European Journal of Cardiovascular Medicine

Determining the sex of unknown skeletal remains is a critical challenge in fields such as paleoanthropology, paleodemography, and forensic medicine [1]. Accurate sex estimation is essential for reconstructing biological profiles, understanding population dynamics, and aiding in medicolegal investigations. Various methodologies have been explored to determine sex using different bones of the human skeleton, with the pelvic bones being the most reliable due to their distinct functional and structural differences between males and females [2, 3]. These differences are primarily influenced by variations in stature, hormonal profiles, and the unique adaptations of the female pelvis to accommodate childbirth [4]. Among the pelvic bones, the sacrum holds particular significance for sex estimation due to its structural and functional dimorphism, making it a valuable tool in forensic and anthropological analyses [5]. The sacrum, formed by the fusion of five sacral vertebrae and their costal elements, plays a pivotal role in maintaining the stability of the vertebral column and transferring weight to the pelvic girdle [6]. Its morphological characteristics have long intrigued forensic experts and anthropologists, as it exhibits sex-specific variations that can be quantified through morphometric analysis [5]. Historically, Davivongs observed that male bones tend to be larger and heavier than female bones, providing a foundational basis for sex determination [7]. However, relying solely on visual assessments of bone morphology can be subjective and prone to error, highlighting the need for objective, quantitative methods such as morphometric measurements [1]. These measurements have become increasingly important in establishing sexual dimorphism, particularly when dealing with fragmented or incomplete skeletal remains where traditional morphological features may be ambiguous [5]. Despite extensive research on the morphometric parameters of the human sacrum, a single, definitive measurement for sex determination remains elusive. This underscores the importance of utilizing multiple parameters to enhance the accuracy of sex estimation. Previous studies have focused on analyzing sacra of known sex to validate the reliability of various morphometric indices [5]. While radiographs have been used in some studies, direct morphometric measurements of dry sacra are preferred due to the limitations associated with radiographic techniques, such as inconsistencies in film-focus distance, spinal movement, and parallax effects [5]. The sacrum is often regarded as a key bone for sex determination in unidentified skeletal material, yet there is a notable gap in understanding which morphometric parameters are most effective, especially in cases involving fragmented or incomplete remains [5]. This study aims to address this gap by identifying the most reliable morphometric parameters for sex determination in the human sacrum and evaluating their efficacy in distinguishing between males and females. Using the Receiver Operating Characteristic (ROC) curve analysis, we compared various morphometric measurements to establish their diagnostic accuracy in a population from Bihar, India. The findings of this study have significant implications for forensic anthropology, archaeology, and clinical medicine as they provide a more objective and reliable method for sex estimation in skeletal remains. 

This cross-sectional observational study was conducted on 100 dry adult human sacra obtained from the department of Forensic Medicine and Toxicology, Indira Gandhi Institute of Medical Sciences (IGIMS), Patna, Bihar (India), and other medical colleges of the state. Out of these 100 dry adult human sacra, 50 belonged to the male gender, and 50 belonged to the female gender.

Inclusion Criteria:

• Adult human sacra of known sex.
• Complete and well-preserved sacra without significant damage or deformities.

Exclusion Criteria:

• Sacra with pathological conditions, developmental anomalies, fractures, or post-mortem damage that could alter morphometric measurements.
• Immature sacra or those from individuals under 18 years of age, as sexual dimorphism may not be fully expressed.
• Sacra of unknown gender.

Linear measurements were performed with the aid of a digital vernier caliper with a precision of up to 0.01 mm. In this study, the below-mentioned parameters were taken into consideration (Figure 1):

1. Maximum breadth: The distance between the two lateral-most points on the ala of the sacrum is measured as the maximum breadth of the sacrum (from point A to B).
2. Length of the sacrum: The distance in between sacral promontory and the corresponding lowest point in mid sagittal plane on the anterior margin of the sacrum is taken as maximum length of the sacrum (from point C to D).
3. Sacral Index (SI): The sacral index was calculated using the following formula:

SI = (Maximum breadth / Length of the sacrum) X 100.

1. Transverse diameter of the S1 vertebral body: It was measured as the maximum transverse dimension of the S1 vertebral body (from E to F).
2. Height of the S1 vertebral body: It was measured as the vertical distance between the mid-point of the transverse fusion line between the first anterior sacral foramina (ASF) and the mid-point of the promontory (from G to H).
3. Height of the S2 vertebral body: It was measured as the vertical distance between the mid-point of the transverse fusion line between the second anterior sacral foramina (ASF) and the mid-point of the transverse fusion line between the first anterior sacral foramina (ASF) (from H to I).
4. Vertical diameter of the auricular surface (VDA): It was measured as the highest vertical distance between two points, marked at the margin of the auricular surface (from L to M).
5. Height of first anterior sacral foramina (ASF): It was measured as the highest vertical distance between the upper and lower border of the first anterior sacral foramina (ASF) (from J to K).

Height of first posterior sacral foramina (ASF): It was measured as the highest vertical distance between the upper and lower border of the first posterior sacral foramina (PSF) (from N to O).

Figure 1: Showing different landmarks used for morphometric measurement of sacrum.

Statistical Analysis: The collected data was organized into a table using Microsoft Excel 2019. Subsequently, the data was transferred to GraphPad version 8.4.3 for further statistical analysis. Continuous data were expressed as a mean with standard deviations (SD). The morphometric dimensions of male and female sacra were compared using Student’s t-test, and p-values were calculated. The level of significance was set as p-value < 0.05. An analysis of the receiver operating characteristic (ROC) curve was performed to determine the appropriate cut-off values for various measures. The area under the curve (AUC), together with a 95% confidence interval (CI), sensitivity, and specificity, was determined.

A total of one hundred dry adult human sacra were considered to study the sexual dimorphism in various morphometric parameters. The morphometric analysis of the sacrum revealed significant sexual dimorphism across several parameters. The maximum breadth of the sacrum was greater in females (107.57 ± 6.72 mm) compared to males (104.06 ± 8.1 mm), with a statistically significant difference (p = 0.02). Conversely, the length of the sacrum was significantly longer in males (106.61 ± 8.73 mm) than in females (92.29 ± 8.78 mm) (p < 0.0001). The sacral index, which reflects the relative breadth-to-length ratio, was markedly higher in females (117.50 ± 12.49) compared to males (98.17 ± 10.39) (p < 0.0001), indicating a broader and shorter sacrum in fe

males. Regarding the vertebral body dimensions, the transverse diameter of the S1 vertebral body was significantly larger in males (47.27 ± 3.93 mm) than in females (45.13 ± 4.88 mm) (p = 0.018). However, no significant difference was observed in the height of the S1 vertebral body between genders (p = 0.169). In contrast, the height of the S2 vertebral body was significantly greater in males (25.71 ± 2.26 mm) compared to females (24.04 ± 2.40 mm) (p = 0.0005) (Table 1).

Table 1: Showing the different morphometric parameters in sacra of both genders (in mm).

The morphometric analysis of the sacrum, focusing on the right and left sides, revealed significant sexual dimorphism in several parameters (Table 2). On the right side, the vertical diameter of the auricular surface (VDA) was significantly larger in males (54.13 ± 3.82 mm) compared to females (52.20 ± 4.59 mm) (p = 0.024). Similarly, on the left side, males exhibited a larger VDA (54.62 ± 4.65 mm) than females (52.24 ± 4.48 mm) (p = 0.01), indicating that this parameter is consistently greater in males bilaterally. The height of the first anterior sacral foramen (ASF) also showed significant differences between genders. On the right side, the height was greater in males (13.19 ± 1.63 mm) than in females (12.06 ± 1.47 mm) (p = 0.0004). This trend was even more pronounced on the left side, with males having a significantly larger height (13.80 ± 1.58 mm) compared to females (12.15 ± 1.75 mm) (p < 0.0001). Similarly, the height of the first posterior sacral foramen (PSF) demonstrated significant sexual dimorphism. On the right side, males had a greater height (10.90 ± 2.42 mm) than females (9.31 ± 2.59 mm) (p = 0.002). This difference was more marked on the left side, with males exhibiting a larger height (11.48 ± 2.30 mm) compared to females (9.49 ± 2.21 mm) (p < 0.0001).

Table 2. Showing the morphometric parameters of the sacrum (right and left sides) in sacra of both genders (in mm).

ROC analysis of the maximum breadth of the sacrum: Using the Receiver Operating Characteristic (ROC) curve, a threshold for the maximum breadth of the sacra was established to predict the sex of the sacra. A cut-off value of 106.8 mm was determined, providing a sensitivity of 60% and a specificity of 52% in predicting the sex. Sacra with measurements below this threshold were classified as male, while those above it were classified as female. The area under the ROC curve (AUC) was 0.619, with a 95% confidence interval of 0.385 to 0.652 (Figure 2 and Table 3).

Figure 2: Showing ROC curve of the maximum breadth of the sacrum

ROC analysis of the length of the sacrum: Using the Receiver Operating Characteristic (ROC) curve, a cut-off value of 101.7 mm was determined, providing a sensitivity of 78% and a specificity of 86% in predicting the sex. Sacra with measurements above this threshold were classified as male, while those below it were classified as female. The area under the ROC curve (AUC) was 0.869, with a 95% confidence interval of 0.738 to 0.930 (Figure 3 and Table 3).

Figure 3: Showing ROC curve of the length of the sacrum

ROC analysis of the sacral index: Using the Receiver Operating Characteristic (ROC) curve, a cut-off value of 111 mm was determined, providing a sensitivity of 90% and a specificity of 72% in predicting the sex. Sacra with measurements below this threshold were classified as male, while those above it were classified as female. The area under the ROC curve (AUC) was 0.884, with a 95% confidence interval of 0.786 to 0.956 (Figure 4 and Table 3).

Figure 4: Showing ROC curve of the sacral index

ROC analysis of the transverse diameter of the S1 vertebral body: Using the Receiver Operating Characteristic (ROC) curve, a cut-off value of 45.33 mm was determined, providing a sensitivity of 70% and a specificity of 52% in predicting the sex. Sacra with measurements above this threshold were classified as male, while those below it were classified as female. The area under the ROC curve (AUC) was 0.638, with a 95% confidence interval of 0.385 to 0.652 (Figure 5 and Table 3).

Figure 5: Showing ROC curve of the transverse diameter of the S1 vertebral body

ROC analysis of the height of the S1 vertebral body: Using the Receiver Operating Characteristic (ROC) curve, a cut-off value of 28.75 mm was determined, providing a sensitivity of 62% and a specificity of 54% in predicting the sex. Sacra with measurements above this threshold were classified as male, while those below it were classified as female. The area under the ROC curve (AUC) was 0.593, with a 95% confidence interval of 0.481 to 0.741 (Figure 6 and Table 3).

Figure 6: Showing ROC curve of the height of the S1 vertebral body

ROC analysis of the height of the S2 vertebral body: Using the Receiver Operating Characteristic (ROC) curve, a cut-off value of 24.68 mm was determined, providing a sensitivity of 68% and a specificity of 60% in predicting the sex. Sacra with measurements above this threshold were classified as male, while those below it were classified as female. The area under the ROC curve (AUC) was 0.688, with a 95% confidence interval of 0.462 to 0.724 (Figure 7 and Table 3).

Figure 7: Showing ROC curve of the height of the S2 vertebral body

ROC analysis of the vertical diameter of the auricular surface (VDA): Using the Receiver Operating Characteristic (ROC) curve, a cut-off value of 52.91 mm was determined, providing a sensitivity of 65% and a specificity of 60% in predicting the sex. Sacra with measurements above this threshold were classified as male, while those below it were classified as female. The area under the ROC curve (AUC) was 0.642, with a 95% confidence interval of 0.502 to 0.691 (Figure 8 and Table 3).

Figure 8: Showing ROC curve of the vertical diameter of the auricular surface (VDA)

ROC analysis of the height of the first anterior sacral foramina (ASF): Using the Receiver Operating Characteristic (ROC) curve, a cut-off value of 12.58 mm was determined, providing a sensitivity of 73% and a specificity of 63% in predicting the sex. Sacra with measurements above this threshold were classified as male, while those below it were classified as female. The area under the ROC curve (AUC) was 0.731, with a 95% confidence interval of 0.532 to 0.718 (Figure 9 and Table 3).

Figure 9: Showing ROC curve of the height of the first anterior sacral foramina (ASF)

ROC analysis of the height of the first posterior sacral foramina (PSF): Using the Receiver Operating Characteristic (ROC) curve, a cut-off value of 9.85 mm was determined, providing a sensitivity of 70% and a specificity of 54% in predicting the sex. Sacra with measurements above this threshold were classified as male, while those below it were classified as female. The area under the ROC curve (AUC) was 0.693, with a 95% confidence interval of 0.604 to 0.781 (Figure 10 and Table 3).

Figure 10: Showing ROC curve of the height of the first anterior sacral foramina (ASF)

Table 3: Showing the ROC curve analysis of different morphometric parameters of the sacrum

Sex estimation is a fundamental procedure for forensic anthropologists. Determining the sex of compromised or fragmented skeletal remains is challenging, particularly following catastrophic disasters [8,9]. Morphological techniques for sex estimation are less dependable than metric procedures. Osteometric norms for sex estimate are not universally applicable across populations because to variations influenced by genetic and environmental factors, as well as occupation and lifestyle. Therefore, it is imperative to create interim representative skeletal collections for population-specific anthropological requirements [9,10]. Anatomists, forensic specialists, and anthropologists continually strive to develop novel techniques for more precise sex identification based on various skeletal elements. The sacrum is a crucial bone, serving as the extension of the vertebral column and the pelvic girdle bones. This study was undertaken to examine the morphometric parameters of the sacrum in order to determine sexual dimorphism.

This study on the Bihar population revealed that the mean maximum breadth of the sacrum was greater in females, aligning with the findings of Isaac et al. in a Nigerian population, Kumar et al. in an Arabian population, Bakici et al. in a Turkish population, and Mishra et al., Arora et al., Kumar et al., and Parashuram et al. in an Indian population [2,5,9,11-14]. Additional researchers, such as Elkhateeb et al. in an Egyptian cohort and Sachdeva et al., Ravichandran et al., and Bhanarkar et al. in an Indian cohort, documented diminished values in female sacra [1,4,15,16]. In the ROC analysis, we noted that the greatest width exhibited a lower AUC value of 0.619, which is similar to the result reported by Bakici et al. (AUC value = 0.55). Therefore, it may be asserted that greatest breadth alone is not an effective criterion for distinguishing the sex of the sacra. The average sacrum length was larger in males in this study, consistent with the findings of other researchers. In the ROC analysis, the AUC value for the length of the sacra from the promontory to the apex was 0.869 in our study, compared to 0.63 in the research by Bakici et al. involving an Egyptian population [9]. Consequently, the length of the sacrum serves as a reliable metric for sex determination, especially within the Indian demographic. In our study, the sacral index was higher in females, consistent with the results of other studies [1,2,5,11-16]. The ROC analysis revealed that the sacral index had the greatest AUC value of 0.884 among all parameters evaluated for sex determination. Therefore, the sacral index serves as an effective criterion for determining the sex of the sacra. The transverse diameter (TD) of the S1 vertebral body was greater in men in this study, aligning with the results of other researchers [1,4,5,12,13]. The AUC value for the transverse diameter (TD) of the S1 vertebral body in the ROC analysis was 0.638. Consequently, the transverse dimension (TD) of the S1 vertebral body is not a reliable metric for determining the sex of the sacra. No research was found on ROC analysis of sacral characteristics, including the height of the S1 and S2 vertebral bodies, VDA, and the height of the first ASF and first PSF, following a comprehensive literature survey. In this study, ROC analysis of the parameters indicated moderate values for the height of the S2 vertebral body (AUC = 0.688; p = 0.001), the height of the first ASF (AUC = 0.731; p < 0.0001), and the height of the first PSF (AUC = 0.693; p < 0.0001) in determining the sex of sacra in the Indian population (Table 3). Consequently, these criteria can be employed to ascertain sex with an accuracy ranging from 60% to 90%, even in the presence of merely fragmented sacra.

Limitations of the study: The primary limitation of this study was the relatively small sample size, which may restrict the generalizability of the findings. Future studies should aim to include a larger and more diverse sample from the same region to validate and enhance the reliability of the results. Additionally, we recommend further research exploring other morphometric parameters of the sacrum, particularly in cases where only fragmented or incomplete skeletal remains are available. Such investigations could provide more comprehensive tools for accurate sex estimation in forensic and anthropological contexts.

This study emphasizes the importance of various morphometric factors in determining the sex of the sacra. The ROC analysis indicates that the sacral index is the most effective morphometric indicator for this purpose, achieving the highest AUC value of 0.884. Additionally, the length of the sacrum serves as another reliable parameter for sex determination, with an AUC of 0.869. Furthermore, when only a fragmented sacrum is available, the height of the S2 body, the height of the first anterior sacral facet (ASF), and the height of the primary posterior sacral foramen (PSF) can provide accuracy rates between 60% and 73% for sex assessment. This research highlights the significance of morphometric parameters of the sacrum in sex determination, especially in medicolegal situations where the skull and pelvis are fragmented or cannot be accessed. The findings aim to contribute to a reference database of morphometric parameters for identifying the sex of sacra in the Bihar population.

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