This study examined the distal articular surface of the fibula to determine sex from skeletal remains in a Caucasian American sample. Discriminant function analysis correctly classified 85.2% of females and 89% of males using measurements of left distal fibulae. Linear regression found that age had little influence on fibular measurements. The study developed population-specific discriminant functions that could aid in developing a biological profile and narrowing the number of potential victims using partial skeletal remains.

1. Sex Determination Using the Distal Articular Surface of the Fibula
Michelle U. Tabencki
California State University, Los Angeles Los Angeles, CA 90032
Conclusions
Results: Intra-Observer Error
Results: Linear Regression Analysis
Literature Cited
Introduction
Results: Discriminant Function Analysis
Sex Predicted Group
Membership,
Female
Predicted Group
Membership,
Male
Total
Original Count
Female
98 17 115
Original Count
Male
10 81 91
% Female 85.2 14.8 100.00
% Male 11.0 89.0 100.00
Materials
Depiction of PA, PB, PC, LLM and LMF measurements
Discriminant function analysis correctly classified 84.3% of
female right fibulae and 86.8% of male right fibulae.
Sex Predicted Group
Membership,
Female
Predicted Group
Membership,
Male
Total
Original Count
Female
97 18 115
Original Count
Male
12 79 91
% Female 85.2 14.8 100.00
% Male 11.0 89.0 100.00
• A Caucasian sample from the William M. Bass Skeletal
Collection from the University of Tennessee, Knoxville was
used for this study.
• This blind study consisted of 206 pairs of fibulae (115
females, 91 males) of known age, sex and ancestry. Age
range was 25-89 years old. Fibulae with obvious traces of
pathological conditions were excluded from analysis.
Measurements were taken with digital calipers and
rounded to the nearest 0.1mm.
•Population specific discriminant functions were
developed from this sample.
• Linear regression analysis was conducted to examine the
relationship between age and fibular measurements to rule
out the possibilities of age related biases.
• 25 fibulae were randomly drawn and re-examined in
order to determine the degree of intra-observer error.
Discriminant function formulas were developed for left
and right fibulae and an indeterminate range was
calculated to a 95% confidence interval.
Discriminant function for distinguishing male and female
left fibulae:
DF = -14.953 + 0.242X1 + 0.253X2 + 0.169X3 + -0.055X4 +
0.214X5
X1 = LMF, X2 = PA, X3 = PC, X4 = PB, X5 = LLM
Scores:
>1.0765 male
<-0.8435 female
1.0765 and -0.8435 indeterminate (95% confidence interval)
Discriminant function for distinguishing male and female
right fibulae:
DF = -15.128 + 0.253X1 + 0.331X2 + 0.141X3 + -0.081X4 +
0.200X5
X1 = LMF, X2 = PA, X3 = PC, X4 = PB, X5 = LLM
>1.0805 male
<-0.8395 female
1.0805 and -0.8395 indeterminate (95% confidence interval)
Linear regression examined the relationship between age
and fibular measurements within age brackets
• Age Bracket: 0yr-49yrs for left and right fibulae
•R² value 0.088, indicating younger age has little
influence on measurements taken from left fibula
•R² value 0.043, indicating younger age has little
influence on measurements taken from right fibula
• Age Bracket: 50yrs-100yrs for left and right fibulae
• R² value 0.017, indicating older age has little
influence on measurements taken from left fibula
• R² value 0.090, indicating older age has little
influence on measurements taken from right fibula
25 randomly selected samples were taken from the original
206 sample
• PA, PB, PC, LLM had a percentage error of zero
• Margins were well defined and simple to measure
• LMF had a percentage error of 1.2%
•Landmarks in this measurement are more difficult
to locate due to the sloping nature of the sides of the
malleolar fossa. During data collection, the calipers
were placed on the very bottom of the slope at the
maximum diameter of the fossa.
• Using population specific discriminant functions for both
right and left fibula, it was found that the left fibula of both
sexes had higher correct classification results than the right
fibula, with females correctly sexed at 85.2% and males
correctly sexed at 89%.
• Linear regression analysis indicates age has little
influence on the fibular measurements. Examination of the
literature revealed that few age-related skeletal changes
occur on the articular surface of the distal fibula. This is
due to thin articular cartilage and uniformity of cartilage
matrix in the ankle, both of which contribute to a rarity of
osteoarthritis in the area (Thomas 2003: 924).
• Intra-observer analysis demonstrated that the PA, PB, PC
and LLM measurements were easily reproducible with an
acceptable amount of error. The margins of the
measurements are well defined on the distal articular
surface.
• Although the LMF measurement percentage error of 1.2%
is still very low, there is a discrepancy as to where exactly to
take the measurement in regards to the sloping nature of
the margins of the malleolar fossa.
While the percentage of specimens correctly
classified was not the same percentage achieved by Sacragi
and Ikeda (1995), it is believed by the researcher that this
population specific discriminant function should be used if
the distal fibula is found and believed to be that of a
Caucasian individual. This study focused on the American
Caucasian population, therefore further research is
warranted to determine if this method is suitable to be used
for other American ancestral populations. Left fibulae have
a higher degree of accuracy than the right fibulae.
Since age has little affect on sex determination, the
technique can be used on suspected younger and older
individuals. From the forensic aspect, human identification
techniques are essential in developing the biological profile
and there can never be too many ways to identify remains.
From the archaeological aspect, fragments of bone are
usually found during excavation. In this sense, there must
be techniques such as this one to be able to identify half of
a population.
Acknowledgements
The author thanks Dr. Dawnie Steadman for access to the UT William M. Bass Collection.
Many thanks to Eric Scott of the San Bernardino County Museum for academic guidance
and support. Thank you to Bone Clones, Inc. for sponsoring this poster presentation.
Abstract
A preliminary step in any forensic investigation is
to identify the victim. This important step involves
developing a biological profile of the skeletal remains. The
forensic anthropologist develops the biological profile by
examining the remains to determine the sex, approximate
age, ancestry, estimated stature and identifying
characteristics of the individual.
Determining the sex of remains cuts the number of
potential victims roughly in half in a given population.
Therefore it is important for anthropologists to understand
the differences that manifest in the skeletons of males and
females. It is critical to gain data on all skeletal elements for
use in cases where only part of the remains are recovered. A
population specific discriminate function correctly
classified 85.2% of females and 89% of males using left
distal fibulae. Linear regression analysis indicates that age
has little influence on the fibular measurements.
Methods Results: Discriminant Analysis Cont. Discussion
Discriminant function analysis correctly classified 85.2% of
female left fibulae and 89% of male left fibulae.
Sacragi, A., Ikeda, T.
1995 Sex Identification from the Distal Fibula. International Journal of
Osteoarchaeology 5:139-143
Thomas, RH., Daniels, TR.
2003 Ankle Arthritis. The Journal of Bone and Joint Surgery 85-A(5): 923-936
The distal fibula was measured in 5 dimensions
• Perpendicular distance from the antero-superior apex
(apex A) to the side BC is designated perpendicular A (PA)
• Perpendicular distance from the inferior apex (apex B) to
the side AC is designated perpendicular B (PB)
• Perpendicular distance from the postero-superior apex
(apex C) to the side AB is designated perpendicular C (PC)
• Distance from apex A to the apical point of the lateral
malleolus is designated the length of the lateral malleolus
(LLM)
• Bilaterally directed maximum diameter of the malleolar
fossa was designated the bilateral diameter of the lateral
malleolar fossa (LMF)
(Sacragi 1995: 140)
In the forensic and anthropological literature, the
fibula has not been extensively explored for its potential to
determine sex. The most notable study was conducted by
Sacragi and Ikeda (1995) where measurements of the distal
articular fibula were taken based on dimensions that are
closely related to soft tissues. Through the use of a
population specific discriminate function, Sacragi and
Ikeda were able to correctly classify males at 90.1% and
females at 91.4%.
This research investigates the distal fibula for its
potential to determine the sex of skeletal remains using a
Caucasian American population.