Patella sex determination by 3D statistical shape models and nonlinear classifiers

Sex determination is one of the essential steps in personal identification of an individual from skeletal remains. Most elements of the skeleton have been subjected to discriminant function analysis for sex estimation, but little work has been done in terms of the patella. This paper proposes a new sex determination method from the patella using a novel automated feature extraction technique. A dataset of 228 patellae (95 females and 133 males) was amassed from the William M. Bass Donated Skeletal Collection from the University of Tennessee and was subjected to noninvasive high resolution computed tomography (CT). After the CT data were segmented, a set of features was automatically extracted, normalized, and ranked. The segmentation process with surface smoothing minimizes the noise from enthesophytes and ultimately allows our methods to distinguish variations in patellar morphology. These features include geometric features, moments, principal axes, and principal components. A feature vector of dimension 45 for each subject was then constructed. A set of statistical and supervised neural network classification methods were used to classify the sex of the patellar feature vectors. Nonlinear classifiers such as neural networks have been used in previous research to analyze several medical diagnosis problems, including quantitative tissue characterization and automated chromosome classification. In this paper, different classification methods were compared. Classification success ranged from 83.77% average classification rate using labels from a Fuzzy C-Means (FCM) clustering step, to 90.3% for linear discriminant classification (LDC). We obtained results of 96.02% and 93.51% training and testing classification rates, respectively, using feed-forward backpropagation neural networks (NN). These promising results using newly developed features and the application of nonlinear classifiers encourage the usage of these methods in forensic anthropology for identifying the sex of an individual from incomplete skeletons retaining at least one patella.     

Analysis of age-at-death estimation through the use of pubic symphyseal data

The question of whether age parameters derived from an American population will reliably estimate age-at-death for East European skeletal populations is important since the ability to accurately estimate an individual's age-at-death hinges on what standard is used. A reference sample of identified individuals with known ages-at-death from the regions of the Former Yugoslavia (n = 861) is used to determine the age structure of victims and serves as the prior in the Bayesian analysis. Pubic symphyseal data in the manners of Todd (Am J Phys Anthropol, 3 [1920], 285; Am J Phys Anthropol, 4 [1921], 1) and Suchey-Brooks (Am J Phys Anthropol, 80 [1986], 167) were collected for n = 296 Balkan males and females and for n = 2078 American males and females. An analysis of deviance is calculated using an improvement chi-square to test for population variation in the aging processes of American and East European populations using proportional odds probit regression. When males and females are treated separately, there is a significant association among females and the population (df = 1, chi-square likelihood ratio = 15.071, p = 0.001). New age estimates for Balkan populations are provided and are based on the calculated age distribution from the Gompertz-Makeham hazard analysis and the ages-of-transition. To estimate the age-at-death for an individual, the highest posterior density regions for each symphyseal phase are provided.     

Modification of the Trotter and Gleser female stature estimation formulae.

Stature-estimation formulae in common use are those of Trotter and Gleser. Their formulae for females are based on Terry collection skeletons. These skeletons are from people who died in the early 1990s. Because there has been considerable change in body size since then, it is possible that the Trotter and Gleser formulae are inappropriate for modern forensic-science application. The Trotter and Gleser female formulae are tested using data from the Forensic Data Bank at the University of Tennessee. For whites, the femur and tibia yield stature estimates differing from one another by about 3 cm. Using femur and tibia lengths from modern forensic cases and modern height data from anthropometric surveys, new regression intercepts are calculated for Trotter and Gleser's female formulae. The new intercepts improve the performance of the formulae on modern individuals. The Trotter and Gleser formulae for black females require no adjustment. Both blacks and whites have experienced a secular increase in bone length, but whites have experienced a change in proportions as well.     

Sexing and stature estimation criteria for Balkan populations

Abstract:  Two standard measurements, maximum femur length and head diameter, were collected by International Criminal Tribunal (ICTY) anthropologists. Only Kosovans had both femur dimensions for both sexes. Antemortem stature data were available only for Kosovan and Croatian males. Despite these limitations, the data offer the opportunity to examine ethnic variation and to present sex and stature estimation criteria for these groups. Additional data from Croatians and from American Whites were used for comparison in certain parts of the analysis. Femur variation was considerable. Kosovans can be characterized as short and robust, Bosnians as tall and less robust, and Croatians are tall and gracile, resembling American Whites more than the other groups. Some limited antemortem data on stature was also available, allowing stature estimation equations to be estimated for Croatians and Kosovans. Antemortem stature estimates were obtained from interviews with relatives and are shown to overestimate actual stature. We argue that equations predicting height obtained from relatives is the most realistic in this case because that is the height to which an estimate obtained from bone lengths will be compared. Kosovans were also shown to have experienced slight secular increase in femur length over the past 70 years.     

Investigation into Seasonal Scavenging Patterns of Raccoons on Human Decomposition,

Although raccoons are known as one of the most common scavengers in the U.S., scavenging by these animals has seldom been studied in terms of forensic significance. In this research, the seasonal pattern of raccoon scavenging and its effect on human decomposition was investigated using 178 human cadavers placed at the Anthropological Research Facility (ARF) of the University of Tennessee, Knoxville (UTK) between February 2011 and December 2013. The results reveal that (i) the frequency of scavenging increases during summer, (ii) scavenging occurs relatively immediately and lasts shorter in summer months, and (iii) scavenging influences the decomposition process by hollowing limbs and by disturbing insect activities, both of which eventually increases the chance of mummification on the affected body. This information is expected to help forensic investigators identify raccoon scavenging as well as make a more precise interpretation of the effect of raccoon scavenging on bodies at crime scenes.     

Improving Sex Estimation from Crania Using a Novel Three‐dimensional Quantitative Method,,

This study utilizes an innovative 3D approach to discover metric variables that obtain the highest classification rates for sex estimation from the cranium. Models were constructed from 222 cranial CT scans of U.S. Whites from the Bass Donated Collection. These models were used to create a statistical bone atlas that captures the primary shape variation in the skull and facilitates rapid computer‐automated analyses. The bone atlas showed that important size‐related sex variables are bizygomatic breadth, maximum cranial length, cranial base length, and mastoid height. Shape‐related variables capture sex differences in the projection of the glabellar region, inclination of the frontal, and cranial base flexion. In addition, vault thickness is highly dimorphic, with females having on average thicker vaults in the frontal region, and males having thicker vaults in the occipital region. Cross‐validated linear discriminant analysis obtained >95% accuracy (97.5% with 11 variables and 95.5% with eight variables).     

Measuring the Tibia: Trotter’s Error Revisited

In Trotter and Gleser’s (Am J Phys Anthropol 1952;10:463) classic study of stature estimation, a definition of the tibia length measurement is given that agrees with the standard condylar-malleolar length. That Trotter did not in fact measure according to her definition, but rather omitted the malleolus, has been well documented by Jantz et al. (J Forensic Sci 1995;40:758). Both the Terry collection and the World War 2 (WW2) samples were affected, although questions remain about the latter that cannot be resolved directly because it is no longer available for examination. Trotter's data from hundreds of servicemen are especially important because the statures were measured by technicians, rather than based on cadaver lengths or forensic statures. The questions examined in this note are as follows: Was WW2 measured uniformly in the same way as Terry; are there differences between Terry and WW2 that could influence estimation of the adjustment; and is the 10 millimeter (mm) adjustment proposed by Jantz et al. (J Forensic Sci 1995;40:758) still appropriate. Our analysis relies on a measurement taken by Trotter that is clearly and uniquely defined, what she called “ordinary length”. This measurement was used to create expectations about how Trotter measured what she called maximum length of the tibia. Results provide no evidence that WW2 was measured any differently than Terry, with the exception of one small series. They also show slight morphological differences on the distal and/or proximal end of the tibia between Terry and WW2. Despite the slight difference, the adjustment to account for the malleolus is still valid.     

Storm‐Related Postmortem Damage to Skeletal Remains

In April 2011, human skeletons were exposed to heavy storms at the outdoor Anthropology Research Facility (ARF) in Knoxville, Tennessee. Of the approximate 125 skeletons at the ARF in April 2011, 30 donations exhibited postmortem damage that could be attributed to the storms. At least 20 of the affected donations exhibit postmortem damage clearly associated with hailstones due to the oval shape and similar small size of the defects observed. The irregular shape and larger size of other defects may be a product of other falling objects (e.g., tree branches) associated with the storms. Storm‐related damage was observed throughout the skeleton, with the most commonly damaged skeletal elements being the scapula and ilium, but more robust elements (i.e., femora and tibiae) also displayed characteristic features of hailstone damage. Thus, hailstone damage should be considered when forensic practitioners observe unusual postmortem damage in skeletal remains recovered from the outdoor context.     

Spheno-occipital synchondrosis fusion in modern Americans

This study examines spheno-occipital synchondrosis fusion in the modern American population and presents age ranges for forensic use. The sample includes 162 modern individuals aged 5-25 years. The basilar synchondrosis was scored as open, closing, or closed via direct inspection of the ectocranial site of the suture. Transition analysis was used to determine the average ages at which an individual transitions from unfused to fusing and from fusing to fused. The maximum likelihood estimates from the transition analysis indicate that females are most likely to transition from open to closing at 11.4 years and males at 16.5 years. Females transition from closing to closed at 13.7 years and males at 17.4 years. The probability distributions associated with these maximum likelihood estimates were used to derive age ranges for age estimation purposes. These results reflect sexual dimorphism in basilar synchondrosis fusion and agree approximately with average age at pubertal onset.