LATERAL ASYMMETRY OF HUMAN LONG BONES

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Lateral asymmetry of human long bones
Variability and Evolution, 2001, Vol. 9: 19–32
19
TONKA ÈUK, PETRA LEBEN-SELJAK, MARIJA ŠTEFANÈIÈ
University of Ljubljana, Department of Biology, Biotechnical Faculty,
Veèna pot 111, SI-1000 Ljubljana, Slovenia
LATERAL ASYMMETRY OF HUMAN LONG BONES
ÈUK T., LEBEN-SELJAK P., ŠTEFANÈIÈ M. 2001. Lateral asymmetry of human long bones. Variability and
Evolution, Vol. 9: 19–32, Tabs. 2, Figs. 4. Adam Mickiewicz University, Faculty of Biology, Institute
of Anthropology, Poznañ.
Abstract: Based on the anthropometric data of long bones of 26 female and 16 male
medieval skeletons from the necropolis Središèe by the Drava river in Slovenia an
analysis of lateral asymmetry was performed. We determined the degree of direct and
standardized asymmetry of specific morphological characteristics in individual long
bones and tried to deduct the right- or left-handedness of the individual. Our results
indicate directed asymmetry which is more pronounced in the upper extremities. The
most asymmetric bone is humerus, reflecting the hand preference. The dominant leg is
expressed by the stronger tibia usually on the opposite side of the dominant arm. The
stronger development of the left femur as supportive limb is characteristic of both
right- and left-handers.
Key words: anthropometry, bilateral asymmetry, long bones, medieval skeletons
Introduction
During bone dynamic development we discern growth in both length and
diameter. Growth in diameter is dependent on periosteal ossification while growth
in length depends on endochondral ossification of the epiphyseal plate. Both localized
and general factors are present. Of the general ones the best known are genetic
factors, the influence of availability of minerals and vitamins, and hormonal
20
T. Èuk, P. Leben-Seljak, M. Štefanèiè
regulation. But localized factors, too, play a role: an adequate and uninterrupted
blood flow and mechanical stresses on the bone (Ruszowski, Orliè 1977). In
humans lateral asymmetry is wellknown. Current studies have confirmed the long
held thesis that in the majority of people, in about 90%, the right arm is more
developed than the left, while in the legs it is just the reverse, although less marked:
55% to 75% of people have a stronger left leg. This limb dominance only means
an advantage in its use as shown by stronger musculature. The long bones are
dependent on different degrees of stress and thus morphologically are bilaterally
asymmetrical. The degree of asymmetry reflects the degree of force exerted onto
the right or left limb, while the particular bone site showing asymmetry indicates
the kind of force exerted.
Studies of the degree of asymmetry in human long bones began on the nineteenth
century. The most frequently used dimensions were the total length and weight
measured both in skeletons and living people, and in archeological collections.
Although data were gathered in different groups of people living in different
circumstances all results agree and demonstrate that bilateral asymmetry is more
marked in arm bones than leg bones and that on average right arm bones are
longer by 1% to 3% and heavier by 2% to 4% than left limb bones. A few studies
also mention that the bones of the left leg, particularly the femur, are on average
longer and heavier than on the right but by less than 1%. The greater dimensions
of the dominant arm were also confirmed by studies where they tested the link
between increased activity and greater muscle mass or an increase in the mineral
values of the bones. Thus, it seems that directional asymmetry of the long bones
may be caused by local factors, particularly mechanical forces (Ruff, Jones 1981).
Detailed statement about skeletal indicators of handedness was published recently
(Steele 2000).
Steel and Mays (1995) tried to answer the questions of asymmetrical long bone
growth. Their measurements of the maximal length of the humerus, radius, and
ulna in a series of 271 skeletons from the medieval osteologic collection in Wharram
Percy in Yorkshire confirmed the presence of oriented asymmetry in arm bone
length. The proportion of people with longer right or left long arm bones in this
medieval population agreed with the proportion of right or left handers in modern
populations. They determined that right- or left-handedness are the main causes of
oriented asymmetry as they determine the use and thus the greater mechanical stress
of the dominant arm. This could also be attributed to hidden genetic or hormonal
factors, but the authors decry this thesis by the conclusion that asymmetry appears
only when the limbs are asymmetrically mechanically loaded and increases with
a child’s age.
Authors who have studied lateral asymmetry of the legs have confirmed that the
left leg is heavier than the right but the results of differences in length are not
uniform (Latimer, Lowrance 1965; Singh 1970). Ruff and Hayes studied the
asymmetry in the shape of the femur. They determined that the left femur is stronger,
Lateral asymmetry of human long bones
21
particularly in women but they did not find a difference in length (Ruff 1992).
Macho (1991) was interested in how much bilateral asymmetry we can notice by
measuring whole femurs. He chose those measurements most likely to be influenced
by different forces. After statistical analysis on 166 South African Negroes thigh
bones, he came to the conclusion that on average the left leg was stronger and in
most people, regardless of right- or left-handedness, was the supporting leg while
the right was used for other functions.
In this study, performed by anthropometric methods in a long bone series of
medieval skeletons from Središèe by the Drava river, we tried to determine:
1. the degree of asymmetry of specific morphologic characteristics in individual
long bones,
2. whether may we deduct the right- or left-handedness of the individual on the
basis of this material.
Materials and methods
The sample
The sample consists of 248 more or less preserved skeletons from the tenth to
the fifteenth centuries exhumed in 1993 and 1994 in Središèe by the Drava river,
NE Slovenia. For the analysis we chose adult skeletons with preserved upper arm
bones and at least one pair of another long bones. In all, we included 42 skeletons,
26 female and 16 male. Skeletal sex was determined by standard anthropological
methods (Recommendations 1980).
Methods
To gain as much metric data as possible and to ensure that all parts of bones
were represented, we chose those measurements according to Martin and Saller
(1957) as well as 3 of our own. The maximum circumference of the humeral
shaft (H-MCD) was measured with a measuring tape at the point of greatest
circumference, approximately in the middle of the shaft or on the deltoid tuberosity.
The bitubercular width of the humerus (H-BTW) was measured with a sliding
caliper between the highest points of the major and minor tubercles. The sagittal
diameter of the distal epiphysis of the ulna (U-SDD) was measured with a sliding
caliper at the widest part of the epiphysis in the saggital plane. All measurements
are given in centimeters with a precision of one millimeter as allowed by the
instruments.
The degree of direct asymmetry A for every measurement in individual skeletons
was expressed as the difference between values in paired bones. Direct asymmetry
is given in the same values as the measurements, that is in cm. It also told us how
22
T. Èuk, P. Leben-Seljak, M. Štefanèiè
many units one bone differed from the other and thus gave us the direction of
asymmetry:
A=D–L
(A, the degree of direct asymmetry; D, value of the right bone; L, value of the left
bone).
The degree of asymmetry was standardized by the mean values of measurements
on the right and left sides. This standardized degree of asymmetry SA represented
a ratio and thus had no units but made possible comparisons of any size regardless
of the specific bone or the size of the skeleton. Just as direct asymmetry it also
gave the direction of the asymmetry.
SA =
(D – L)
 D+ L


 2 
⋅ 1000
The statistical analysis was performed for individual data. The statistical results
were checked by the two-way Student’s t-test. All analyses were done in Excel 7.0
for Windows 97. Because of the small number of paired bones, we did not separate
them by sexes, following Steel and Mays (1995) who had found no differences in
the degree of lateral asymmetry in the sexes, at least for lengths of the upper
extremities.
Results
Tables 1 and 2 show the results of the analysis of metric data of the long bones
and the standardized degree of asymmetry The results confirm the presence of
oriented asymmetry more prominent in the arms than the legs. The average lateral
asymmetry in the arms was to the right, in the legs to the left. By far the most
asymmetric bone was the humerus where almost all the parameters were highly
significant but particularly the minimal circumference of the shaft, the bitubercular
width, and the maximal length. The total humeral length, the projection of the upper
arm, only showed a smaller degree of asymmetry, yet it was still statistically significant.
In the lower extremities only 2 parameters were significant: the length and the central
circumference of the femur.
These results are the average of a series where all preserved paired bones were
studied. It is known that left-handers have a contrary direction of their asymmetry
to right-handers in their arm bones, particularly the humerus, and this lowers average
values. Because of this, we excluded „probable left-handers” and analysed them
separately. Our criterion for exclusion was the direction of asymmetry in the most
asymmetric bone, the humerus. This decision, of course, was somewhat hazardous
as it was based only on the expression of anthropometric characteristics but the
difference in the 2 groups was so large that it seemed reasonable. We add that the
23
Lateral asymmetry of human long bones
percentage of left handers does reflect the actual numbers in the population, 15%,
but in such a small series as ours was represented only by 5 subjects.
We determined that the graphs of right-handers were very similar to the entire
average population. In the arm bones the degree of right directed asymmetry was
Table 1
The direction of lateral asymmetry of long bones
Measure
Direction of lateral asymmetry
N*
R>L
[%]
R=L
[%]
R<L
[%]
Humerus
H-1
H-2
H-4
H-7
H-11
H-MCD
H-BTW
30
26
33
42
37
35
22
26
21
10
29
13
19
13
87
81
30
69
35
54
59
1
1
18
11
23
13
8
3
4
55
26
62
37
36
3
4
5
2
1
3
1
10
15
15
5
3
9
5
Radius
R-1
R-2
R-3
R-5.1
R-5.6
23
26
37
32
26
17
19
18
8
11
74
73
49
25
42
2
5
13
20
15
9
19
35
63
58
4
2
6
4
0
17
8
16
13
0
Ulna
U-1
U-2
U-3
U-6
U-SDD
8
17
27
29
11
6
13
13
7
5
75
76
48
24
45
1
3
10
18
5
13
18
37
62
45
1
1
4
4
1
13
6
15
14
9
Femur
F-1
F-2
F-8
F-9
F-10
F-18
F-19
F-21
32
32
33
33
33
35
33
28
9
8
7
7
5
9
7
6
28
25
21
21
15
26
21
21
4
3
8
13
20
17
16
18
13
9
24
39
61
49
48
64
19
21
18
13
8
9
10
4
59
66
55
39
24
26
30
14
Tibia
T-1
T-1a
T-3
T-6
T-8a
T-9a
T-10b
20
20
17
19
28
28
28
6
10
4
3
9
9
12
30
50
24
16
32
32
43
3
0
10
10
9
7
9
15
0
59
53
32
25
32
11
10
3
6
10
12
7
55
50
18
32
36
43
25
* Number of examined bone pairs
24
T. Èuk, P. Leben-Seljak, M. Štefanèiè
Table 2
The degree of lateral asymmetry of long bones
Measure
Direct asymmetry
Standardised asymmetry
A
SDA
t-test
p
SA
SDSA
t-test
p
Humerus
H-1
H-2
H-4
H-7
H-11
H-MCD
H-BTW
0.377
0.300
0.024
0.102
0.035
0.077
0.073
0.362
0.356
0.087
0.107
0.072
0.109
0.088
0.000
0.000
0.118
0.000
0.005
0.000
0.001
***
***
12.120
9.909
4.113
18.663
15.316
11.089
17.202
11.391
11.407
14.570
18.981
29.645
15.688
20.692
0.000
0.000
0.115
0.000
0.003
0.000
0.001
***
***
Radius
R-1
R-2
R-3
R-5.1
R-5.6
0.152
0.162
0.049
0.016
0.046
0.237
0.248
0.119
0.068
0.058
0.006
0.003
0.018
0.201
0.000
**
**
*
6.517
7.259
13.679
7.124
15.677
10.178
11.167
32.553
32.388
20.474
0.006
0.003
0.015
0.223
0.001
**
**
*
Ulna
U-1
U-2
U-3
U-6
U-SDD
0.250
0.206
0.033
0.007
0.045
0.302
0.301
0.073
0.070
0.082
0.052
0.012
0.026
0.602
0.096
10.430
9.647
10.350
4.454
22.818
12.171
14.294
22.361
32.226
40.714
0.046
0.013
0.024
0.463
0.093
*
*
*
Femur
F-1
F-2
F-8
F-9
F-10
F-18
F-19
F-21
–0.166
–0.169
–0.061
–0.012
–0.015
0.000
–0.012
0.011
0.472
0.403
0.150
0.099
0.076
0.084
0.078
0.069
0.056
0.024
0.027
0.488
0.258
1.000
0.379
0.415
–3.900
–3.970
–7.357
–3.603
–5.783
–0.450
–3.391
1.696
10.598
9.043
18.125
32.930
31.612
18.057
17.268
9.345
0.046
0.019
0.026
0.534
0.301
0.884
0.268
0.345
*
*
*
Tibia
T-1
T-1a
T-3
T–6
T-8a
T-9a
T-10b
–0.150
–0.035
0.006
–0.011
–0.011
–0.018
0.025
0.408
0.416
0.066
0.099
0.117
0.098
0.129
0.117
0.711
0.718
0.650
0.631
0.345
0.316
–4.106
–0.729
0.790
–2.114
–3.975
–6.485
3.522
11.239
11.318
9.318
19.137
38.973
42.637
18.817
0.119
0.776
0.731
0.636
0.594
0.428
0.331
***
**
***
***
***
*
*
*
*
***
**
***
***
***
* p < 0.05; ** p < 0.01; *** p < 0.001
even higher than the average, the right handed dominance was even more expressed.
The graph demonstrating the standardized lateral asymmetry of the left humerus is
almost a mirror image of the right-handed graph, only the bitubercular width and
the maximal shaft circumference were also greater on the right bone (Fig. 1). The
25
Lateral asymmetry of human long bones
RIGHT-HANDERS
17,47
H-BTW
11,16
H-MCD
18,27
H-11
21,99
H-7
6,05
H-4
12,53
H-2
14,79
H-1
–20
–15
–10
–5
0
5
10
15
20
25
20
25
Degree of standardized asymmetry
LEFT-HANDERS
H-BTW
15,50
H-MCD
10,37
H-11
–9,08
H-7
–5,96
H-4
–6,71
H-2
–10,16
H-1
–11,93
–20
–15
–10
–5
0
5
10
15
Degree of standardized asymmetry
Fig. 1. The average degree of standardized asymmetry of humerus
26
T. Èuk, P. Leben-Seljak, M. Štefanèiè
RIGHT-HANDERS
16,98
R-5,6
7,78
R-5,1
14,78
R-3
6,95
R-2
7,30
R-1
–-20
–15
–10
–5
0
5
10
15
20
25
15
20
25
Degree of standardized asymmetry
LEFT-HANDERS
0,00
R-5,6
0,83
R-5,1
R-3
1,16
R-2
9,61
R-1
–1,69
–20
–15
–10
–5
0
5
10
Degree of standardized asymmetry
Fig. 2. The average degree of standardized asymmetry of radius
27
Lateral asymmetry of human long bones
RIGHT-HANDERS
2,03
F-21
–3,04
F-19
–0,44
F-18
–5,46
F-10
–5,19
F-9
–8,37
F-8
F-2
–3,42
F-1
–3,35
–20
–15
–10
–5
0
5
10
15
20
25
15
20
25
Degree of standardized asymmetry
LEFT-HANDERS
F-21
–0,29
F-19
–5,92
F-18
–0,55
F-10
–8,12
F-9
7,93
0,00
F-8
F-2
–7,82
F-1
–7,75
–20
–15
–10
–5
0
5
10
Degree of standardized asymmetry
Fig. 3. The average degree of standardized asymmetry of femur
28
T. Èuk, P. Leben-Seljak, M. Štefanèiè
RIGHT-HANDERS
2,40
T-10b
–4,86
T-9a
–7,59
T-8a
–5,06
T-6
0,05
T-3
–2,33
T-1a
–6,35
T-1
–20
–15
–10
–5
0
5
10
15
20
25
Degree of standardized asymmetry
LEFT-HANDERS
T-10b
10,23
T-9a
–16,21
T-8a
17,70
T-6
8,93
T-3
6,37
T-1a
5,69
T-1
4,88
–20
–15
–10
–5
0
5
10
15
Degree of standardized asymmetry
Fig. 4. The average degree of standardized asymmetry of tibia
20
25
Lateral asymmetry of human long bones
29
left-handed radius showed a much lesser degree of asymmetry but, except for
maximal lengths, was expressed as favouring the right (Fig. 2). Both right- and left-handers had a stronger left femur, only the transverse diameter of the diaphysis
was greater on the right in left-handers (Fig. 3). Right-handers had a longer and
stronger left tibia while left-handers were stronger on the right with the exception
of the shaft transverse diameter (Fig. 4).
Discussion
Our results confirm the findings of other authors that lateral asymmetry is
directional asymmetry, that in the arm bones particularly the humerus was much
more prominently expressed that in the lower limbs.
In all long bones the minimal circumference and shaft width were more
asymmetric than the maximal bone length. Steele and Mays (1995) found that
asymmetry in humeral length was markedly smaller than the lateral differences in
the strength of compression that in the modern population is 6–8%. They cite that
other authors had proved that there is a greater degree of asymmetry in the shaft
circumference coinsiding with differences in the strength of arm compression. In
our sample the degree of lateral asymmetry in diameters was smaller than the
differences in hand compression (the difference in the humeral minimal circumference
was 2.1%) but was greater than the degree of asymmetry in the length of the bone.
The length difference between the right and left was 1.4%, equal to that found by
Steele and Mays (1995). We think that this is a consequence of length growth
stopping between 18 and 25 years of age while width increases under biomechanical
factors during the life span. Steele and Mays also see another explanation; the
consequence of a compromise between the effect of asymmetry of strength in
potentiated use of the dominant hand and the effect of antagonistic muscles forces
with coordination of both hands.
We found that the proximal epiphysis of humerus was more asymmetric than
the distal one. The reverse held true for the forearm bones where the asymmetry
was greatest distally. It is apparent that the wrist and shoulder have greater
asymmetric stresses than the elbow.
The leg bones showed a reverse direction of asymmetry from the arm bones
and the degree of asymmetry was lesser. The sagittal diameter of the femur was
more asymmetric towards the left, meaning a greater vertical flattening of the head
and thus a greater stress on the bone. The left femur was obviously stronger, all
measurements of the diaphysis were larger and longer. These increased dimensions
on the left argue that it is the supporting side. The exception is the greater epicondilar
width on the right femur, a fact that Macho (1991) explains as a consequence of
the greater shearing forces in the knee as compared to the nondominant leg. In the
tibia the greatest average degree of asymmetry is shown by the transverse and
30
T. Èuk, P. Leben-Seljak, M. Štefanèiè
sagittal diameter of the diaphysis. This did not surprise us: most of the muscle
insertions are here. But as standard deviations in all measurements are high, the
lateral differences could not be proven statistically. It is interesting that results of
analysis of Old Slav long bones from Slovakia gave a similar result even though
Avenariova (1971) did not demonstrate asymmetry in any other studied bone. This
is probably due to the fact that average asymmetry for all sizes was considered to
be the difference between the averages of left and right bones, which is not
a reflection of the actual differences in individual samples.
The separation of right-handers from left-handers confirmed our expectations in
the arm bones. The degree of right handed asymmetry of the humerus and radius in
right-handers was even more potentiated. Left-handers had a longer and distally
stronger humerus. It is interesting that bitubercular width and the maximal
circumference were stronger in left-handers on the right humerus. Both these sites
are at the proximal end of the humeral diaphysis where the abductors insert (the
deltoid, supraspinatus, infraspinatus muscles) and the inner rotator (subscapular
muscle) of the shoulder. Obviously these left-handers did physical work with their
right arms.
Our results also showed differences in the degree of asymmetry in bones of the
lower extremities which were particularly interesting as we have not found similar
data in the literature. In general it is believed that people develop transverse asymmetry,
meaning that right-handers have better developed right arms and left legs with the
reverse in left-handers (Ruff, Jones 1981). One also finds the thesis that the left leg
is supportive without regard to right- or left-handedness while the right has other
functions, for example kicking (Singh 1970; Plato et al. 1985; Macho 1991). In the
majority of our skeletons, without regard to right- or left-handedness, the femurs
were stronger on the left as the average asymmetry is the same for both groups.
But in direct contrast the asymmetry in tibias was completely reversed. The length
as well as the circumference and width were larger in left-handers, only the transverse
shaft diameter showed a negative asymmetry. Thus the tibia, at least in our material,
demonstrated transverse asymmetry with the humerus. This means that right-handers
have a dominant left leg, left-handers a dominant right leg. On the other hand, from
the asymmetry of the femur we could deduce that regardless of right or left
handedness the supportive leg is usually on the left. A dominant leg therefore does
not always mean a supportive leg.
While studying the laterality of student legs, Škof (1991) actually decided the
dominant leg was the one used to push off during a start and as supportive the one
used to support oneself when thrown off balance. She found that it was not always
the same extremity. In most students the left leg was supportive without regard to
right or left handedness. She found no connection between the supportive and the
dominant leg as the degree of asymmetry was insignificant.
In view of these facts, we offer the thesis that the dominant leg lying opposite to
the dominant arm is expressed as a more developed tibia. In the majority of people
the supportive leg, without regard to hand dominance, is the left as shown by the
Lateral asymmetry of human long bones
31
greater development of the femurs in both right and left-handers. The dominance of
the lower extremity is less marked than that of the upper. But, of course, this must
be checked on a sample where we know both the dominant and the supportive
extremity.
Conclusions
Our sample population consisted of 248 skeletons from the burial ground at
Središèe by the Drava river representing the Slav population between the tenth and
fifteenth centuries. To analyze lateral asymmetry we could only use those skeletons
whose sex could be determined and which had both humeri and at least another pair
of long bones.There were 42 skeletons, 26 female and 16 male. Based on our analysis
of them, we determined the lateral asymmetry and tried to determine its cause.
Our conclusions can be summed up as:
1. Asymmetry is directed and more pronounced in the upper extremities than the
lower. This can be partly explained by the fact that we use our arms in countless
one-handed and both-handed ways. To a great degree the legs are intended for
walking, bipedal locomotion demanding the equal use of both extremities.
2. The most bilaterally asymmetric is the humerus, reflecting the hand preference.
We think that in skeletons with both preserved humeri we can determine right- or
left-handedness. The analysis has shown a major difference in asymmetry of those
skeletons with a better developed right humerus than the left and the latter represent
only 12% of our sample, a figure compatible with the presence of left-handers in
the population.
3. The dominant leg was expressed by the stronger tibia usually on the opposite
side of the dominant arm. Thus, right-handers usually have a dominant left leg,
left-handers a dominant right. Regardless of the hand preference and the dominant
leg, the left is the supportive limb as proven by the greater development of the left
leg in both right- and left-handers.
We have tried to elucidate asymmetry from several standpoints. All of these results
are valid for our sample population but, because of the small available archeological
sample, generalization is dangerous yet leaves the door open for further study.
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Latimer H.B., Lowrance E.W. 1965. Bilateral asymmetry in weight and in length of human bones. The
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