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Clinical Anatomy 14:254 –257 (2001)
Intercondylar Shelf Angle in Adult Black
Malawian Subjects
P.S. IGBIGBI,* B.C. MSAMATI,
AND
T.M. NG’AMBI
Department of Anatomy, College of Medicine, University of Malawi, Blantyre 3, Malawi
In this study, we determined the intercondylar shelf angle of the femur in adult black
Malawian subjects as measured in lateral radiographs of the knee joint. A total of 856
radiographs were used: 464 from men and 392 from women, aged 18 –70 years. A goniometer
measured the intercondylar shelf angle at the intersection between Blumensaat’s line and a
line drawn along the edge of the distal third of the femur parallel to the posterior cortex of
the bone. The mean intercondylar shelf angle of 136.60° ⫾ 5.90° in Malawians of both sexes
was significantly different from 142.57° ⫾ 5.86° for American subjects (P ⬍ 0.001), as given
by Craig (1995, J. Forensic Sci. 40:777–782), but the level of statistical significance between
black Malawian females and black American females was at P ⬍ 0.01. Using the intercondylar shelf angle, 66.67% of male Malawians were correctly identified as such and 50.00%
of Malawians females as such. Eighty-three percent of males and 81.30% of females were
correctly identified as blacks. This angle has been shown to exhibit sexual dimorphism in
Malawian subjects. Its importance in forensic anthropology is stressed. Clin. Anat. 14:254 –257,
2001. © 2001 Wiley-Liss, Inc.
Key words: human knee; femur; racial variation; forensic anthropology
INTRODUCTION
Different methods exist for analyzing and describing human variation, but few of these utilize the
femur to differentiate race (Stewart, 1962; Lavelle,
1973; Farrally and Moore, 1975; Gilbert, 1976; Craig,
1995). Still fewer methods use metric analysis of the
intercondylar notch to distinguish race (Baker et al.,
1990).
The intercondylar notch of the femur is U-shaped,
lies at the distal end of the femur, and separates two
large oblong condyles that project posteriorly (Moore,
1992). The intercondylar shelf is a line of dense cortical bone that forms the “roof” of the intercondylar
notch. This area is best seen in a sagittal section of the
femur and it is represented as a relatively radiopaque
line in a lateral radiograph of the knee (Fig. 1). Blumensaat (1938) first described the line and it is now
named for him; it marks the normal position of the
patella if the knee is flexed at 30° (Carson et al., 1984).
The intercondylar shelf angle is the angle formed at
the intersection of Blumensaat’s line and a line drawn
parallel to the posterior cortex of the femur (Fig. 2).
This angle shows a relatively consistent and statistically significant difference between American whites
and blacks (Craig, 1995).
©
2001 Wiley-Liss, Inc.
In a study using skeletal samples, Baker et al.
(1990) showed differences in height of the intercondylar notch between whites and blacks. This difference was shown to affect the intercondylar shelf angle
in such a way that the more acute the angle was, the
higher the notch, whereas a more obtuse angle indicated a lower notch (Craig, 1995). These investigators
have further demonstrated that this angle exhibits
racial variation, and hence its importance. The angle is
easily measured and its variation is independent of the
size of the femur, of the effect of arthritis in the notch,
or of trauma to the articular surface. Moreover, the
method is noninvasive, and can be applied to both
skeletal material and to femora with intact soft tissue.
The angle can be measured in fragmented femora,
and only a single measurement is necessary (Craig,
1995).
Despite the importance of this angle in forensic
anthropology, there are few published reports, and
they refer only to American whites and blacks. There
*Correspondence to: P.S. Igbigbi, Department of Anatomy, College of Medicine, University of Malawi, Private Bag 360 Chichiri,
Blantyre 3, Malawi. E-mail: [email protected]
Received 15 September 1999; Revised 6 December 1999
Intercondylar Shelf Angle in Malawians
255
Fig. 1. Roentgenogram indicating the radiopaque roof of the
intercondylar notch.
Fig. 2. Roentgenogram illustrating the intercondylar shelf angle
(A). B, Blumensaat’s line; P, A line drawn parallel to the edge of the
cortex of the posterior distal third of femur.
are no reports on the angle in Malawians, nor, indeed,
in other African subjects. This study therefore provides baseline data for indigenous adult black subjects. These data will be useful in forensic anthropology because Malawi has both black and white people
in its population.
faced left, thereby reducing technical errors that occur
if the femur is not properly positioned. To position
the femur properly, the anterior aspect of the knee
must face left with the medial condyle facing upwards, away from the table, and then a true lateral
view will be closely approximated. In this position,
the knee is normally placed at 30° (Lusted and Keats,
1978). Only radiographs that met these conditions
were measured. A metal ruler was aligned with one
edge against the distal one-third of the femur parallel
to the posterior cortex of the bone, and a line was
drawn along the opposite edge of the ruler. The ruler
was then placed so that one edge went through Blumensaat’s line in a “best-fit” alignment. A second line
was then drawn along the edge. Blumensaat’s line is
the line drawn along the dome of the intercondylar
fossa, and an extension of this line anteriorly meets
the inferior pole of the patella (Fig. 2), provided the
knee is flexed at 30°. A goniometer was placed over
the intersection of these two lines and the interior
angle was measured (Fig. 2).
MATERIALS AND METHODS
Lateral radiographs of 856 individuals (464 men
and 392 women aged 18 –70 years) were examined.
The radiographs were collected from hospitals in all
three regions of the country: Queen Elizabeth,
Lilongwe, and Zomba Central Hospitals and Mzimba,
Rumphi, and Mchinji district hospitals. All the radiographs used were known to belong to indigenous
black Malawians.
Either the left or right knee was used to measure
the intercondylar shelf angle from each roentgenogram. Each radiograph was placed on a light box and
positioned so that the anterior aspect of the knee
256
Igbigbi et al.
TABLE 1. Characteristics of Intercondylar Shelf Angle in Adult Black
Malawians
Intercondylar shelf angle (degrees)
Range
Mean and SD
Men
(n ⫽ 464)
Women
(n ⫽ 392)
Both
(n ⫽ 856)
130–143
135.09 ⫾ 4.81
125–153
138.68 ⫾ 6.82
125–153
136.60 ⫾ 5.90
TABLE 2. Means and SD of Intercondylar
Shelf Angle (Degrees) by Race and Sex
TABLE 3. Comparison of Intercondylar Shelf Angles in
Various Groups of American and Malawian Subjects
All by race
Comparison between
American blacksa
American whitesa
Black Malawiansb
n
183
240
856
Mean
137.83
146.18
136.60
SD
4.18
4.29
5.90
All by sex
American womena
American mena
Black Malawian womenb
Black Malawian menb
188
235
392
464
142.59
142.55
138.68
135.09
6.31
5.61
6.82
4.81
Women by race
Black American womena
White American womena
Black Malawian womenb
80
108
392
137.16
146.60
138.68
4.14
4.31
6.82
Men by race
Black American mena
White American mena
Black Malawian menb
103
132
464
138.35
145.83
135.09
4.16
4.25
4.81
Malawian men and women
American whites and blacks
American blacks and Malawian blacks
American whites and Malawian blacks
American women and American men
American women and black Malawian
women
American men and black Malawian men
Black American women and white
American women
Black Malawian women and black
American women
Black American men and white
American men
Black American men and Black
Malawian men
White American men and Black
Malawian men
t values
P values
8.73
20.00
3.32
25.89
0.07
7.52
⬍0.001
⬍0.001
⬍0.001
⬍0.001
nsa
⬍0.001
17.34
15.53
⬍0.001
⬍0.001
2.62
⬍0.01
13.60
⬍0.001
6.64
⬍0.001
24.98
⬍0.001
a
a
Source, Craig (1995).
b
Source, present study.
A repeatability study was conducted in which the
three authors independently marked and measured
the angle on 50 radiographs, using the method described above. Each author measured each angle twice
to ensure accuracy.
The intercondylar shelf angle thus measured was
recorded together with the name, age, and sex of the
subject. The lines were erased from the radiographs
between each of the three author’s measurements. We
tested for interobserver error and the variation among
them averaged less than 1°.
Each radiograph was classified by sex and race
using Craig’s (1995) method. Those with an intercondylar angle of 137° or greater were classified as female
whereas those with an angle less than 137° were classified as male. Individuals with an angle of 142° or
greater were classified as white and those with an
angle of 141° or less were classified as black.
All results were analyzed using the SAS statistical
package for Windows 6.08 and are presented in Tables 1–3.
RESULTS
Table 1 shows the characteristics of the intercondylar shelf angle in the sample. The means and stan-
ns, not significant
dard deviations (SD) of intercondylar shelf angles by
race and sex of the subjects are presented in Table 2
and are compared with results from Craig (1995) in
Table 3.
Malawian women have a significantly higher intercondylar shelf angle than Malawian men (P ⬍ 0.001)
(Table 3). Table 3 also shows that most of the parameters were highly significantly different (P ⬍ 0.001)
and significantly different between black Malawian
and black American women (P ⬍ 0.01). There was,
however, no significant difference between the angles
in American men and women (P ⬎ 0.5). The results
also revealed that the sex of 66.67% (n ⫽ 309) of the
men and 50.00% (n ⫽ 196) of the women was correctly
identified. About 83% (82.50%, n ⫽ 706) of the entire
sample were correctly classified as black; and of these
706 individuals, 83.30% (n ⫽ 387) were correctly identified as men and 81.30% (n ⫽ 319) were correctly
identified as women.
DISCUSSION
We have shown that the intercondylar shelf angles
vary between men and women in this Malawian sample, being significantly greater in women. This is at
variance with American subjects, who showed no significant difference between men and women (P ⬎ 0.5)
Intercondylar Shelf Angle in Malawians
(Craig, 1995). The lower limb angles represented by
femoral neck-shaft and anatomic angles do exhibit
sexual dimorphism (Igbigbi and Kwatampora, 1997),
but the angles previously reported were normally
larger in men than in women. The differences between the American series and ours might arise from
environmental and dietary factors.
It has also been shown that intercondylar shelf
angles vary between races. In a study on American
whites and blacks, Craig (1995) introduced a new
method to determine race from measuring intercondylar shelf angles. He showed that it was relatively
easy to do once the landmarks had been located and
marked, that it could be used for fragmented femora,
and that it gave reproducible results. Furthermore, the
angle is not affected by arthritis, articular trauma or by
size, length, or overall curvature of the femur (Craig,
1995).
Previous studies have shown that the femora of
blacks are generally longer and have less anterior curvature than those of whites (Trotter and Gleser, 1952;
Stewart, 1962). Whites have more anterior bowing
than blacks but this has not been found to affect the
measurement of the intercondylar shelf angle (Craig,
1995). If the curvature of the femur were to be included in the intercondylar shelf angle analysis, it
would further increase the differences between the
races. Craig (1995) argued that this is because a more
anterior bow, typical of whites, will create a more
acute angle whereas in blacks with less anterior bowing, the angle will be more obtuse.
The method employed here was based on the measurement of lateral radiographs of the knees of living
subjects. In a clinical situation, the leg and knee can
be positioned in such a way as to control rotation of
the entire limb and a “true lateral” radiograph can be
taken; the position of Blumensaat’s line will be consistently correct (Craig, 1995) and the method can be
applied. The only problem with this method is with
individuals whose intercondylar shelf angles are close
to or overlap the watersheds of 137° for sex and 141–
142° for race. This problem, however, is a familiar one
in forensic identification (Craig, 1995). Nevertheless,
measurements of the intercondylar shelf angle were
used to determine sex and race in the present study.
We have demonstrated that the method gives a higher
257
determination of race than of sex. This finding confirms the reports on whites and blacks (Trotter and
Gleser, 1952; Stewart, 1962; Craig, 1995). Its usefulness in forensic anthropology cannot be underestimated especially in mixed societies and populations.
We recommend this method for determining race
in mixed populations. Its usefulness is unquestionable
in poor developing countries like Malawi where forensic anthropology is lacking or is a luxury. Since mixed
societies have become an important ingredient of population dynamics in Africa, the method would indeed
be invaluable for medico-legal cases in Africa and
other developing countries.
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