Oval in males and triangular in females? A quantitative evaluation of sexual dimorphism in the human obturator foramen

Abstract

Among the numerous pelvic traits presenting sex differences, the obturator foramen is classically described as being oval in males and triangular in females. However, no demonstrations or detailed studies seem available in the literature. The purpose of this work was to study quantitatively this trait using Fourier analysis, because this methodological approach is particularly well adapted for discrimination between different simple shapes. Using this approach, an outline can be characterized by a series of harmonics (1 to n), each defined by two Fourier descriptors: amplitude (C(n)), describing the relative importance of the harmonic contribution to the original shape, and phase (Phi(n)), representing the orientation of the harmonic contribution. The material consisted of 104 three-dimensional CT reconstructions of adult pelves (52 males and 52 females). After size normalization, the outlines of the 104 left obturator foramens were studied. Significant differences were demonstrated with, in total, 84.6% of individuals presenting a correct inferred sex. The most discriminating descriptors were the phase of the second harmonic (C(2),) related to the oval (or elliptic) aspect and thus the elongation of the shape, and the amplitude of the third harmonic (Phi(3)), describing the triangularity of the shape. Because the trend for an outline to be more or less oval or triangular is difficult to visually assess and because there is an infinite number of transitional shapes, only a precise quantitative approach such as Fourier analysis allows for unambiguous characterization and statistical analysis.

Revisiting the Phenice technique sex classification results reported by MacLaughlin and Bruce (1990)

“…They also suggested that the experience of the observer was important, noting differences in accuracy of up to 14% between experienced and inexperienced observers. The article is cited by numerous forensic and bioarchaeological studies, including widely cited laboratory and field manuals, as indicative evidence that the accuracy of the Phenice method is variable depending on sample ancestry and the experience of the observer (e.g., Sutherland and Suchey, ; Tague, ; Rogers and Saunders, ; Lou, ; Cox and Mays, ; Bruzek, ; Scheuer, ; Ubelaker and Volk, ; Albanese et al, ; Listi and Bassett, ; Albanese et al, ; Cardoso and Saunders, ; Gonzalez et al, ; Bierry et al, ; Bytheway and Ross, ; White et al, ).…”

Evaluation of Obturator Foramen Suggests No Differences Between Sexes in Young Bovines

“…Thirdly, although FSA is a methodological approach particularly well adapted to discrimination between different simple shapes (Bierry et al., ), it too showed a low rate of accuracy in classification according to sex.…”

“…Fourier shape analysis (FSA) is a technique for generating from a poor outline, a set of shape‐representative variables suitable for use in statistical comparisons between samples. It has been applied to many bones, but there are few papers dealing with foramen analysis (Bierry et al., ).…”

“…The anatomical morphology of bone is used as an important tool for archaeologists to identify animal species, as well as to distinguish human from animals (Sajjarengpong et al., ). Several specific bones can be also used for determining the sex of animals, one being the pelvic bones (Sajjarengpong et al., ; Bierry et al., ). The pelvis is considered to be a part of the skeleton, which presents a large sexual dimorphism (De Panafieu, ).…”

“…The pelvis is considered to be a part of the skeleton, which presents a large sexual dimorphism (De Panafieu, ). Many parts of the human pelvic bones have been studied, such as the great sciatic notch (Jovanovic and Zivanovic, ; Jovanovic et al., ; Singh and Potturi, ; Hager, ), the cranial border (Gomez and Fernãndez, ), the obturator foramen (Bierry et al., ) and the entire bone (Milne, ). Pelvic studies have been also carried out in non‐human anthropoids (Gingerich, ; Hager, ) and also in species such as the dog (Sajjarengpong et al., ), grey foxes (Schutz et al., ), the northern water vole (Ventura et al., ), the mouse (Uesugi et al., ,b, ), whales (Bejder and Hall, ) and the bat (Nwoha, ), but no detailed studies of bovine obturator foramen are available in the veterinary literature.…”