Dimorphism in Femora: An Indian Study
Department of Anthropology
Former Director and Founder
In the field
of forensic osteology, determining sex from skeletal remains, especially
from isolated bones, has been an age-old problem. This study documents
efforts to determine sex by using five measurements from the femur.
The study is based on 200 male and 80 female femora from central
India. The data are analyzed using discriminant function procedures,
and results of different measurements are reported independently
and in various combinations. Three variables combined into a function
could correctly assign sex to 92 percent of males and 96.3 percent
The role of
the skeleton in estimating attributes such as age, sex, race, stature,
and the presence of disease is discussed by Krogman and Iscan (1986).
They stated that the record of organic evolution is largely written
by the hard parts of the body recognizable even after many years
of death. Sex determination from skeletal remains, which forms an
important component in the identification procedure, sometimes becomes
a difficult task for the forensic anthropologist, especially in
the absence of the pelvis. Therefore, most of the long bones, either
individually or in combination, have been subjected to statistical
and morphological analysis for the purpose of determining sex. So
far, several studies conducted for assessing sex from various skeletal
parts have reiterated that there is a size difference between populations
and that metric standards must be developed for each group. Citing
the example of the femur, studies have been reported on various
populations including the Finns (Lofgren 1956); French (Godycki
1957); Japanese (Hanihara 1958); Australian aborigines (Davivongs
1963); English (Steel 1972); American blacks, whites, and Indians
(Black 1978; DiBennardo and Taylor 1979 and 1982; Iscan and Miller-Shaivitz
1984 and 1986); Italians (Pettener 1979); Czechs (Cerny and Komenda
1980); prehistoric Scottish (MacLaughlin and Bruce 1985); archeological
remains of Sudanese Nubians, Pecos Pueblo Indians, and Arikaras
(France 1988); Chinese (Liu 1989; Iscan and Shihai 1995); Spanish
(Trancho et al. 1997); Nigerians (Asala et al. 1998); Thais (King
et al. 1998); South African whites and blacks (Asala 2001; Steyn
and Iscan 1997); and Germans (Mall et al. 2000). Little work on
the subject has been reported from India except for the study by
Singh and Singh (1972A and 1972B) on the head of femur. To date,
nothing has been published on other measurements of the femur, which
may be useful if the bone is fragmented. This study is an attempt
to examine the sexual dimorphism in femora of Indian origin.
This study on
sexual dimorphism is based on the principle that the axial skeleton
weight of the male is relatively and absolutely heavier than that
of the female (William et al. 1989), and the initial impact of this
weight is borne by the femur in transmission of the body weight.
Another factor that makes its indentation on the femur is the modification
of the female pelvis with respect to its specialized function of
reproduction. Therefore, the stress and strain experienced by the
femur is different in a male than it is in a female.
Data for this
study are comprised of 280 dry adult femora from 200 male and 80
female residents of central India. The collection was housed at
the Medico-Legal Institute of Bhopal, India. Abnormal or pathologically
deformed bones were excluded from the study. Most of the bones in
the collection, stored since 1973, are forensic specimens, and only
a few are unclaimed specimens. Every care had been taken by the
authors to include bones from a homogenous population. Information
on probable age at death, race, sex, date of arrival, and probable
cause of death were well documented in a register after examination.
The bones were preserved in iron boxes coded with a serial number.
In order to
test for bilateral variation in the measurements, 20 sets of femora
were subjected to a paired t-test. The difference was found to be
insignificant at the 0.05 level, thus allowing the bones of both
sides to be grouped together. However, only one bone, either left
or right, has been included in the analysis. A set of five anthropometric
measurements was taken on each femur: maximum length, maximum diameter
of the head, midshaft circumference, maximum anteroposterior diameter
of the femoral shaft, and epicondylar width. Maximum length, midshaft
circumference, and epicondylar width were measured following the
standard techniques recommended by Martin and Saller (1957). Maximum
head diameter and maximum anteroposterior diameter were measured
following the technique given by Brauer (1988) and MacLaughlin and
Bruce (1985). The latter had measured the maximum anteroposterior
diameter of the shaft between superiorly, the inferior margin of
gluteal ridge, and inferiorly, the level at which the two lips of
the linea aspera diverge to form the supracondylar lines. A Mitutoyo-dial
caliper was used to measure the maximum head diameter, the maximum
anteroposterior diameter, and the epicondylar width nearest to 1/100
Data were analyzed
using the SPSSX Subroutine software (SPSS Incorporated, Chicago,
Illinois). Stepwise discriminate function analysis employing measurements
was used to determine the optimal combination of variables for assessing
sex. Variables, alone and in combination, were also subjected to
direct analysis to develop functions to allow sex determination
from fragmentary remains. To further test the efficiency of the
discriminant functions derived from the previous analysis, they
were applied to a randomly chosen test group of 43 femora (29 males
and 14 females). The test group was not a part of the original sample
but did consist of bones of the same class and population as the
This study used
measurements taken for five variables. Table
1 shows the routine statistical analysis of these variables
accounting for various measurements. The standard deviations are
given with an F-ratio for each measurement. With the average male
skeleton being longer, more muscular, and heavier than the average
female, all the measurements in Table
1 exhibit a highly significant sex difference. The combined
coefficient of variation for male and female in the table exhibit
highest relative variation in the sample for maximum anteroposterior
diameter of the femoral shaft. Table
2 gives the summary of the stepwise discriminant function analysis.
The data are reported under three headings: the Wilk's Lambda, equivalent
F-ratio, and calculated degree of freedom. The table shows that
out of five variables entered, four were selected for the analysis.
Once the epicondylar width was analyzed, the remaining variables
were reassessed and selected according to the Lambda level. The
maximum anteroposterior diameter having the least Lambda value was
entered from the remaining variables as Step 2. Included in the
analysis were the maximum head diameter as Step 3 and the maximum
length as Step 4. The analysis was terminated after Step 4, probably
because of the extremely low value of F-ratio of the remaining variable,
which was below the threshold of criteria for entrance.
the stepwise discriminant function analysis, the variables were
entered directly to provide various combinations, some of which
may be used for fragmentary remains. The functions and their coefficients
are presented in Table 3. The raw
coefficients are used to calculate the discriminant scores for the
functions. The sectioning point has been set to zero. As a result,
when the product of the predictor variable and its coefficient added
to the constant is above zero, the individual can be classified
as male. If the product added to the constant is below zero, the
individual can be classified as female. The standard coefficient
column indicates the contribution of a variable to the discriminant
score relative to other variables. In this study, epicondylar width
has the maximum discriminating power. The structure coefficient,
the next column, gives an idea of what a variable contributes to
a function on its own. Again, epicondylar width has the highest
4 presents the percentage of correct group membership. This
gives the accuracy of prediction for each function. The first column
shows the accuracy for males, the second for females, and the last
shows the average for both sexes. These functions can be grouped
into four categories. In the first category using a single variable
(Functions 1-5), the accuracy ranges from 84.3 to 91.1 percent,
and the best discriminator is maximum head diameter. It is interesting
to note that, although the F-ratio value for epicondylar width is
greater than maximum head diameter, it is probably the latter's
smaller relative variation in the sample (coefficient of variation
= 5.59) that is responsible for its edge over the former (coefficient
of variation = 5.77).
second category uses two variables in combination (Functions 6-8),
which can be used when one or more anatomical areas are damaged.
The combination of epicondylar width and maximum head diameter gives
92.1 percent accuracy. The third category, consisting of Function
9 using three variables in combination, shows a marked increase
to 93.2 percent in prediction accuracy. The last category (Function
10) is the result of stepwise analysis; although four variables
are used in combination, the prediction accuracy remains unchanged.
The results of discriminant functions that were applied on the original
sample were applied on the test cases and presented in Table
5. The success rate of identification was lower when compared
to the original sample on Table 4.
This was expected, because the sample from which the functions had
been drawn gives maximum accuracy for the same sample compared to
any other sample, although drawn from the same population. Table
6 exhibits the results of cross testing the Indian data using
formulae of Thai, Chinese, American whites, and South African whites
and contrasts them with accuracies obtained from their original
studies. The American white formula identified only 19 percent of
the males and classified most of the males as females. The result
of the South African formula is similar, exhibiting a slight improvement
(27 percent for males). The results of Chinese (58.5 percent) and
Thai (63.5 percent) formulae are comparatively better, although
nowhere near the accuracy attained on the Indian sample using its
own population-specific formula (93.2 percent).
It is known
that the average male skeleton is longer and more robust than the
average female, although the magnitude of difference varies from
population to population. This sex difference can be the result
of genetic factors, environmental factors affecting growth and development
(nutrition, physical activity, and pathologies), or the interaction
of these factors (Trancho et al. 1997). The results of this study
show that the femoral extremities display higher classification
accuracy (91.1 percent for maximum head diameter and 89.6 percent
for epicondylar width) than shaft dimensions. The extremities of
the bone are the areas where a number of muscles make their insertions
and are subjected to more pull than at the point of origin. Also,
as suggested by France (1988), the articular surfaces of the bone
receive a portion of the force being applied across them, and as
such, the extremities of the femur will react to such forces.
while working on Portuguese femora, had opined that the head diameter
and width of the lower end discriminated sex better than any other
part of the bone. Of the 17 variables analyzed by Van Gerven (1972)
for sex difference by discriminant function, epicondylar width in
isolation produced the greatest male-female discrimination. Dittrick
and Suchey (1986) also concluded that the ends of the femur produced
10 percent greater accuracy than either femoral length or midshaft
circumference. In most of the recent studies on Spanish (Trancho
et al. 1997), Chinese of Qingdao and Changchun cities (Iscan and
Shihai 1995), and South African whites (Steyn and Iscan 1997), the
extremity measurements proved better, with epicondylar width outdoing
head diameter. It is the reverse for the present sample and also
among northeastern Chinese, as reported by Liu (1989).
determination with maximum anteroposterior diameter was discussed
by MacLaughlin and Bruce in 1985, its efficacy has not been tested
on many populations. The results of this study confirm that the
diameter is a good indicator of sex, with classification accuracy
reaching 85.7 percent. Maximum anteroposterior diameter of the femoral
shaft is directly related to the muscle attachment to the bone.
Several muscles make their insertion at the linea aspera, which
is the area of measurement. Males generally use their muscles more
powerfully due to both heavier body weight and additional action,
resulting in greater pull at the insertions. Moreover, the diameter
of the shaft is related to the weight borne by the femur. In males,
the axial skeleton weight is relatively and absolutely more than
that of female (William et al. 1989).
It is a common
experience for the forensic expert to be confronted with poorly
preserved or fragmentary bones. Because of the tubular structure
of long bones, they are often better preserved than other shorter
bones. This long bone measurement has an additional advantage. Unlike
some of the previous studies, this study shows that the midshaft
circumference measurement displays less classification accuracy
than length measurement.
4 demonstrates that there is a gap in the accuracy between sexes
for all the functions, with the females being consistently on the
higher side. This is probably due to the combined effect of the
unequal sample size and the intrasex variation.
variation is graphically represented in Figures 1 and 2. Comparison
has been made between the results of those recent studies where
at least four variables are common. All the measurements of the
present study, both male and female, are comparable to Thai data
except for male maximum femoral lengths that are closer to American
whites. The nearness of data of the present study to the Thai sample
does not indicate any racial proximity. It does indicate that, on
the average, the girth (midshaft circumference) of the Indian male
is nearly equal to the girth of the American female, white and black.
As can be seen in Table 6 for American
whites and Thai populations, stepwise discriminant function formulae
have been used for cross testing. This is in contrast to Chinese
and South African whites where other suitable functions were selected
to be applied on the present sample, because stepwise formula used
variables not included in the present study. Ignoring this limitation,
when the results of the cross testing are compared, it is evident
that among the four populations, the Thai formula gave the best
results. This was expected, because all the dimension values of
the Indian population (except for maximum length in males) were
closest to the Thai sample.
Thus, this study
reconfirms the fact that osteometric assessment is highly population-
specific. It may be added that more studies are required in south
Asia to give a better picture of the racial variation that exists
there and to offer more osteometric standards for assessing sex.
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