Sexual dimorphism in the Humerus : south IndiansCorrespondence Address :
Department of Anatomy, S N Medical College, Navanagar,
The present study aimed to detect the possibility of sex discrimination from the humeral measurements in south Indians. One hundred normal right humeri were taken from one hundred cadavers (54 males and 46 females) who were above 20 years of age and who belonged to the south Indian population. Six measurements of the maximum length, vertical head diameter, midshaft circumference, minimum midshaft diameter, maximum midshaft diameter and epicondylar breadth were taken from each humerus. The measurements were statistically analyzed.
Sexual dimorphisum, Humerus, Osteometry
The facility for personal identification, at present, is making rapid progress because of the development of the polymerase chain reaction (PCR) and stereolithography (1) (2).
The determination of sex is a very important component of any human skeletal analysis. Sex estimation in a complete human skeleton is usually easy by the observation of morphological traits (3).
Sex discriminatory functions which are obtained for each bone are very useful in mass disasters and criminal cases of multiple human burials, where charred bodies and scattered, mixed or incomplete remains are recovered. Since the osteometric methods for the determination of sex from the skeleton are population specific, researchers from around the world have conducted studies to establish group- specific standards of assessment (4).
Many bones have been previously used for the identification of sex, and such studies emphasize that sexual dimorphism starts to appear after puberty.(5) The humerus has rarely been tapped as a site for sex determination, though it has often demonstrated an even greater accuracy than other long bones such as the femur. (6)(7) Therefore, the purpose of this research was to establish osteometric standards for the determination of sex from the humerus in south Indians.
The present work was carried out on 100 right humeri (54 males and 46 females) which belonged to the south Indian population. They were collected from the anatomy departments over 3 years. The bone samples were dissected and extracted from adult cadavers.
Samples with any pathological changes, fractures or the nonunion of the epiphysis of the head were excluded.
The collected bones were socked in a saturated solution of sodium chloride for 4- 6 weeks, and were then boiled in water with a pinch of sodium carbonate for 20-25 minutes. All adherent soft tissues were removed and the bones were dried for 2 days (8).
Six dimensions were taken for each humerus (to the nearest millimeters) by using an osteometric board (Table/Fig 1), a sliding caliper (Table/Fig 2) and a steel tape. The measurements included maximum length (V1), vertical head diameter (V2), midshaftcircumference (V3), minimum midshaft diameter (V4), maximum midshaft diameter (V5) and epicondylar breadth (V6) (Table/Fig 3) The Studentâ€™s t test was used to determine the mean standard deviation (SD), standard error (SE) and the variance for each variable in both the sexes. The T and P values were estimated, and the level of significance was set at 0.05. The data were also statistically analyzed by using the main from the SPSS program, version 6 (1988)(9).
The distance between the sex means (d/s) was also determined from the ratio of the mean difference and the mean standard deviation, to demonstrate the overlap between the male and the female samples.(10) The following formula was used: d/s= (Xm-Xf) √ (nM s2 M + nF s2 F) / (nM + nF) (Xm-Xf= means, nM, nF= examined samples; s2M, s2F variance in two samples). The mean difference (Xm-Xf) is the difference of the means of the males and females. Mean standard deviation is the square root of the ratio between the sample variance (males and females) and the total sample size. d/s was calculated to demonstrate the overlap between the male and the female samples.
The cut off level, the value which maximized the sum of the sensitivity and specificity, was determined for each variable by using the Receiver Operating Characteristic (ROC) curve (11). Various combinations to the measurements from V1 to V6, were also analyzed by using the ROC curves. Then, the sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and the accuracy for each variable were detected separately and in combination.
The results of the descriptive statistical analyses are represented in (Table/Fig 1) revealing the mean, standard deviation, standard error and the variance of each variable. The t values for comparisonbetween the males and females and their significance are given. Also, the distance between the sex means (d/s) were recorded.
(Table/Fig 4) shows that the mean values of males were significantly higher than those of the females in all measurements (p<0.001). The standard deviations denoted that males exhibited more variability than females in all the variables.
The maximum length (V1) was the measurement with the greatest sex difference (d/s=2.07), followed by the midshaft circumference (V3) with d/s= 1.83, the minimum midshaft diameter (V4) with d/s= 1.77, epicondylar breadth (V6) with d/s= 1.74 and, the vertical head diameter (V2) with d/s= 0.47. The mean values of the six measurements in males and females are illustrated in (Table/Fig 5). The efficacy of the sex determination from each variable was tested by using the ROC curves to detect their cut off values. Measurements which were equal to or higher than the cut off levels indicated a male individual and lower values indicated afemale individual. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and the accuracy for each variable are shown in (Table/Fig 6).
The results revealed that the measurements of males weresignificantly higher than those of the females (P<0.001). The maximum length was the most discriminating variable in sex determination, with a 90% rate of accuracy, followed by midshaft circumference (86%) and the minimum midshaft diameter (82%). A combination of the two variables revealed that the minimum midshaft diameter with the epicondylar breadth gave the highest rate of accuracy for correct sex prediction, with accuracy rate of 88%. The results of this study can help in the prediction of sex from the humerus in south Indians, when other human remains which are suitable for sex determination, are not available.
The maximum length (V1) was the measurement with the greatest sex difference (d/s=2.07), followed by the midshaft circumference (V3) with d/s= 1.83, the minimum midshaft diameter (V4) with d/s= 1.77, epicondylar breadth (V6) with d/s= 1.74 and, the vertical head diameter (V2) with d/s= 0.47. The mean values of the six measurements in males and females are illustrated in (Table/Fig 7). The efficacy of the sex determination from each variable was tested by using the ROC curves to detect their cut off values. Measurements which were equal to or higher than the cut off levels indicated a male individual and lower values indicated afemale individual. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and the accuracy for each variable are shown in (Table/Fig 6).
(Table/Fig 6) shows that the accuracy of the sex measurements ranged from 58% to 90%. The maximum length (V1) was the first for sexual dimorphism, with the highest accuracy rate for sex prediction (90%). Midshaft circumference (V3) came next with an accuracy of 86%, followed by minimum midshaft diameter (V4) with an accuracy of 82%, maximum midshaft diameter (V5) with an accuracy of 80%, epicondylar breadth (V6) with 74% accuracy and finally, vertical head diameter (V2) with 58% accuracy. Also, from Table (2), it is clear that maximum length was the most sensitive variable for the identification of the male individuals (88.9%) and that it also had the highest rate of negative predictive values (87.5%) . It was followed by epicondylar breadth (sensitivity = 88.9% and NPV = 85.7%). Also, maximum length was found to be the most specific variable for the determination of the female sex (91.3%) and it also had the highest rate of positive predictive value (92.3%).
A variety of combinations between each of the two different variables were tested in order to make them more useful and these are shown in (Table/Fig 7).
It was obvious that the combination between V1 and V2, V2 and V6, V3 and V6 and V5 and V6 gave 100% sensitivity to themale sex and 100% negative prediction for females. Meanwhile, the combination between V4 and V6, V1 and V3 and V1 and V4 gave the highest rate of accuracy (88%). This is followed by the combination between V1 and V5 and V1 and V6 (86% each). The combination between V2 and V4 gave the lowermost rate of accuracy (74%).
Sex determination is the first essential step for positive identification when a decomposed body is recovered. It is essential to identify sex from different bones of the body, other than the skull or the pelvis. Many studies have set osteometric standards for sexual dimorphism.(4) In addition, populations have different morphological and metric manifestations in both the sexes (12). Therefore, it is necessary to have population specific standards from skeletal collections (13).This study aimed to determine sex by using different measurements of the humerus which belonged to south Indians. All the cases in this study were above 20 years of age, as this was the age of the epiphyseal union of the head of the humerus and its shaft, with no further growth in the bone length (5).
The results have revealed that the mean values of the male measurements were significantly higher than those of the females. For example, the mean value of the maximum length (V1) was 32.10Â±1.58 and 28.95Â±1.45 in males and females respectively. The sexual difference of the humeral measurements was previously discussed by Iscan et al.(14), who studied the sexual dimorphism of the humerus among the Chinese, Japanese and the Thai populations. They found that the mean values of V1 were 31.37Â±1.646 and 28.36Â±1.368 in the Chinese, 29.74Â±1.042 and 27.69Â±1.71 in the Japanese and 30.06Â±1,565 and 27.89Â±1.367 in the Thai populations. The sex difference in the humeral measurements was explained by Black(15), who proposed that differential bone remodeling exists between the males and females, in addition to the development of more cortical bone during adolescence in the males.
The present study revealed that the maximum length (V1) was the measurement with the greatest sex difference (d/s= 2.07). The reliability of sex determination from each variable was tested by the analysis of the ROC curves and the maximum length (V1) was found to be the most sensitive one (88.9%) with the highest rate of accuracy (90%). This was followed by midshaft circumference- V3 (86% accuracy) and minimum midshaft diameter- V4 (82% accuracy). On the contrary, Iscan et al. (1998)(14) found that the most effective single dimension, as determined by the direct discriminate analysis, was the vertical head diameter (V2) in the Chinese (81%) and epicondylar breadth (V6) in the Japanese and the Thai populations (90% and 93% respectively). Also, Wu (1989) (6) reported the greatest dimorphism in the proximal and distal bone dimension during his study on the northeastern Chinese population. He found that the humeral head diameter was the most common sex discriminator (84%).
Gray and Wolfe (1980)(16) stated that stature based sexual dimorphism peaks in societies that are at the extremes of protein consumption, both high and low. In addition, DiBennardo and Taylor(17) suggested that shape measurements are of major significance for the correct diagnosis of sex, because the functional demands of weight bearing and musculature affect the circumferential measurements more than the length. Kranioti EF, and Michalodimitrakis M(18) studied 168 left humeriby the osteometric method and they found 92.3% accuracy in determining the sex. They found that the single most effective (89.9%) dimension was the vertical head diameter of the humerus. Robinson MS and Bidmos MA(19) got a 72-95.5% accuracy in their study on the skulls and humeri of South Africans (Europian Deescent).
A combination of the more sex differentiating measurements provided a higher rate of accuracy. A combination of the minimum midshaft diameter and epicondylar breadth (V4 and V6) gave the highest rate of accuracy (88%) and this seemed to be the most reliable one. This was followed by a combination of the maximum length and midshaft circumference (V1 and V3) and a combination of the maximum length and the minimum midshaft diameter (V1 and V4), with an accuracy rate of 88% for each. On the contrary, Iscan et al,(14) selected four variables for the Chinese and Japanese and three variables for the Thais. The only dimensions which were common to all the groups were epicondylar breadth and vertical head diameter, while maximum length was present as a factor only in the Chinese. They found that the highest rate of accuracy was 86, 8% in the Chinese, 92.4% in the Japanese and 97.1% in the Thais.
The degree and the distribution of sexual dimorphism vary both within and between the different regions. Therefore, most skeletal biologists agree that the interpopulation difference necessitates the development of regionally specific standards for the identification of sex. This study underscores the need for medicolegal investigations and also for the study of population affinities and factors which affect bone configurations.
It must be noted that the patterns of sexual dimorphism differ between populations and that the results which were obtained, could not have similar accuracy if they were applied to different ethnic groups. This study confirms the reliability of sex identification from the humerus and the reported results can be considered as a valid support for the medicolegal investigations which involve the skeletal remains of south Indians.
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