European Journal of Cardiovascular Medicine

The human skeleton has its medicolegal importance in identifying race, sex, and stature. Experts are always facing a problem in identifying whether the skeletal remains are human as well as estimating the correct age, sex, and height of the specimen available. Accurate determination of skeletal sex and sex has been a critical issue and the accuracy depends on the nature of the material available and the methods applied. [1-3]

Multiple works have been done and ample literature is available in forensic anthropometry for the identification of human skeletons. For medico-legal purposes, the examination of the human skeleton is an integral part. Whether the bone is of a male or a female from unknown human skeletal or decomposed bodies is the first pivotal step in forensic investigation. If the whole skeleton is available for examination, we can identify the sex(male/ female) with almost 100% accuracy. When only the skull or pelvis is available, sex may have been determined with 90% accuracy. If no skull and pelvis are available, it becomes difficult to determine the age and sex accurately [4].

To a medicolegal expert, the manubrio-sternal and xiphi-sternal articulation are valuable for the estimation of age. The shape and length of this bone help in the determination of sex also. The age-wise length of the manubrium and ratio with the other portion of the bone, and whole length (i.e., length of manubrium and length of the body) of the sternum with the whole length of the body again may give information regarding the stature of the individual. Considering all these aspects, the study of the human sternum is being carried out with the expectation of successful outcomes.

In an old age paper in 1881, it was seen that Dwight measured 30 male and 26 female sterna in the Harvard Medical School. He recorded manubrium length, mesosternum length, and total length. The average manubrium length was 51.8 mm for males and 46.7 mm for females. The average mesosternum length was 105.8 mm for males and 89.5 mm for females. The average total length was 157.7 mm for males and 136.2mm for females. The sternal index was reported to be accurate for 60% of males, and 46.2% of females. [5]

In the later year in 1889, Dwight measured 142 male and 86 female sterna from the Harvard Medical School. As with his previous study, measurements included manubrium length, mesosternum length, and total length. The average manubrium length was 53.7 mm for males and 49.4 mm for females. The average mesosternum length was 110.4mm for males and 91.9 mm for females. The average total length was 164.1 mm for males and 141.3 mm for females. The sternal index was reported to be accurate for 59.2% of males and 60.5% of females. In both studies, Dwight concluded that while Hyrtl‘s Law was successful when applied to the mean values, it failed when applied to the individual.[6]

In 1956 Ashley stated that the female sterna from both the European and East African samples were smaller than the male sterna. He found the largest difference in measurements occurring between the mesosternum lengths of male and female sterna. Ashley (1956) reported averages of the sternal measurements for both the European population and the East African population. The average manubrium length in the European sample was 52.2 mm for males and 47.9 mm for females. The average manubrium length in the East African sample was 45.9 mm in males and 44.2 mm in females. The average mesosternum length in the European sample was 104.7 mm in males and 90.8 mm in females. The average mesosternum length in the East -African sample was 95.5 mm in males and 82.8 mm in females. The average sternebrae  width in the European sample was 26.4 mm in males and 24.5 mm in females. The average sternebrae 1 width in the East African sample was 24 mm in males and 21.5 mm in females. The average sternebrae width in the European sample was 33.7 mm in males and 30.5 mm in females. The average sternebrae  width in the East African sample was 30.9 mm in males and 26.8 mm in females. The average total length in the European sample was found to be 156.9 mm in males and 138.7 mm in the case of females. In the East African sample, the average total length was found to be 142.6 mm in males and 127.1 mm in case of females. The sterna index was calculated and for the European sample, 52.9% of the males and 69.3% of the females conform to Hyrtl’s Law. In the East African sample, 64.7% of the males and 69.2% of the females conform to Hyrtl's Law. Following the studies mentioned above, Ashley found Hyrtl’s Law to be unreliable, due to large amounts of overlap between male and female values. This was also true for the results of the relative width index. These unreliable tests prompted Ashley to create the sectioning points, based on measurements of total length, known as ‘The 149 Rule’ for Europeans, and The 136 Rule’ for East Africans. Two issues were presented in this article. First, the length of the sternum is related to the height of the individual, meaning the sterna of a tall female could be confused with the sterna of a short male, and vice versa. Furthermore, the second concern is how the length and width of the sternum continue to increase throughout life and this could lead to a difference in the sectioning points, sternal index, and relative width index with age. [7].

In a relatively recent study, Menezes RG et al. stated that the length of the sternum is a liable predictor of stature in adult South Indian females and can be used as a tool for stature estimation when better predictors of stature like the long bones of the limbs are not available when examining skeletal remains. The study was undertaken to estimate stature from the length of the sternum in South Indian females using a linear regression equation. A linear regression equation [Stature = 111.599 + (3.316 × Length of the sternum)] was derived to estimate stature from the length of the sternum. The correlation coefficient was 0.639. The standard error of the estimate was 4.11 cm. [8]

Human Sternum from the cadavers in the Kolkata Police Morgue under the Dept of Forensic Medicine and Toxicology, Medical College & Hospital, Kolkata, being brought for medico-legal autopsy examination in the Department (May 2021—April 2022) were included in this current cross-sectional observational study. The sternum was examined after getting the IEC (Ref. No.- MC/KOL/IEC/NON-SPON/972/01/2021) and being screened through inclusion and exclusion criteria.

Study material –Human Sternum

Study sample - 100 dead bodies (55 males and 45 females) were taken by complete enumeration method from dead bodies brought to the Kolkata Police morgue, depending on the inclusion and exclusion criteria. 36 sterna were broken at the time of processing and cleaning. So finally, 64 sterna were analyzed where 38 were Male and the rest 26 were female.

Inclusion Criteria –

1. Dead subjects with known sex & age.
2. Age Group---18 years & above. The age of the deceased was obtained from the nearest relatives and police and was verified by necessary documents. The age of the deceased was rounded off to full figures.
3. Sex --Both male & female.

Exclusion Criteria –

1. Subjects with fracture of the sternum.
2. Subjects with the pathology of the sternum.
3. Subjects with deformities of sternum.
4. Unknown or unclaimed dead bodies where age cannot be confirmed.

Technique - The sterna were removed from the cadavers by sectioning the costal cartilages just beside the costochondral junction. Then after processing and treatment with chemicals, the measurements were done.

Measurements were taken in millimeters, with the help of Vernier Calliper-

1. Length of manubrium (ML) - It is the distance from the suprasternal notch to the Manubrio-mesosternal junction in the midline.
2. Length of mesosternum (SL) - It is the distance from the manubrio-mesosternal junction to the mesosterno-xiphoidal junction in the midline.
3. Combined length of the manubrium and mesosternum/ Total Length (TL) = ML+SL

Table 1 -- Distribution of the study population according to age. (n = 64)

From the above table, we can see the greatest number of cases were from the age group of 18-39 years.

Table 2: - Overall descriptive statistics for the study population for both sexes.

Table 2 represents the summary of the descriptive statistics as mean, standard deviation, and standard error of the mean for the longitudinal metrics of the sternum bone considering the overall data without categorizing into age groups for both sexes

The overall mean along with the standard deviation for males was 52.44±4.10 mm, and 98.44 ± 13.61 mm. Manubrial length, and Mesosternal length respectively. Whereas, in the case of female subjects these measurements were 45.19 ± 3.67 mm, 83.20 ± 11.88 mm respectively.

Table 3:- Statistical discussion of length of Manubrium (ML) for sexual dimorphism.

Table 4:- Independent Samples T-test of Length of Manubrium (ML) for Male and Female Comparison

The above tables (Tables & 4) represent the independent “t” test done to compare the mean manubrial length of the sternum between males and females. There were significant differences in the mean manubrial length of the sternum between the male and female groups.

An independent samples t-test was used to compare the mean ML score of males (n=38) and females (n=26) deceased. Neither Shapiro-Wilk statistic was significant, indicating that the assumption of normality was not violated. Levene’s test was also non-significant; thus, an equal variance can be assumed for both groups. The t-test was statistically significant, with the mean ML score of males (M=52.44, SD=4.10) significantly higher (mean difference 7.24, 95% CI [5.24, 9.25]), than the females (M= 45.19, SD=3.67), t (64) =7.23, p<.001, two-tailed, Hedges’s gs = 1.819. The common language (CL) effect size indicates that the chance that for a randomly selected pair of individuals, the ML score of a male is higher than the score of a female is 80%.

Table 5. The mean difference in Length of Manubrium (ML) scores between male and female students

Table 6. Statistical discussion of Length of Mesosternum (SL) for sexual dimorphism.

Table 7 Independent Samples T-test of Length of Mesosternum (SL) for Male and Female Comparison

The above table represents the independent “t” test done to compare the mean length of the mesosternum (SL) of the sternum between males and females. There were significant differences in the mean length of mesosternum (SL) of the sternum between the males non-significant; thus, an equal variance can be assumed for both groups. The t-test was statistically significant, with the mean SL score of males (M=98.44, SD=13.61) significantly higher (mean difference 15.24, 95% CI [8.65, 21.82]) than the females (M= 83.20, SD=11.88), t (64) =4.62, p<.001, two-tailed, Hedges’s gs = 1.162965. The common language (CL) effect size indicates that the chance that for a randomly selected pair of individuals, the MW score of a male is higher than the score of a female is 80%.

Table 8. The mean difference in Length of Mesosternum (SL) scores between male and female students

Table 9. Variables in the analysis

From Table.12, Wilk’s λ of a canonical discriminant function was 0.479, the Chi-square value was 44.945, and P< 0.001, meaning that there was a statistically significant discriminant score difference between groups. Because the P value was less than 0.05, it was decided that the model was a good fit for the data (Tables 18 & 19)

Unstandardized canonical discriminant function coefficients of variables are shown in Table 11.

 The unstandardized canonical discriminant function was estimated using two variables:

D= (0.211* ML) + (0.37* SL) -13.845

The standardized canonical coefficients and the structure weights reveal that two (Manubrial length and Mesosternal length) of the four variables contributed to the multivariate effect. The best predictor for distinguishing between male and female sternum was the body Length of Mesosternam (SL).

Manubrium Length (ML)

Average manubrium length (ML) was provided by multiple studies. Results of populations in India are presented by Hunnargi et al [9]. Gautam et al [10]., Dahiphale et al [11], and Jit et al [12]. Dahiphale et al [11] provide the lowest values for average ML of the studies, reporting 43.78 mm for males and 48.46 mm for females. The highest values of those studies are found in Gautam et al [10]. with average ML in males being 53 mm, and in Jit et al. with 48 mm in females. The European populations are represented by Ashley [13] and Teige.[14] Ashley reports the highest average ML for males was 52.2 mm and 47.9 mm for females. Teige reports the lowest average ML for males was 47.7 mm and 43.9 mm for females. Ashley also presents information on an East African population with the average ML in males being 45.9 mm and 44.2 mm in females. McCormick et al. [15] report the highest ML with 55.6 mm for males and 50.3 mm for females. The lowest values for average ML are reported by Dwight [16] with 51.8 mm for males and 46.7 mm for females. Torwalt and Hoppa [17] represent the Canadian population and report the average ML as 54.431 mm for males and 48.793mm for females. According to these averages of ML, the lowest values are found in the population from Western India for females and East Africa for males. The highest values are found in the United States for both males and females. A number of the studies provided sectioning points for ML. Hunnargi et al [9] report that values greater than 57 mm were male, and values less than 43 mm were female. Gautam et al. [10] report that values greater than 63 mm were most likely males and values less than 33 mm were most likely females. McCormick et al. [15] report that values greater than 60 mm were males and values less than 46 mm were females. the present study is in agreement with the findings of Gautam et al, Dahiphale et al [11], Jit et al [12], and Rother et al. [34] in that, there is no significance found in ML regarding sex estimation.

Mesosternum Length (SL)

Average mesosternum length (SL) was reported in multiple studies. The lowest average SL in populations from India was reported by Hunnargiet al. [9] as 89.17 mm for males, and by Dahiphale et al [11]. as 70.19 mm for females. Jit et al. [12] provided the highest SL for both males and females at 95.35 mm and 78.6 mm, respectively.

Teige [14] provided the lowest average SL for the European populations, with 103.4 mm for males and 88.5 mm for females. Ashley [7] provided the highest average SL with 104.7 mm for males and 90.8 mm for females. Ashley [7] also presents information on an East African population with an average SL of 96.5 mm for males and 82.9mm for females. The average SL in the present study, with 116.97 mm for males, and 105.35 mm for females. The highest average SL is reported by Dwight et al. [16] with 110.4 mm for males, and 91.9 mm for females. Torwalt and Hoppa [17] report the Canadian average as 109.409 mm for males, and 93.551 mm for females. According to these averages of SL, the lowest values are found in the Western Indian populations for both females and males. The highest values are found in the United States for males and in Canada for females. A few of the studies provided sectioning points for mesosternum length. Hunnargi et al. [9] report that values greater than 95 mm are male, values less than 65 mm are female, and a sectioning point of 81 mm yields an accuracy rate of 73.3% for males and 75% for females. Gautam et al [10] report that values greater than 106 mm were male, and values less than 48 mm were female. Dahiphale et al. [11] report that values greater than 88 mm were considered, male, and values less than 76 mm were considered female. This study is in agreement with the previous research in that the SL proves to be more sexually dimorphic than the other elements, but due to high percentages of overlap, it is not the most reliable indicator of sex when used alone.

The great Professor Bernard Knight once said that the determination of sex is statistically the most important criterion, as it immediately excludes approximately half the population whereas age, stature, and race each provide points within a wide range of variables. The current study showed that the pre-defined linear vertical length of the sternum proves to be an almost accurate indicator of sex. Through the use of metrics of the sternum, the sex of the individual can be estimated using corresponding accuracy rates. Utilizing metrics yields an objective estimation of sex, unlike the subjective method of visual assessment. In addition, metrics allow less experienced individuals to utilize this research and provide accurate estimations of sex, without relying on years of experience for confidence or familiarity with methods involving visual assessment. In the current study, an attempt was made for a paradigm shift from morphological to morphometrical dimension.

In the current study, the study population comprises 38 (59.4%) males and 26 (40.6%) females, selected through the complete enumeration method. Among total 64 cases of the present study 28(43.8%) cases are from 18-39 years age group and 22 (34.4%) cases are from 40-59years age group 14(21.9%) cases are from 60-90years. On considering sex, it is found that the mean length of manubrium in male(52.44mm) is greater than that of female (45.19mm). The mean length of body in male(98.44cm) is greater than that of female (83..20cm).

Most importantly unstandardized canonical discriminant function was estimated using two pre-defined vertical linear measurements as independent variables (Manubrium Length-ML and Mesosternum Length-SL) as below:-

D= (0.211* ML) + (0.37* SL) -13.845

FUNDING: This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors.

ACKNOWLEDGMENT: We are sincerely thankful and grateful from core of our heart to Prof (Dr.) Biswajit Sukul, Professor and Head of the Department, FMT of Gouri Devi Medical College to act as the orchestra master of our study

CONFLICT OF INTEREST: The authors declare that there is no conflict of interest. This research work is a part of the dissertation of the First Author, submitted at the West Bengal University of health sciences in compliance with partial fulfillment of eligibility for the MD Examination for the year 2022.

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