Sex determination through the analysis of the sacrum is an important practice in the study of human skeletal remains. The sacrum is a substantial, triangular-shaped bone formed by the fusion of five sacral vertebrae. It plays a crucial role in the structure of the human body as it constitutes the posterosuperior wall of the pelvic cavity, fitting snugly between two hip bones.[1]

The sacrum serves several key functions as a vital component of the axial skeleton. It supports an upright spine, contributes to the stability of the bony pelvis, facilitates the transmission of weight from the upper body to the lower limbs, and allows for a degree of mobility in the pelvis, which is particularly important during pregnancy.[1]

One of the primary methods for determining sex from the sacrum involves the calculation of the sacral index, a significant metric used in anthropometry. According to the observations of Frazer [2], there are notable differences in the morphology of sacra between sexes. Typically, the female sacrum is broader than the male's and exhibits distinct curvature patterns. In males, the sacrum tends to have a relatively uniform curve extending from the top to the bottom. In contrast, the female sacrum displays a pronounced curvature, particularly marked in the lower section, while the upper part remains comparatively flat. These morphological characteristics underscore the utility of the sacrum in sex determination within forensic and anthropological contexts.

According to Krogman, the accuracy of determining sex from skeletal remains varies based on the specific bones analyzed. When utilizing a complete skeleton, the accuracy rate reaches an impressive 100%. This means that every complete skeleton analyzed can reliably indicate the biological sex of the individual.  When focusing on specific skeletal elements, the combination of the skull and pelvis yields an accuracy of 98%. This indicates that, while the skull and pelvis are strong indicators of sex, there is a slight margin for error compared to a complete skeletal analysis. In cases where only the pelvis is examined, sex determination accuracy drops to 95%. Although the pelvis is crucial in identifying biological sex, factors such as individual variation and potential damage to the remains can affect reliable identification. It's also important to note that the sacrum, which is a critical part of the pelvis, is usually included in examinations for sex determination. Given its consistent anatomical features and role within the pelvic structure, the sacrum contributes to the accuracy of sex determination in human skeletal material. [1]

A study done by Comas and Charles highlighted that there are considerable variations observed in the morphology of the sacrum when comparing male and female specimens within both Chinese and Negro populations.[3].

The present study was conducted on 110 adult human sacra of known sex, 50 of which were male and 60 females. The sacra were dry, free from deformity, and fully ossified. Sacra was obtained from the Department of Anatomy, Index Medical College, Hospital and Research Centre, Indore, Madhya Pradesh, after approval from the college Ethical committee. The sliding vernier calliper was used to measure the maximum length and maximum breath of the sacrum.

Figure: showing the Maximum length of the sacrum

Figure: Showing the Maximum width of the sacrum

The mean maximum sacral length is significantly greater in males (118.6 mm) compared to females (103.7 mm). However, there is no significant difference in the mean maximum sacral width between males (117.31 mm) and females (116.53 mm). Notably, the mean sacral index is higher in females (104.5 mm) than in males (97.54 mm), and this difference is highly significant.

After conducting a thorough analysis of the sacral lengths in males and females, we discovered that the average length of the sacra in males exceeds that of females. This finding highlights a notable difference in sacral dimensions between the two sexes.

This finding aligns with numerous studies conducted across various populations, consistently showing that males tend to be longer than females. [4,5,6] The increased incidence of the six-piece sacrum in males is proposed as a contributing factor to this greater length, and this difference was found to be statistically significant.

In our study, the mean length of the sacrum in males was found to be 118.6 mm, which is significantly greater than the mean length in females, measured at 103.7 mm. This contrasts with a study conducted by Jyothinath K et al. [7], which reported a greater length of the sacrum in females. In another study by Parashuram R et al. [8], the length of the sacrum in males was 120.13 mm, compared to 103.78 mm in females, which aligns more closely with our findings. Additionally, studies by other authors, such as Kataria et al. [9] from Rajasthan and Bindra GS & Mohan A [10] from Haryana, demonstrated similar results.

In our study, we observed that the mean value of the Sacral Index was notably higher in females, recorded at 104.5 mm, compared to 97.54 mm in males. This finding aligns closely with a similar study by Patel ZK et al. [11] in Gujarat, which reported a sacral index of 96.25 mm in males and 113.25 mm in females.

Our findings suggest that the sacral index, along with the maximum sacral length and width, plays a crucial role in determining sex with a positive degree of accuracy. The sacral index is a reliable tool used to determine biological sex by measuring the sacrum, the triangular bone at the base of the spine. This index is important for various fields, including anatomy, where it helps study human skeletal differences; medicolegal work, where identifying individuals accurately is essential; and anthropology, which looks at the traits of different populations. By examining the size and shape of the sacrum, researchers can gather important information about human biology and evolution, highlighting the sacral index's value in both science and practical applications.

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2. Frazer JE. Anatomy of Human Skeleton.3rd ed. London: Churchill Livingstone; 1933.p.3.
3. Comas J, Charles C. Manual of Physical Anthropology. Illinois, USA: Thomas Springfield; 1961: p.415 16.
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