Bull. Natl. Mus. Nat. Sci., Ser. D, 34 pp. 43–51, December 22, 2008

New Method for Diagnosis of the Sex and Age-at-death of an
Adult Human Skeleton from the Patella
Kazuhiro Sakaue
Department of Anthropology, National Museum of Nature and Science,
3–23–1 Hyakunincho, Shinjuku-ku, Tokyo 169–0073, Japan
E-mail: k-sakaue@kahaku.go.jp

Abstract The diagnosis of sex and age-at-death from the adult human skeleton is very importantin the field of physical and forensic anthropology for the identification of a human body. Threestudies of the diagnosis of the patella reporting an accuracy of approximately 85% have been published; however there is no study about diagnosis of the age-at-death on the basis of morphology ofthe patella. The purpose of this study is to calculate the discriminant function for sex in recent
Japanese skeletons and develop a new method for age estimation by analysis of the patella. In thisstudy, 283 recent Japanese skeletal materials (183 males and 100 females) were used. The correctly classified percentages of the discriminant functions with all the variables reached at 85%. However, the age estimation by analysis of the patella was not as reliable as that by the analysis of
pubic symphysis or cranial sutures. It can be said that the age estimation by analysis of the patella
is rather vague; therefore its usage should be limited for a vague estimation of age, and age-atdeath evaluated by this method may be expressed as young (score 0), middle-aged (score 1), andold (sores 2 and 3).
Key words: Patella, Discriminant analysis, Recent Japanese, Age estimation, Sex diagnosis.

Introduction
The diagnosis of sex and age-at-death from theadult human skeleton is very important in thefield of physical and forensic anthropology forthe identification of a human body. There aremany studies on the metric or non-metric diagnoses of sex or age-at-death from bones.
In practice, whether or not these methods canbe utilized primarily depends on the preservationof a skeleton. For example, the morphology ofthe pubic symphysis is widely used as an indicator of age-at-death (White, 2000). However, since
the os pubis is rarely preserved in archaeologicalor forensic specimens, this excellent method can
not be utilized in many cases. Even if some of
the methods of assessment of sex or age-at-death
are utilized, the discrepancy is observed between
the results of the different methods used.
This problem can be addressed by developing
many methods of diagnosing the sex or age-at-

death by analyzing various parts of a skeleton.
This will increase the possibility of diagnosis thesex or age-at-death. Further, a more reliable diagnosis could be achieved by utilizing many of theavailable methods and performing a comprehensive assessment by using these results.
There are three studies concerning diagnosisof the sex by analyzing the patella (Introna et al.,
1998; Bidmos et al., 2005; Dayal et al., 2005).
These studies determined sex as the discriminantfunctions calculated using six metric variablesfrom three populations as the Italians (40 males,
40 females; Introna et al., 1998), South Africans
of European descent (60 males, 60 females; Bidmos et al., 2005), and South Africans of African
descent (60 males, 60 females; Dayal et al.,2005). The correctly classified percentages inthese studies reached over 80%. Thus, it was
concluded that the discriminate functions withthe measurements values of the patella can beutilized for diagnosis of the sex.

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Kazuhiro Sakaue

However, the sample sizes of these studies
were limited to below 120 individuals. Moreover,these methods could not be applied in Asian populations because of statistically significant difference between ethnical populations in the metrical
data of the patella was reported by Dayal et al.
(2005).
There is no study about diagnosis of the ageat-death by the analysis of the morphology of thepatella. Woo et al. (1986) used rabbit medial collateral ligament to demonstrate that young rabbits were more subjected to ligament avulsion at
its attachment to the bone, whereas older rabbits
were more likely to suffer midsubstance tearingof ligament or bone fracture. This indicated thatthe stiffness of the inter-connection between thecollagens of ligaments and bones increases withage. Yamada et al. (2004) investigated age-related changes of elemental contents at the insertion
tendons in humans and showed that the composite elements such as Ca and Mg increased significantly with aging suggesting that age-relatedbone changes can be observed at the sites of ligament-to-bone or tendon-to-bone attachments.
Osteoarthritis frequently occurs at knee joints.
It has been suggested that the degenerativechanges caused by osteoarthritis are related toaging (Aufderheide and Rodriguez-Martin, 1998).
Degenerative changes of the patella can be recognized as eburnation on the articular facet andsevere osteophytes around the articular cartilage.
There is the possibility that these degenerativechanges may cause the morphological changes
with increasing age, especially at the attachmentof the quadriceps femoris muscle and the marginof the articular facet.
The purpose of this study is to calculate thediscriminant function for sex in recent Japaneseskeletons and develop a new method for age estimation by analysis of the patella.
Material and Methods
The 283 recent Japanese skeletal materials(183 males and 100 females) used in this study
belong to the University Museum of the Univer-

Fig. 1. Distribution of the recent Japanese skeletal
samples.

Fig. 2.

Definitions of patella measurements.

sity of Tokyo and the Department of Anatomy,
Chiba University School of Medicine; the Graduate School of Social and Cultural Studies,
Kyushu University; and Shinshu University schoolof Medicine. The sex and age-at-death of thesesamples, which were collected between 1880s
and 1960s, were recorded. Figure 1 showed the
distribution of the skeletal, which ranged from 14
to 83 yearsold.
For the discriminant analysis, six measurements, whose definitions were followed Martin’s
measurements (Baba, 1991), were used (Fig. 2).
Both right and left patella were measured.
In order to devise a method for estimating the
age-at-death, the existence of the bone lipping at
the attachment of the quadriceps femoris muscle
and the existence of the regressive marginal osteophytes at the margin of the articular facet wereobserved. The composite score method, which
was used for estimating the age-at-death by theDiagnosis of Sex and Age-at-death from Ppatella

Fig. 3. Definition of the morphology of lipping at the attachment of the quadriceps femoris. These patellae wereon the right side. The left side of each picture was shot in the frontal views and the right one was in thefrontal-lateral view. The status of bony lipping was examined on the area surrounded by the dot line. SCORE
0 indicates no lipping, SCORE 1 indicates weak lipping with jaggy, SCORE 2 indicates remarkable lipping.

45

46

Kazuhiro Sakaue

Fig. 4. Definition of the morphology of the dual edge of the margin of the articular facet. These patellae werealso on right side. The articular margin surrounded by the doted line showed no dual edge of the bottom picture and the dual margin of the top one.

cranial suture method (Meidle and Lovejoy,1985) and the auricular surface method (Buckberry and Chamberlain, 2002), was used in thisstudy. The lipping at the attachment is formed
through a gradual degenerative transition fromno lipping to the remarkable lipping. This transition can be divided conveniently into three stage;no lipping, weak lipping with jaggy on the surface of the attachment of the quadriceps femorismuscle, and the remarkable lipping observed as
outgrowth of greater than 1 mm from the smoothsurface of the attachment of the quadriceps.
Scores of 0, 1, and 2 were assigned for thesethree stages (Fig. 3). Strictly speaking, theregressive marginal osteophyte can only beobserved in individuals that suffered from osteoarthritis of the knee. If this serious regressive
marginal osteophytes were counted, the averageage of the existence of this lipping would deviate
to over 60 years (Lawrence, 1963). However thedual edge of the margin of the articular facet canbe observed in the individuals of approximately
30 years who have no symptom of osteoarthritis,
and the real marginal osteophytes can be regarded as the bony extension of the outer edge of thisdual one in individuals with osteoarthritis. Thus,
the articular margin without the dual edge was
assigned the score 0 and that with the dual edge,
score 1 (Fig. 4). The composite score is definedas the sum of the scores of these morphologicalDiagnosis of Sex and Age-at-death from Ppatella

characteristics and the mean age and standard deviation of each composite score was used for estimating the age-at-death.
Statistical analysis was carried out using the
one-sample Kolmogorov–Smirnov test was conducted for all variables in each sex to test for any
deviations from the normal distribution. The distribution of all variables of each sex did not differ
from the normal at a statistically significant level.
The Kolmogorov–Smirnov test, however, resulted
in rejection of a normal distribution in almost allcomposite scores in both sexes at the 1% significance level. Therefore, non-parametrical tests
were performed for aging parameters.
The one-sample t-tests and the Wilcoxon
signed rank tests were performed for the side differences. All variables showed no statisticallysignificant side differences at the 5% level.
Therefore, only the results of the right side havebeen reported in this paper.
The two-sample t-test and the Mann–Whitney’s
U test for sexual differences were performed.
Subsequently, discriminant analyses were performed, and the discriminant functions, Wilk’s
lambda, and the correctly classified percentages
were calculated.
In the analysis of the composite score for estimation of the age-at-death, the Mann–Whitney’s
U test was used in order to determine whether theadjacent scores were significantly different. If
statistically differences were observed, the mean
age of the composite score can be safely used for
estimating the age-at-death.
Table 1.

47

For evaluating these methods, the 26 recent
Japanese skeletal materials (15 males and 11 females) were investigated subsequent to theabovementioned analyses. Thus, the data of thisindependent sample were not included in developing the diagnosis methods of sex and age-atdeath by analyzing the patella. All this samples
were stored in Chiba University School of Medicine. For the test of diagnosis of sex, the measured values were applied to the discriminate
functions. For test of estimation of the age-atdeath, the mean errors between the estimated andreal ages (inaccuracy and bias) were calculated(Lovejoy et al., 1985; Sakaue, 2006). The inaccuracy was calculated as the estimated age real–age /n, showing the average magnitude of absolute error. Bias was calculated as the estimatedage–real age /n, expressing tendency for either
over- or under-estimation of age.
In this study, statistically significance was set
at 5%. All statistical analyses were performed
using the statistical software package SYSTAT
10.2.
Result and Discussion
Diagnosis of the sex
Descriptive statistics of all variables are presented for each sex in Table 1. Results of the six
measurements are shown in Table 1. All the variables showed statistically significant sexual differences with the two-sample t-test.
The results of the discriminant analyses are

Basic statistics of the six variables of the patella for sex diagnosis in recent Japanese.
Male

Maximum Height
Maximum Breadth
Maximum Thickness
Articular Height
Breadth of the Medial Facet
Breadth of the Lateral Facet

FemaleMean(S.D.)

Mean(S.D.)

41.1
43.5
19.4
30.9
21.5
27.5

(2.7)
(3.0)
(1.5)
(2.2)
(1.8)
(2.2)

36.6
39.1
17.7
28.3
19.3
24.5

(2.1)
(2.5)
(1.3)
(1.7)
(1.5)
(2.1)

The sample size is 283 individuals (183 males, 100 females).
There is no statistically significant differences between the right and left.
All varibales have statistically significant differences between sex.

48

Kazuhiro Sakaue

Table 2.

Summury results of discriminat analyses for sex from the mesurements of the patella.

Maximum Height
Maximum Breadth
Maximum Thickness
Articular Height
Breadth of the Medial Facet
Breadth of the Lateral Facet
constant
Wilk’s Lambda
Correctly classified (%)

Function No. 1

Function No. 2

Function No. 3

Function No. 4

0.258
0.044
0.167
0.037
0.182
0.143
17.578

0.294
0.161
0.078

0.282
0.141

16.926

17.0520.061
0.205
0.326
0.21017.323

0.525
85.0%

0.545
85.0%

0.546
85.0%

0.587
84.0%

Table 3. Sexing accuracy for recent Japanese with using three discriminat functions published in other ethnic
populations.

Male
Female
Total

Italian(correctly %)South Africans
white(correctly %)South Africans
black(correctly %)

146
79
225

(79.8)(79.0)(79.5)

117
96
213(63.9 )
(96.0 )
(75.3 )

117
96
213

(63.9)(96.0)(75.3)The most accurate function (83.8%) with “maximum width” and “Maximum Thickness” in Italian was reported in
Introna et al. (1998), the most accurate function (85.0%) with “all six variables” in South African of European decent
was reported in Bidmos et al. (2005), the most accurate function (85.0%) with “maximum breadth”, “maximum height”
and “maximum thickness” in South Africans of African descent was reported in Dayal et al. (2005).

presented in Table 2. The correctly classified percentages of the discriminant functions with all
the variables was 85%, which is almost comparable to the result of the best functions obtained inprevious studies (83.8% in Italians (Introna et al.,1998), 85.0% in the South African black (Dayalet al., 2005), and 85.0% in the South African
white (Bidmos et al., 2005). Surprisingly, thecorrectly classified percentages were approximately 85% in all the functions in this study. In
previous studies, the maximum length andbreadth were consistently the variables exhibiting
the maximum difference between the sexes(Dayal et al., 2005; Bidmos et al., 2005). Thiswas confirmed to be the same percentage of thefunction No. 3 as those of functions No. 1 andNo. 2 in this study.
Table 3 shows the result of application of thebest discriminant functions in previous studies tothe recent Japanese skeletal samples of this study.
The correctly classified percentages of thesefunctions were under 80%. This means that thediscriminate power of the discriminant functionof the patella developed for one ethnic population will reducel when applied to another ethnic
population.
It can be said that this method for diagnosis of
the sex from the patella with the discriminantfunctions can be practically applied to Japaneseskeletal specimens.
Diagnosis of the age-at-death
Table 4 shows the mean age and standard deviation of each composite score, and Figure 5
shows the box plot of composite score for thesexes. It is clear that the variation in each score
was very wide even at the younger score (0 or 1)
and all the standard deviations exceeded 10.0. In
the Suchey–Brooks system for age estimation by
analysis of the pubic symphysis, the standard deviations at younger phases as phase I (the mean
age in male, 19.0) and phase II (the mean age inmale, 25.3) was lower as 2.5 and 4.9 respectively
in recent Japanese male (Sakaue, 2006). Even theDiagnosis of Sex and Age-at-death from Ppatella
Table 4.

49

Basic statistics for each composite score in the recent Japanese and Mann–Whitney’s U tests.
Male

FemaleComposite score
0

N

Mean

(S.D.)

98

32.5(14.6)N

Mean(S.D.)

52

31.8(11.8)

*
1

37

43.2

*

(13.6)

12

48.8(13.6)

*
2

29

50.1

(13.2)

3

19

57.2

(15.8)

*
*

18

58.8

(11.3)

18

60.7(12.7)“*” means statistically significant between Phases or Sexes at 5% level.

patella were not as reliable as that by analyzing
the pubic symphysis or cranial sutures. Judging
from no significant difference between score 2
and 3, the number of scores in this method was
only 3 in practice. Therefore, it can be said thatage estimation by analysis of the patella is rather
vague, therefore, its usage should be limited forthe vague estimation of age-at-death in term of
three classes: the young (score 0), the middle
aged (score 1), and the old (score 2 and 3).

Fig. 5. Box plot of the composite score for estimating age-at-death evaluated by analysis of
the patella.

highest value of the standard deviation in the
Suchey–Brooks system was 12.1 at phase VI (themean age in male, 58.4). In the age estimation
method with cranial sutures developed by Meindl
and Lovejoy (1985), the highest value of the standard deviations was 12.6.
Age differences between scores 0 and 1 andbetween scores 1 and 2 were statistically significant, but differences between scores 2 and 3 did
not reach statistical significance in both sexes.
These results indicated that the age estimation
by analyzing the morphological variations of the

Test of the method
The results of the test by using 26 recent
Japanese skeletal materials are presented in Table
5. All the female samples were correctly classified and the 4 male individuals were incorrectlyclassified, and the percentage of correctly classified specimens was 84.6%. Therefore, the diagnosis of sex with the patella is considered to bean effective method. The mean inaccuracy of theanalysis was 8.6, which is higher than that reported in Suchey–Brooks systems used to assess
recent male Japanese (5.6). The mean bias was
slightly positive at 0.7, but this value is incidental. Since an error of over 10 years was obtained
in determining the age-at-death of 9 individuals,
diagnosis of the age-at-death by analysis of thepatella cannot be considered effective.
In summary, the discriminant functions of thepatella was effective for the diagnosis of the sex
in Japanese skeletal samples, the method of age-50

Kazuhiro Sakaue
Table 5.

The result of the application of the new metods to the recent Japanese.

Sample No.

Sex

Age

Discriminant scores

Estimated age

Bias

Inaccuracy

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26

f
f
f
f
f
f
f
f
f
f
f
m
m
m
m
m
m
m
m
m
m
m
m
m
m
m

71
20
41
32
23
20
31
43
68
64
33
39
63
51
20
28
40
39
52
41
17
30
56
30
45
27

1.976
1.452
1.848
1.501
0.854
1.4101.898
3.187
0.659
1.963
2.224
0.4870.272
2.014
0.096
2.337
1.144
0.608
0.229
1.2300.565
0.535
1.003
2.220
0.672
2.512

48.8
31.8
31.8
31.8
31.8
31.8
31.8
48.8
60.7
60.7
48.8
32.5
43.2
32.5
32.5
32.5
43.2
32.5
43.2
43.2
32.5
32.5
50.1
32.5
32.5
32.5

22.2
11.8
9.2
0.2
8.8
11.8
0.8
5.8
7.3
3.3
15.8
6.5
19.8
18.5
12.5
4.5
3.2
6.5
8.8
2.2
15.5
2.5
5.9
2.5
12.5
5.5

22.2
11.8
9.2
0.2
8.8
11.8
0.8
5.8
7.3
3.3
15.8
6.5
19.8
18.5
12.5
4.5
3.2
6.5
8.8
2.2
15.5
2.5
5.9
2.5
12.5
5.5

0.7

8.6

Average

84.6%

The bold-itallic characters mean the misclassified socres of sex.

at-death estimation developed in this study was
not very accurate. Nevertheless, this method
could be used for obtaining a vague estimate of
the age-at-death, and this is the only method thatcan be used for age estimation by analysis of thepatella.
Acknowledgments
I wish to express my gratitude to Dr. G. Suwa
(The University Museum of the University ofTokyo), Drs. T. Chiba and Dr. C. Mori (Chiba
University School of Medicine), Drs Y. Tanaka
and Dr. T. Nakahashi (Graduate School of Social
and Cultural Studies, Kyushu University), and
Dr. S. Moriizumi (Shinshu University school of
Medicine), for permission to access skeletal materials and for their valuable advice.

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