Left-right discrimination in medicine
BMJ 2008; 337 doi: https://doi.org/10.1136/bmj.a2906 (Published 16 December 2008) Cite this as: BMJ 2008;337:a2906
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Editor
I agree with Professor McManus about the confusion left and right
causes (1). However, more amazing is the widespread existence of
handedness or chirality in nature. Sidedness is not just unique to humans
or animals. It is a phenomenon found at many levels in nature. For
example, it is found at molecular level. Different molecules spin in
different directions. All amino acids in proteins are left-handed, while
all sugars in DNA and RNA, and in the metabolic pathways, are right-
handed. A change in the sidedness of these molecules has profound effects
on the characteristics of these molecules. This is well illustrated by the
example of artificially synthesized sugars consisting of only left
spinning molecules. These sugars, although similar to the naturally
occurring right spinning sugars in their chemical structure, are
completely rejected by the human digestive system and are not absorbed at
all (2). Why this handedness in sugar molecules is mystifying. How does
the digestive system sense this change in chirality is even more
perplexing. Similarly a single wrong-handed amino acid would disrupt the
shape of á-helix in proteins that is crucial for the catalytic function of
proteins and therefore would not be able to support life. Why life on
earth uses only L-amino acids for protein synthesis and not their D mirror
images?
Plant kingdom also exhibits sidedness. The honeysuckle winds around
its support in a left handed helix while the bindweed prefers winding from
right to left (2,3) . Why one plant has the propensity to prefer one side
over the other begs belief. And why limonene, a compound found both in
lemons and oranges has a spin opposite to each other in the two fruits. It
is astounding that the spin of limonene in lemons is always right spinning
while in oranges it is always left spinning, both have same chemical and
physical properties except that one smells like lemon and the other like
oranges (2,3).
Sidedness is also seen in bacteria and at the subatomic level. For
example, Bacillus subtilis, usually forms right-handed spiral colonies.
And whilst neutrinos always spin left, anti-neutrinos spin in the opposite
direction, to the right (2,3).
There is still a great deal of prejudice against left handedness in
certain societies. In a study in Malawi, 87.6% of the responders indicated
that left-handers should be forced to change the hand (4). The most common
reason for this prejudice is the assumption that the left hand is less
skilled and less powerful than the right.
We do not know the mystery of sidedness and the significance of it.
The origin of this handedness is a complete mystery to evolutionists.
Scientists argue about the origins of chiral asymmetry, did it arise
before or after the birth of the first cell. It seems sidedness has much
more importance than we have realized. Future research will hopefully give
answers to some of the fundamental questions about the significance of
chirality and what dictates the propensity of being right or left
sidedness, not only in humans and animals but also at every level of
material existence.
References:
1-McManus C. Left-right discrimination in medicine. BMJ 2008; 337:
1426-7.
2-Chirality or sidedness in nature. In: Ahmad MT. Revelation,
Rationality, Knowledge and Truth. Islam International Publications Ltd.
1998: pp. 411-22.
3-Hegstrom RA, Kondepudi DK. The handedness of the universe.
Scientific American 1990; 262(1): 108-15.
4-Zverev Y P. Cultural and environmental pressure against left-hand
preference in urban and semi-urban Malawi. Brain Cognition 2006; 60(3):
295-303.
Competing interests:
None declared
Competing interests: No competing interests
The editorial by Chris McManus on handedness and the article on left-
right discrimination in surgical trainees in the Christmas Issue of the
BMJ raise important questions that extend beyond the use of surgical
instruments 1,2. Spatial awareness requires binocular vision but most
surgeons have a dominant eye too. The operating microscope is set to the
dominant eye and, if the teaching arm or camera is set on the opposite
side, the operating field may not be in the centre. Modern microscopes
get around this by taking the teaching image from above the beam splitter.
If monocular endoscopes are used, crossed laterality may not be a problem
but it may in other situations. The ENT clinic in the UK is set up for
right eye dominated and right handed individuals. Those individuals who
are left eye dominated but right handed have a problem, as do those who
are left eye and hand dominant.
Teaching surgery to right-handed trainees who want to stand on the same
side of the operating table as the right-handed surgeon may be best when
using the endoscope but in other situations a left hander standing on the
opposite side may allow better access for the trainee or assistant.
Individuals have a dominant ear and this may be a problem for some
patients particularly children with unilateral glue ear where a unilateral
problem may cause disproportionate difficulties. Usage is not always a
sign of laterality as Jimi Hendrix wrote with his right hand but played
the guitar left-handedly: as demonstrated in the image of the guitar
player in the same issue of the BMJ.
The debate must extend beyond the confines of handedness to get to grips
with hand-eye coordination and laterality. Let us leave the term
dexterity out of it!
References:
1. McManus C. Left-right discrimination in medicine: Are left handed
people the last great neglected minority? BMJ. 2008; 337: 1426-7.
2. Leiske B. The left-handed surgical trainee. BMJ. 2008; 337: 1476.
Competing interests:
left-handed surgeon with a dominant right eye, ear and foot who has a left-handed sister, brother-in-law, daughter and granddaughter. All the other members of the other members of the family are right handed.
Competing interests: No competing interests
As a right handed person, I was horrified to attend A Basic Surgical
skills course last month. I was informed that all knots, in accordance
with the royal college of surgeons, would be taught using the single left
hand technique. O no! I was never gifted in the scouts knot tying
department - using right hand or both hands so this news filled me with
dread. I blundered my way through the first session by day 3 had mastered
being a leftie. The same applied to using surgical instruments. At least
now I can be happy that if my right arm is indisposed the poor artery
needing tying will not be left unattended!
A similar problem occurs when I play one of my favourite sports -
cricket. As a wicketkeeper I dread the sight of an incoming leftie. Not
because I fear they may be the next Brian Lara but because bowlers have
this talent to bowl shocking spells against left hander’s. Wides, leg side
balls, no balls at all! They all come thick and fast and coupled with the
inconsiderate batsman who due to the position of a left hander, requires
me to stand in a different position, really does spoil my day! My father
is a left hander and was given this stern advice from my grandfather as a
boy when learning to play golf. There were no left handed clubs available
to use. My grandfathers simple answer to the problem. Don't be awkward and
just hit them right handed. Or if that doesn't work turn the club
around!!!
In a world of equal opportunity who knows where this latest article
defending the lefties will end? Age discrimination already exists. Maybe
the call should now be made for leftie discrimination??? Until then I will
continue to despise tying knots left handed and curse the left handed
batsmen that spoil my Sunday afternoon!
Competing interests:
I am right handed and find left handers an irritation
Competing interests: No competing interests
What are the learning needs of lefthanders?
What, really, are "the needs of lefthanders"? McManus sympathises
with us lefthanders for whom special digital cameras are not produced.
Despite being "gauche" and "sinister", rather than "dextrous", since
birth, I had never until now considered myself camera-disadvantaged. And
when this Christmas my family decided I should no longer be the sole adult
member of my country's electorate not able to use a mobile phone (!), and
gave me one, I began to learn the new skill of text-typing with my right
thumb. I did not think of special "left-hander" ways of using it- no more
than when I use a knife and fork, drive a car, or play the viola. In all
these cases, I came to use a piece of equipment - cutlery, car, fiddle,
phone - with handedness inbuilt, and learnt to work it. The only things I
do markedly better lefthandedly are to write with a pen or pencil, to
throw a ball accurately, and to kick a football. In each case I imagine
that a natural left preference made me begin on the left, and thereafter I
invested in the learning curve on that sidedness.
The interesting psychological research - has it been done? - would be
to study times and performances for learning new skills that involve
handedness, in ipsi- against contralateral handers. Are there left-
handers who can learn to use a novel "right-handed" camera, or musical
instrument,etc, as fast as right-handers? And others who can't? And if so,
in what other ways do these two groups differ?
Competing interests:
None declared
Competing interests: No competing interests