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Effects of field size when using Kerley's histological method for determination of age at death.

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AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 58:123-125(1982)
Effects of Field Size When Using Kerley’s
Histological Method for Determination
of Age at Death
SAMUEL D. STOUT A N D SARAH J. GEHLERT
Department of Anthropology, University of Missouri, Columbia, Missouri
65211
KEY WORDS Osteon, Age estimation, Field size, Histology, Bone
ABSTRACT
The field size at which a bone is read affects the results obtained
when using Kerley’s histological method for age estimation, even after applying
the recommended correction factor. Whereas there is no tendency for any one of
three field sizes tested to consistently underestimate or overestimate age, a field
size closest to that used by Kerley in his original study had significantly lower
variances for its age estimates, and thus provides greater reliability. This particular field size yields more precise estimates because it is sampling a pattern and
number of structures more similar to that of Kerley.
Correction factors cannot equalize the counts of osteons and osteon fragments
because of spatial variations in the distributions of these histological structures.
A field size similar to that used by Kerley in gathering the data from which he
developed his regression equations must be used to assure that the same pattern
and number of structures is being sampled. For this reason, we suggest a field size
as close to 2.06 mm2as possible be used when employing Kerley’s method.
It has been well established that differences
in field size can introduce error when employing Kerley’s (1965) histological aging method
(Ubelaker, 1977.) Since the field size that is
observable at the same magnification, but with
different oculars and objectives can vary considerably, a correction factor has been recommended that will make the observed field size
comparable to the original field size used by
Kerley in developing his regression formulas
(Kerley and Ubelaker, 1978).
A great deal of spatial variation has been
reported within the cortex of bone (Amprino
and Marotti, 1964; Frost, 1969). Merely adjusting osteon counts in proportion to differences in field size, therefore, may be of
limited value. The purpose of this study is to
investigate the limitation of the field size correction factor currently recommended for
Kerley’s histological aging method.
MATERIALS AND METHODS
A sample of twenty femoral sections from
twenty individuals was used in this study; all
were obtained from dissecting room
specimens. These individuals were well
0002-9483/82/5802-0123$01.~~
. 1982 ALAN R. LISS, INC
documented as to age, sex, and cause of death.
The sample consisted of nine females and
eleven males. The age range was 13-95 years,
with a mean of 55 years.
A Nikon microscope with a l o x objective
was used with three different l o x oculars,
each of which produced a different sized field of
view. The area of each field was measured with
a stage micrometer. Following the procedure
suggested by Ubelaker (1977),correction factors were derived by dividing each of the field
sizes into Kerley’s estimated original field size
of 2.06 mm2.Our first field, using a Nikon wideangle ocular, had a diameter of 1.90 mm. This
yielded an area of 2.83 mm2which, when multiplied by 0.73, the correction factor for this ocular, gives the desired corrected field area of
2.06 mm2(Kerley and Ubelaker, 1978).The second ocular, an aus Jena wide-angle,had a measured field diameter of 1.70 mm, and an area of
2.27 mm’. The correction for this ocular was
0.91. The third ocular was a Merz, with a
square reticulated grid, which measured 1.03
Received October 2. 1980; accepted September 14. 1981
124
S.D. STOUT AND S.J. GEHLERT
mm2 with an area of 1.06 mm2. I t s correction
factor was 1.94.
The number of osteons, osteon fragments,
and non-Haversian canals was counted at each
field size using the methods described by Kerley (1965).Each of these counts was multiplied
by the appropriate correction factor. Age
estimates were computed from each of the corrected counts using Kerley’s revised regression equations (Kerley and Ubelaker, 1978).
Corrected counts of osteons, osteon fragments, and non-Haversian canals were first
compared. Differences in the corrected counts
among the three field sizes were determined for
each variable for the 20 femora. The mean and
standard deviation of the differences for each
of the variables was computed, and a t-test applied to determine whether the mean difference
in corrected counts for any field size differed
significantly. The same procedure was used to
compare the differences in age estimates derived from each field size, and to determine
whether any of the age estimates derived from
each field size, differed significantly from the
known age.
RESULTS
Results of the t-test of mean differences between corrected raw counts for the 20 femora
showed that one of nine variables differed
significantly from zero (see Table 1).This mean
difference was of the number of osteon
fragments between the 2.83 mm’ and the 1.06
mm’ field sizes.
None of the mean differences between age estimates were found to be significantly different for any of the three field sizes (see Table 1).
When estimated age and known age were
compared for each count at each field size,
three of the nine estimates differed significantly from known age (see Table 2). Those differing significantly were ages estimated from
the non-Haversian canal regression equations
for all three field sizes. Variances were lowest
for all counts taken at the 2.27 mmz field size.
Two of these counts, those based on the number of osteons and the number of osteon
fragments, had significantly lower variances,
using the F statistic, than did the variances for
all other counts (see Table 2).
DISCUSSION
Field size differences of the magnitudes
represented in this study have little effect
upon age prediction using osteon and osteon
fragment counts when the correction factor
described by Kerley and Ubelaker (1978)is introduced. Non-Haversian canal count,
however, significantly underestimated actual
at all three field sizes. Kerley’s equation for
this measurement truncates at 58.39 years,
and, therefore, cannot be applied to older ages.
Since 40% of our sample is over the age of 58
years, this probably acounts for the observed
tendency towards underestimation.
Although none of three field sizes showed a
tendency to consistently underestimate or
overestimate age, the field size closest to that
reportedly used by Kerley in his original study
exhibited a significantly lower variation in differences between known age and age predicted
from osteon and osteon fragment counts.
Therefore, for any given case, there is a significantly greater reliability for age prediction
when a field size similar to that used by Kerley
(1965) is employed, even when the proposed
correction for field size difference is
introduced.
Within the cortex of bone, structures are not
uniformly distributed i.e., there is a great deal
of spatial variation (Amprino and Marotti,
1964; Frost, 1969).This spatial variation may
be the reason that the field size closest to Kerley’s original size gives more precise age estimates when using his regression equations.
If all structures, such as osteons and osteon
fragments, were evenly distributed throughout the cortex, one could read at any field size.
Since this is not the case, it is necessary to use
a field size similar to that which was used to
determine the original regression equations in
order to assure that the same patterns and
structures are being sampled. This suggests
that care should be taken when using Kerley’s
method to use a field size as close as possible to
2.06 mm2.
Spatial variation may also account for why
the 1.06 mm2 field size showed significantly
higher osteon fragment counts than the other
two field sizes. This field size is smaller than
the others. It thus samples an area which is
both smaller, and more closely situated at the
periosteal edge of the cortex. This evidence
may indicate that the area closer to the periosteum contains a higher concentration of osteon fragments than other areas of the outer
third of the cortex. This observation may also
be due in part to the older age distribution of
our sample. In younger bone samples, the relative number of fragments would tend to be re-
125
FIELD SIZE AND AGE ESTIMATES FROM BONE
TABLE 1. Mean differences between corrected counts and age estimates from fields of different sizes‘
2.83 mm2 field
Count
Osteons
mean
std. dev.
t-value’
Osteon fragments
mean
std. dev.
t-value
Non-Haversian canals
mean
std. dev.
t-value
2.27 mm2 field
2.83 mm’ field
less
less
less
2.27 mm’ field
1.06 mm2 field
1.06 mm’ field
Counts
Ages
- 1.03
Counts
Ages
Counts
Ages
15.19
- 0.30
0.20
12.05
0.07
1.77
16.35
0.48
0.20
12.14
0.08
0.74
14.25
0.23
0.41
11.27
0.16
- 2.11
- 2.23
- 7.45
- 4.49
11.49
- 0.87
- 5.34
12.46
- 1.92
- 2.27
12.17
0.77
10.84
- 0.94
15.11
- 2.20*
- 1.47
- 0.66
1.07
5.32
0.90
-
2.37
1.25
-
0.92
4.83
0.85
0.47
7.65
0.85
-
-
13.64
1.59
5.40
1.31
1.54
8.07
0.27
-
‘Sample size is 20 for all measures.
’The t-value for difference of mean from zero.
*Significance level of P < 0.06.
TABLE 2.Mean differences between actual ages and those estimated from counts of three
different histological structures at three different field sizes (in years)‘
Age estimated
from counts of
Osteons
mean
std. dev.
t-value’
Osteon fragments
mean
std. dev.
t-value
Nan-Haversian canals
mean
std. dev.
t-value
2.83 mm2 field
- 2.15
2.27 mm* field
- 2.35
1.06 mm’ field
- 2.56
15.13
0.64
-
- 4.29
-
10.61
- 1.81
-
-
- 8.62
- 9.08
12.54
- 3.07;;
- 3.19;;
-
7.55
14.37
- 2.35*
6.43t
1.63
2.07
6.46t
1.43
-
14.38
0.79
0.20
12.19
0.07
12.74
‘sample size is 20 for dl measures.
’The t-value for mean difference from zero.
?The squares of these standard deviations, i.e.. the variances of these measures, are. by the F statistic, smaller than those for all other
measures at the P = 0.05 level.
*Significance level of P < 0.05.
**Significance level of P < 0.01.
duced near the periosteum due to the presence
of circumferential lamellae.
ACKNOWLEDGMENTS
B~~~ specimens used in this study were
made
through the courtesy Of Dr’
Roy
Department Of Anatomy and
Neurobiology, Washington University School
of Medicine, and Dr. William Goodge, Departmerit of Anatomy, University of ~
i
~
ri-(=oumbia School of Medicine. T L research
was funded in part by grant AM 22118 from
the National Institute of Health.
LITERATURE CITED
Amprino, R, and Marotti G (1964) A topographic study of
bone formation and reconstruction. In H J J Blackwood
(ed):Bone and Tooth Symposium. New York: MacMilian
Company, pp. 21-23.
Frost, HM (1969) Tetracycline-based histological analysis
of hone remodeling. Calc. Tiss. Res. 3.211-327.
Kerley, ER (1965) The microscopic determination of age in
human hone. Am. J. Phys. Anthrop. 23149-164,
Kerley. ER, and Ubelaker, DH (1978) Revisions in the
microscopic method of estimating age a t death in human
cortical
~ bone. Am.
~ J. Phys.
~ Anthrop.
~ 49:545-546.
Ubelaker. DH 11977) Problems of the microscopic deter
mination of age a t death. Paper presented to the 29th annual meeting of the American Academy of Forensic
Sciences, San Diego, California.
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