Estimating Sex of Modern Greeks Based on the Foramen Magnum Region

3.1. Results

The results of the descriptive statistics are presented in Table 1. The mean values for all parameters were higher in males than females. All data were normally distributed according to the results of the Shapiro-Wilk test. Consequently, a parametric test was performed in order to ascertain whether any bilateral asymmetry exists regarding the dimensions of the occipital condyles and to analyze sex differences. According to Table 2, no statistically significant difference between right and left side was found in either the occipital condyle length or the occipital condyle breadth. Therefore, the averages of the distances obtained from both sides were used in the subsequent analysis.

The results shown in Table 3 indicate that, with the exception of the foramen magnum index, all parameters are influenced by sex (p < 0.05). The discriminant functions for each single parameter and five possible combinations of them are given in Table 4. Additionally, Table 4 shows the results of the cross-validation based on “leave-one-out” principle. The most reliable single parameter for sex determination was the occipital condyle length (69.5%) followed by Radinsky’s area (66.9%). Finally, the minimum intercondylar distance combined with the occipital condyle length as well as the occipital condyle breadth proved to be the best combination of parameters regarding sex determination (74.0%) followed by the combination of Radinsky’s area, the occipital condyle length, and the occipital condyle breadth (72.1%).

3.2. Discussion

Regarding the nonexistence of bilateral asymmetry of the occipital condyles, our results are in agreement with those of other populations [17, 18]. Additionally, the present study confirms the results of Natsis and his colleagues [15] regarding the presence of sexual dimorphism in the foramen magnum region in the modern Greek population. Natsis and his colleagues’ [15] sample included skulls of unknown age, mainly from the collection of the Departments of Anatomy of Aristotle University (Thessaloniki). On the other hand, all the individuals we examined were acquired from cemeteries in the Athens area with known age at death and year of birth. The mean values of length and width of the foramen magnum and the mean value of breadth of the occipital condyle of our sample are similar to Natsis and his colleagues sample. However, when comparing the mean values of the length of the occipital condyle and minimum intercondylar distance, our sample shows smaller and bigger values, respectively (Table 5). According to our observations, there might be variation in the occipital condyles among different parts of Greece.

Comparison of the distance parameters in different populations is given in Table 5. When observing the description of the foramen magnum length and the foramen magnum breadth, the modern Greek population seems to show similar values for males and females, as the Turkish [19, 20], British [11], and Spanish [21] populations. The Indian [22] population, especially the Indian females, seems to show smaller values, when compared to the aforementioned populations.

In regard to the occipital condyle variables, the Greek population has higher OCB value than the European American [23], the African American [23], the Turkish [20], and the British [24] populations. According to Uysal and her colleagues [20], the Turkish population demonstrates by far the lowest values of MID. The extreme values for MID in Uysal et al.’s [20] paper suggests an error in reporting or a typo in the final manuscript. Finally, according to our results, the Greek population has similar OCL value with the European American [23] and the British [24] populations.

In the Greek population, the best determination of the correct sex, regarding the foramen magnum variables, was achieved through the foramen magnum area (66.9%), while the combination of the foramen magnum variables achieved only 65.6% (Table 4). In comparison, the occipital condyles provide a higher determination of the correct sex than the foramen magnum. The combination of the occipital condyle variables allowed for the development of discriminant functions that predicted the correct sex in 74% of all cases, while the best single variable (OCL) achieved 69.5%. These relatively low classification accuracies reflect the low amount of sexual dimorphism and indicate that these variables should be used with caution when attempting to estimate sex.

The low degree of sexual dimorphic expression within the foramen magnum may be explained by the fact that it reaches the end of growth rather early in childhood [25]. Therefore, no significant secondary sexual changes are expected to develop. Additionally, the prime function of the foramen magnum is to transmit the medulla oblongata and its membranes as well as the spinal component of the accessory nerve into the skull and no muscles act upon its shape and size. Although sex differences of the occipital condyles, whose prime function are to enable the head to move relative to the cervical vertebral column, are low compared to other anatomical regions [26], they are still higher when compared to the foramen magnum. The cranial base’s cartilages are known to resist compression [27] and the atlantooccipital joint is primarily under static strain [28]. However, although loading stresses do not seem to play a major role in influencing dimorphic expression in the occipital condyle, the biomechanical function of the craniocervical joint could be one reason for the increased expression of sex dimorphism in occipital condyles when compared to the foramen magnum. According to Gapert and his colleagues [24], it is more likely that the expression of sexual dimorphism in the occipital condyles is mainly due to genetic rather than epigenetic factors. Therefore, it is important to know the origin of any unidentified skull in order to choose the appropriate population-specific discriminant function formula for estimating sex.