the craniometry of the adult human foramen magnum region: implications for sex determination methods

Sex differences in the foramen magnum region of the cranial base have been identified with varying rates of success. Recent publications demonstrate a continuing strong interest in metric analysis of the foramen magnum region for sex determination despite the generally low expression of cranial base sexual dimorphism. It is important to identify possible age effects on skull base morphometric variables as most reported discriminant analyses use pooled-age samples without assessing the influence of aging on sexual dimorphism. This study examined 135 adult cranial bases (69 males and 66 females) from the St. Bride's documented skeletal collection in London. Traditional craniometric measurements were recorded and the effect of age on sexual dimorphism of this anatomical region was tested using a variety of statistical analyses including MANOVA and discriminant function analysis. Age-dependent discriminant functions for <50 and >50 years of age were developed and compared. The cross-validated results showed that the <50 years function determined the sex of 69.1% correctly while the >50 years function achieved 81.3% correct predictions. However, the high sex biases of these functions (14.4% and -17.5%) severely limit their practical application. A pooled-age discriminant function permitted 71.9% correct prediction with a sex bias of only -1.7%. The statistical analyses also showed no significant age effect on any of the variables, suggesting that a separation by age is not necessary for the development of sex determination methods.

Quantification of the subpubic angle in South Africans

Due to the high crime rate in South Africa, forensic anthropologists are increasingly approached to aid in the identification of skeletonized remains, with sex and population affinity assignment being some of the most critical tasks they face. For over a century, the pelvis has been known to be one of the most sexually dimorphic bones of the human body and the subpubic angle is one of the most accurate, albeit scarcely quantified, features thereof. Hence, the aim of this study was to quantify the size of the subpubic angle and compare it between male and female South Africans of African (black) and European (white) descent. One hundred and forty five (145) pelves were selected, consisting of 68 white (43 male and 25 female) and 77 black South Africans (44 male and 33 female), from the Raymond A. Dart Collection of Human Skeletons housed at the University of the Witwatersrand, Johannesburg, South Africa. Each of the pelves were articulated and placed into a custom built stand for photographing. Measures of the subpubic angle from these digital images were subjected to numerous statistical analyses. Results indicated that significant differences exist between the sexes, as well as between the two population groups. For black individuals it was found that males generally possessed a subpubic angle of 74.9° or less, with larger values being indicative of the female sex. For white individuals, subpubic angles of 81.4° and less indicated males whilst larger values indicated females, with an average accuracy of 86% for both population groups. These results illustrate the advantages of using the subpubic angle to assist in the estimation of sex and population affinity and also reinforce the need for population specific parameters to be applied.

Mandibular Morphology as an Indicator of Human Subadult Age: Interlandmark Approaches

The dentition is widely recognized as the set of developmental markers that appear to show the least variability against chronological age; these markers are thus widely used in forensic anthropological investigations. As a possible alternative, we investigate here the potential of mandibular morphology as a developmental marker for estimating age at death in subadults. The sample analyzed comprises 79 known age and sex subadult individuals of South African Bantu and African American origin. Linear measurements of ramus height were obtained from the mathematical conversion of three-dimensional landmark data. A series of regression analyses were then performed to predict age by using the measurement of ramus height; results were cross-validated using a jackknife procedure. Our results show that ramus height can be used to predict age in the subadult skeleton with accuracy, closely approaching that of standards based on the dentition (standard error rates are between +/-1.1 years and +/-2.4 years).

Geometric morphometric study of population variation in indigenous southern African crania

Much of our understanding of population variation in southern Africa is derived from traditional morphometric research. In the search for new perspectives, this paper reports on new geometric morphometric data examining cranial variation in 12 modern human populations from southern Africa. In total, 298 male Bantu-speaking individuals were studied. In addition, a small Khoisan (Khoikhoi and San) series was also examined. The purpose of this study was to investigate Khoisan-Bantu morphological similarities and differences, and to examine variation within both the Bantu-speaking and Khoisan populations. The three-dimensional coordinates of 96 landmarks were analyzed, using the shape-analysis software morphologika. Interpopulation variation was examined by calculating Procrustes distances between groups; a cluster analysis was then used to summarize phenetic relationships. A principal components analysis explored the relationships between populations; shape differences were visualized and explored using three-dimensional rendered models, and further interpreted using thin-plate splines. Morphological differences are present within and between the crania of Bantu-speaking and Khoisan individuals. The Khoisan demonstrate features (e.g., a pentagonoid vault, more rounded forehead contour, and a small and less prognathic face) that clearly distinguish them from Bantu-speaking populations. Although southern African Bantu-speaking populations are clearly closely related, they show population-specific features (e.g., the crania of more southerly populations (Xhosa, Southern Sotho, and Zulu) are characteristically more brachycephalic and less prognathic). This study suggests that differential admixture with adjacent Khoisan peoples has contributed to diversity within southern African Bantu-speaking populations.