The male warrior hypothesis (MWH) is an evolutionary psychology hypothesis by Professor Mark van Vugt
which argues that human psychology has been shaped by between-group
competition and conflict. Specifically, the evolutionary history of
coalitional aggression between groups of men may have resulted in sex-specific differences in the way outgroups are perceived, creating ingroup vs. outgroup tendencies that are still observable today.
Overview
Violence and warfare
Violence and aggression
are universal across human societies, and have likely been features of
human behavior since prehistory. Archaeologists have found mass graves
dating to the late Pleistocene and early Holocene
that contain primarily male skeletons showing signs of blunt force
trauma, indicating the cause of death was by weapons used in combat.
Violence among humans occurs in distinct patterns, differing most obviously by sex. Ethnographic findings and modern crime
data indicate that the majority of violence is both perpetrated by and
targeted at males, and males are the most likely to be victims of
violence. This male-male pattern of violence has been observed so
repeatedly and in so many cultures that it may qualify as a human universal.
Tribal behavior
Men preparing for a raid.
Humans are a social species with a long history of living in tribal groups.
The psychological mechanisms that evolved to handle the complexities of
group living have also created heuristics for quickly categorizing
others as ingroup or outgroup members, with different behavioral
strategies for each: treat ingroup members (those in one’s own group)
favorably, and react to outgroup members (those who belong to a
different group) with fear and aggression. These tendencies arise with
little motivation, and have been provoked over superficial groups in lab
studies—for example, by showing paintings to participants and creating
groups based on which painting participants prefer.
The male warrior hypothesis suggests that the ease with which
individuals discriminate against others is an adaptation resulting from a
long history of being threatened by outgroup males, who are in
competition for resources.
Sex differences in parental investment
The
MWH argues that the sex differences in attitudes towards outgroup
members may be a result of the different reproductive strategies used by
males and females—specifically, the greater competition among males for
mates. In mammals, males and females have distinct reproductive
strategies based on the physiology of reproduction. Because females
gestate, birth, feed, and invest more overall resources in each of their
offspring, they are more selective with their mates but have greater
certainty of being able to reproduce.
Males, in contrast, can mate at a very low energetic cost once
they have found a partner, but are only able to attract a female if they
have physical or social characteristics that can be converted into
resources—e.g., territory, food resources, status, power, or
influence—or the strength and alliances to coerce females to mate.
As a result, there is typically much greater variability in the
reproductive success of males within a species and higher competition
among males for mates. The strongest, best adapted, and most powerful
males may have a harem, while less fit males never reproduce.
The
male warrior hypothesis predicts that because males may have
historically remained in the groups in which they were born rather than
moving away at adulthood (see patrilocality),
they have a higher overall relatedness to their group than the female
members, who would have moved to their new husbands’ group upon
marriage.
Males may have a stronger interest in defending their group, and will
be more likely to act aggressively towards outgroup males they encounter
who may be attempting to steal resources or weaken the group with
violence.
For men at risk of never finding a mate, the fitness benefit to
engaging in aggressive, violent behavior could outweigh the potential
costs of fightings, especially if fighting alongside a coalition.
Furthermore, the groups with more individuals who formed coalitions and
acted altruistically to in-group members but aggressively to outgroup
members would prosper.
Observational evidence/studies
Sex differences
Consistent with the expectations of the male warrior hypothesis, several studies have shown more ethnocentric and xenophobic
beliefs and behaviors among men (compared to women), including the more
frequent use of dehumanizing speech to describe outgroup members; stronger identification with their groups; greater cooperation when faced with competition from another group; a greater desire to engage in war when presented with images of attractive (but not unattractive) members of the opposite sex; greater overall rates of male-male competition and violence (as shown in violent crime and homicide statistics); and larger body size correlating with quicker anger responses.
Studies have also tested the responses of women to outgroups, and
have shown that women are most likely to fear outgroup males during the
periovulatory phase of the menstrual cycle, when fertility is at its peak.
Women also have more negative responses around peak fertility when the
males belong to an outgroup that the woman associates with physical
formidability, even if the group was constructed in the lab. Overall, women who feel most at risk of sexual coercion are more likely to fear outgroup males, which aligns with the predictions of the MWH.
Prepared learning studies
In studies of prepared learning,
conditioned fear responses to images of outgroup males were far more
difficult to extinguish than conditioned fear responses to outgroup
females or ingroup members of either sex, as measured by conductivity
tests of perspiration on the skin. These results held true whether the
participant was male or female.
Because the neural circuitry for fear responses are more developed
towards stimuli that have posed a larger threat for most of human
history (snakes and spiders, for example, which were dangers frequently
encountered by foragers),
these findings suggest that outgroup males may have been more of a
threat to physical safety than outgroup women or ingroup members,
supporting the male warrior hypothesis.
Sport matches
It
is hypothesized that sport began as a way for men to develop the skills
needed in primitive hunting and warfare, and later developed to act
primarily as a lek
where male athletes display and male spectators evaluate the qualities
of potential allies and rivals. This hypothesis is supported by the
observation that the most popular modern male sports require the skills
needed for success in male-male physical competition and primitive
hunting and warfare, and that champion male athletes obtain high status
and thereby reproductive opportunities in ways that parallel those
gained by successful primitive hunters and warriors.
There is evidence that male and female athletes generally differ in
their motivation in sports, specifically their competitiveness and risk
taking, in accordance with the spectator lek hypothesis.
The male warrior hypothesis proposes that men must engage in
maximally effective intra-group cooperation. Post-conflict affiliation
between opponents is proposed to facilitate future cooperation.
Regarding sports matches as a proxy for intra-group conflict, a study
found that unrelated human males are more predisposed than females to
invest in post-conflict affiliation that is expected to facilitate
future intra-group cooperation.
Non-human evidence
Coalitionary violence has also been observed in social species besides humans, including other primates. Chimpanzee (Pan troglodytes)
males demonstrate similar violent behavior: groups of males form
coalitions that patrol the borders of their territory and attack
neighboring bands. Chimpanzees also have patrilocal living patterns,
which aid with forming close coalitions, as all males are likely kin.
A study of 72 species of group-living mammals found that males
are more involved than females in inter-group conflict where male
fitness is limited by access to mates whereas female fitness is limited
by access to food and safety.
Emotional intelligence
(EI) involves using cognitive and emotional abilities to function in
interpersonal relationships, social groups as well as manage one's
emotional states. It consists of abilities such as social cognition, empathy and also reasoning about the emotions of others.
The literature finds women have higher emotional intelligence ability than men based on common ability tests such as the MSCEIT. Physiological measures and behavioral tests also support this finding.
Emotional intelligence
Emotional
intelligence (EI) involves using cognitive and emotional abilities to
function in interpersonal relationships, social groups as well as manage
one's emotional states. A person with high EI ability can perceive,
comprehend and express emotion accurately, and also has the ability to
access and generate feelings when needed to improve one's self and
relationships with others.
Women tend to score higher than men on measures of emotional intelligence, but gender stereotypes of men and women can affect how they express emotions.
The sex difference is small to moderate, somewhat inconsistent, and is
often influenced by the person's motivations or social environment.
Bosson et al. say "physiological measures of emotion and studies that
track people in their daily lives find no consistent sex differences in
the experience of emotion", which "suggests that women may amplify
certain emotional expressions, or men may suppress them".
Tests
Mayer-Salovey-Caruso Emotional Intelligence Test (MSCEIT)
The Mayer-Salovey-Caruso Emotional Intelligence Test (MSCEIT) is used to get emotional intelligence IQs (EIQ). It is the most widely used test for the ability of emotional intelligence (AEI), and is well-validated.
Much of the evidence for ability EI is based on the MSCEIT, partly
because it was the only test available to measure EI ability. It is also
the only omnibus test to measure all four branches of the EI ability model in one standardized assessment.
The area scores include experiential EIQ and strategic EIQ.
Experiential EIQ includes being able to recognize emotions to compare
them to other sensations and their connection to the thought process. Strategic EIQ focuses on the meaning behind emotions, how emotions affect relationships, and how to manage emotions.
After area scores, branch scores include four different sections:
perceiving emotions, using emotions, understanding emotions, and
managing emotions. Using these categories, the test analyzes people's ability to perform tasks and solve emotional problems or situations.
No self-perceived assessments are used in the test; it is an objective
assessment of a subject's ability to solve emotional problems.
A 2010 meta-analysis published in the Journal of Applied Psychology
by researchers Dana L. Joseph and Daniel A. Newman found that women
scored higher than men by around half a deviation, which amounts to 6–7
points difference.
Test of Emotional Intelligence (TIE)
The
Test of Emotional Intelligence (TIE) focuses on measuring perception
and comprehending emotions and the ability to use emotions and manage
them. It is considered to be the Polish equivalent of the MSCEIT.
Sex differences
Social cognition
Every day, people use social cognition
subconsciously, as it is part of most of modern society. Social
cognition is an important part of emotional Intelligence and
incorporates social skills such as processing facial expressions, body
language and other social stimulus.
A 2012 review published in the journal Neuropsychologia
found that men were more responsive to threatening cues while women
could express themselves more easily and were better at recognizing
others emotional states. A 2014 meta-analysis of 215 study samples by researchers Ashley E. Thompson and Daniel Voyer in the journal Cognition and Emotion found that there was "a small overall advantage in favour of females on emotion recognition tasks". Two 2015 reviews published in the journal Emotion review also found that adult women are more emotionally expressive,
but that the size of this gender difference varies with the social and
emotional context. Researchers distinguish three factors that predict
the size of gender differences in emotional expressiveness:
gender-specific norms, social role and situational constraints, and
emotional intensity.
A 2014 meta-analysis, in Cognition and Emotion, found overall female advantage in non-verbal emotional recognition.
A 2014 analysis from the journal Neuroscience & Biobehavioral Reviews also found that there are sex differences in empathy from birth,
growing larger with age and which remains consistent and stable across
lifespan. Females, on average, were found to have higher empathy than
males at all ages, and children with higher empathy regardless of gender
continue to possess high empathy throughout development in life.
Further analysis of brain tools such as event related potentials found
that females who viewed human suffering had higher ERP waveforms than males, an indication of greater empathetic response. Another investigation with similar brain tools such as N400
amplitudes found higher N400 in females in response to social
situations which then positively correlated with self-reported empathy.
Structural fMRI studies have also found females to have larger grey matter volumes in posterior inferior frontal and anterior inferior parietal cortex areas which have been correlated with mirror neurons indicated by the fMRI
literature. Mirror neurons are crucial for many if not most aspects of
empathy. Females were also found to have a stronger link between
emotional and cognitive empathy. The researchers use The Primary Caretaker Hypothesis
to explain the stability of these sex differences in development.
According to the hypothesis, prehistoric males did not have the same
selective pressure as women and this led to sex differences in emotion
recognition and empathy.
Research on the heritability of IQ inquires into the degree of variation in IQ within a population that is due to genetic variation
between individuals in that population. There has been significant
controversy in the academic community about the heritability of IQ since
research on the issue began in the late nineteenth century. Intelligence in the normal range is a polygenic trait, meaning that it is influenced by more than one gene, and in the case of intelligence at least 500 genes.
Further, explaining the similarity in IQ of closely related persons
requires careful study because environmental factors may be correlated
with genetic factors. Outside the normal range, certain single gene genetic disorders, such as phenylketonuria, can negatively affect intelligence.
Early twin studies of adult individuals have found a heritability of IQ between 57% and 73%, with some recent studies showing heritability for IQ as high as 80%.
IQ goes from being weakly correlated with genetics for children, to
being strongly correlated with genetics for late teens and adults. The
heritability of IQ increases with the child's age and reaches a plateau
at 14–16
years old, continuing at that level well into adulthood. However, poor
prenatal environment, malnutrition and disease are known to have
lifelong deleterious effects. Estimates in the academic research of the heritability of IQ have varied from below 0.5
to a high of 0.8 (where 1.0 indicates that monozygotic twins have no
variance in IQ and 0 indicates that their IQs are completely
uncorrelated).
Eric Turkheimer and colleagues (2003) found that for children of low
socioeconomic status heritability of IQ falls almost to zero.
These results have been challenged by other researchers. IQ
heritability increases during early childhood, but it is unclear whether
it stabilizes thereafter. A 1996 statement by the American Psychological Association gave about 0.45 for children and about .75 during and after adolescence. A 2004 meta-analysis of reports in Current Directions in Psychological Science gave an overall estimate of around 0.85 for 18-year-olds and older. The general figure for heritability of IQ is about 0.5 across multiple studies in varying populations.
Although IQ differences between individuals have been shown to
have a large hereditary component, it does not follow that disparities
in IQ between groups have a genetic basis. The scientific consensus is that genetics does not explain average differences in IQ test performance between racial groups.
Heritability is a statistic used in the fields of breeding and genetics that estimates the degree of variation in a phenotypic trait in a population that is due to genetic variation between individuals in that population.
The concept of heritability can be expressed in the form of the
following question: "What is the proportion of the variation in a given
trait within a population that is not explained by the environment or random chance?"
Estimates of heritability take values ranging from 0 to 1; a
heritability estimate of 1 indicates that all variation in the trait in
question is genetic in origin and a heritability estimate of 0 indicates
that none of the variation is genetic. The determination of many traits can be considered primarily genetic
under similar environmental backgrounds. For example, a 2006 study
found that adult height has a heritability estimated at 0.80 when
looking only at the height variation within families where the
environment should be very similar. Other traits have lower heritability estimates, which indicate a relatively larger environmental influence. For example, a twin study on the heritability of depression in men estimated it as 0.29, while it was 0.42 for women in the same study.
Caveats
There are a number of points to consider when interpreting heritability:
Heritability measures the proportion of variation in a trait that can be attributed to genes, and not the proportion of a trait caused by genes.
Thus, if the environment relevant to a given trait changes in a way
that affects all members of the population equally, the mean value of
the trait will change without any change in its heritability (because
the variation or differences among individuals in the population will
stay the same). This has evidently happened for height: the heritability
of stature is high, but average heights continue to increase.
Thus, even in developed nations, a high heritability of a trait does
not necessarily mean that average group differences are due to genes.
Some have gone further, and used height as an example in order to argue
that "even highly heritable traits can be strongly manipulated by the
environment, so heritability has little if anything to do with
controllability."
A common error is to assume that a heritability figure is
necessarily unchangeable. The value of heritability can change if the
impact of environment (or of genes) in the population is substantially
altered.
If the environmental variation encountered by different individuals
increases, then the heritability figure would decrease. On the other
hand, if everyone had the same environment, then heritability would be
100%. The population in developing nations often has more diverse
environments than in developed nations. This would mean that
heritability figures would be lower in developing nations. Another
example is phenylketonuria which previously caused intellectual disabilities
in everyone who had this genetic disorder and thus had a heritability
of 100%. Today, this can be prevented by following a modified diet,
resulting in a lowered heritability.
A high heritability of a trait does not mean that environmental
effects such as learning are not involved. Vocabulary size, for example,
is very substantially heritable (and highly correlated with general
intelligence) although every word in an individual's vocabulary is
learned. In a society in which plenty of words are available in
everyone's environment, especially for individuals who are motivated to
seek them out, the number of words that individuals actually learn
depends to a considerable extent on their genetic predispositions and
thus heritability is high.
Since heritability increases during childhood and adolescence, and
even increases greatly between 16 and 20 years of age and adulthood, one
should be cautious drawing conclusions regarding the role of genetics
and environment from studies where the participants are not followed
until they are adults. Furthermore, there may be differences regarding
the effects on the g-factor and on non-g factors, with g possibly being harder to affect and environmental interventions disproportionately affecting non-g factors.
Contrary to popular belief, two parents of higher IQ will not
necessarily produce offspring of equal or higher intelligence. Polygenic
traits often appear less heritable at the extremes. A heritable trait
is definitionally more likely to appear in the offspring of two parents
high in that trait than in the offspring of two randomly selected
parents. However, the more extreme the expression of the trait in the
parents, the less likely the child is to display the same extreme as the
parents. In fact, parents whose IQ is at either extreme are more likely
to produce offspring with IQ closer to the mean (or average) than they
are to produce offspring with high IQ. At the same time, the more
extreme the expression of the trait in the parents, the more likely the
child is to express the trait at all. For example, the child of two
extremely tall parents is likely to be taller than the average person
(displaying the trait), but unlikely to be taller than the two parents
(displaying the trait at the same extreme). See also regression toward the mean.
Estimates
Various studies have estimated the heritability of IQ to be between 0.7 and 0.8 in adults and 0.45 in childhood in the United States.
It has been found that estimates of heritability increase as
individuals age. Heritability estimates in infancy are as low as 0.2,
around 0.4 in middle childhood, and as high as 0.8 in adulthood.
The brain undergoes morphological changes in development which suggests
that age-related physical changes could contribute to this effect.
A 1994 article in Behavior Genetics based on a study of
Swedish monozygotic and dizygotic twins found the heritability of the
sample to be as high as 0.80 in general cognitive ability; however, it
also varies by trait, with 0.60 for verbal tests, 0.50 for spatial and
speed-of-processing tests, and 0.40 for memory tests. In contrast,
studies of other populations estimate an average heritability of 0.50
for general cognitive ability.
In 2006, David Kirp, writing in The New York Times Magazine,
summarized a century's worth of research as follows, "about
three-quarters of I.Q. differences between individuals are attributable
to heredity" while also highlighting that "much of what is labeled
'hereditary' becomes meaningful only in the context of experience."
There are some family effects on the IQ of children, accounting for
up to a quarter of the variance. However, adoption studies show that by
adulthood adoptive siblings aren't more similar in IQ than strangers,
while adult full siblings show an IQ correlation of 0.24. However, some
studies of twins reared apart (e.g. Bouchard, 1990) find a significant
shared environmental influence, of at least 10% going into late
adulthood. Judith Rich Harris suggests that this might be due to biasing assumptions in the methodology of the classical twin and adoption studies.
There are aspects of environments that family members have in
common (for example, characteristics of the home). This shared family
environment accounts for 0.25-0.35 of the variation in IQ in childhood.
By late adolescence it is quite low (zero in some studies). There is a
similar effect for several other psychological traits. These studies
have not looked into the effects of extreme environments such as in
abusive families.
The American Psychological Association's report "Intelligence: Knowns and Unknowns" (1996) asserts the necessity of a certain minimum level of responsible care for normal child development.
Environments that are severely deprived, neglectful, or abusive
negatively affect various developmental aspects, including intellectual
growth. Beyond this minimum threshold, the influence of family
experience on child development is contentious. Variables such as home
resources and parents' use of language are correlated with children's IQ
scores; however, these correlations may be influenced by genetic as
well as environmental factors. The extent to which variance in IQ
results from differences between families, compared to the varying
experiences of different children within the same family, is a subject
of debate. Recent twin and adoption studies indicate that the effect of
the shared family environment is significant in early childhood but
diminishes substantially by late adolescence. These findings suggest
that differences in family lifestyles, while potentially important for
many aspects of children's lives, have little long-term impact on the
skills measured by intelligence tests.
Non-shared family environment and environment outside the family
Although
parents treat their children differently, such differential treatment
explains only a small amount of non-shared environmental influence. One
suggestion is that children react differently to the same environment
due to different genes. More likely influences may be the impact of
peers and other experiences outside the family.
For example, siblings grown up in the same household may have different
friends and teachers and even contract different illnesses. This factor
may be one of the reasons why IQ score correlations between siblings
decreases as they get older.
Malnutrition and diseases
Certain single-gene metabolic disorders can severely affect intelligence. Phenylketonuria is an example, with publications documenting the capacity of treated phenylketonuria to produce a reduction of 10 IQ points on average. Meta-analyses have found that environmental factors, such as iodine deficiency,
can result in large reductions in average IQ; iodine deficiency has
been shown to produce a reduction of 12.5 IQ points on average.
Heritability and socioeconomic status
The APA report "Intelligence: Knowns and Unknowns" (1996) also stated that:
"We should note, however, that low-income
and non-white families are poorly represented in existing adoption
studies as well as in most twin samples. Thus it is not yet clear
whether these studies apply to the population as a whole. It remains
possible that, across the full range of income and ethnicity,
between-family differences have more lasting consequences for
psychometric intelligence."
A study (1999) by Capron and Duyme of French children adopted between the ages of four and six examined the influence of socioeconomic status
(SES). The children's IQs initially averaged 77, putting them near
retardation. Most were abused or neglected as infants, then shunted from
one foster home or institution to the next. Nine years later after
adoption, when they were on average 14 years old, they retook the IQ
tests, and all of them did better. The amount they improved was directly
related to the adopting family's socioeconomic status. "Children
adopted by farmers and laborers had average IQ scores of 85.5; those
placed with middle-class
families had average scores of 92. The average IQ scores of youngsters
placed in well-to-do homes climbed more than 20 points, to 98."
Stoolmiller
(1999) argued that the range of environments in previous adoption
studies was restricted. Adopting families tend to be more similar on,
for example, socio-economic status than the general population, which
suggests a possible underestimation of the role of the shared family
environment in previous studies. Corrections for range restriction to
adoption studies indicated that socio-economic status could account for
as much as 50% of the variance in IQ.
On the other hand, the effect of this was examined by Matt McGue
and colleagues (2007), who wrote that "restriction in range in parent
disinhibitory psychopathology and family socio-economic status had no
effect on adoptive-sibling correlations [in] IQ"
Turkheimer
and colleagues (2003) argued that the proportions of IQ variance
attributable to genes and environment vary with socioeconomic status.
They found that in a study on seven-year-old twins, in impoverished
families, 60% of the variance in early childhood IQ was accounted for by
the shared family environment, and the contribution of genes is close
to zero; in affluent families, the result is almost exactly the reverse.
In contrast to Turkheimer (2003), a study by Nagoshi and Johnson
(2005) concluded that the heritability of IQ did not vary as a function
of parental socioeconomic status in the 949 families of Caucasian and
400 families of Japanese ancestry who took part in the Hawaii Family
Study of Cognition.
Asbury and colleagues (2005) studied the effect of environmental
risk factors on verbal and non-verbal ability in a nationally
representative sample of 4-year-old British twins. There was not any
statistically significant interaction for non-verbal ability, but the
heritability of verbal ability was found to be higher in low-SES and high-risk environments.
Harden, Turkheimer, and Loehlin
(2007) investigated adolescents, most 17 years old, and found that,
among higher income families, genetic influences accounted for
approximately 55% of the variance in cognitive aptitude and shared
environmental influences about 35%. Among lower income families, the
proportions were in the reverse direction, 39% genetic and 45% shared
environment."
In the course of a substantial review, Rushton and Jensen
(2010) criticized the study of Capron and Duyme, arguing their choice
of IQ test and selection of child and adolescent subjects were a poor
choice because this gives a relatively less hereditable measure. The argument here rests on a strong form of Spearman's hypothesis, that the hereditability of different kinds of IQ test can vary according to how closely they correlate to the general intelligence factor (g); both the empirical data and statistical methodology bearing on this question are matters of active controversy.
A 2011 study by Tucker-Drob
and colleagues reported that at age 2, genes accounted for
approximately 50% of the variation in mental ability for children being
raised in high socioeconomic status families, but genes accounted for
negligible variation in mental ability for children being raised in low
socioeconomic status families. This gene–environment interaction was not
apparent at age 10 months, suggesting that the effect emerges over the
course of early development.
A 2012 study based on a representative sample of twins from the United Kingdom,
with longitudinal data on IQ from age two to age fourteen, did not find
evidence for lower heritability in low-SES families. However, the study
indicated that the effects of shared family environment on IQ were
generally greater in low-SES families than in high-SES families,
resulting in greater variance in IQ in low-SES families. The authors
noted that previous research had produced inconsistent results on
whether or not SES moderates the heritability of IQ. They suggested
three explanations for the inconsistency. First, some studies may have
lacked statistical power to detect interactions. Second, the age range
investigated has varied between studies. Third, the effect of SES may
vary in different demographics and different countries.
Maternal (fetal) environment
A meta-analysis
by Devlin and colleagues (1997) of 212 previous studies evaluated an
alternative model for environmental influence and found that it fits the
data better than the 'family-environments' model commonly used. The
shared maternal (fetal)
environment effects, often assumed to be negligible, account for 20% of
covariance between twins and 5% between siblings, and the effects of
genes are correspondingly reduced, with two measures of heritability
being less than 50%. They argue that the shared maternal environment may
explain the striking correlation between the IQs of twins, especially
those of adult twins that were reared apart. IQ heritability increases during early childhood, but whether it stabilizes thereafter remains unclear.
These results have two implications: a new model may be required
regarding the influence of genes and environment on cognitive function;
and interventions aimed at improving the prenatal environment could lead
to a significant boost in the population's IQ.
Bouchard and McGue reviewed the literature in 2003, arguing that
Devlin's conclusions about the magnitude of heritability is not
substantially different from previous reports and that their conclusions
regarding prenatal effects stands in contradiction to many previous
reports. They write that:
Chipuer
et al. and Loehlin conclude that the postnatal rather than the prenatal
environment is most important. The Devlin et al. (1997a) conclusion
that the prenatal environment contributes to twin IQ similarity is
especially remarkable given the existence of an extensive empirical
literature on prenatal effects. Price (1950), in a comprehensive review
published over 50 years ago, argued that almost all MZ twin prenatal
effects produced differences rather than similarities. As of 1950 the
literature on the topic was so large that the entire bibliography was
not published. It was finally published in 1978 with an additional 260
references. At that time Price reiterated his earlier conclusion (Price,
1978). Research subsequent to the 1978 review largely reinforces
Price's hypothesis (Bryan, 1993; Macdonald et al., 1993; Hall and
Lopez-Rangel, 1996; see also Martin et al., 1997, box 2; Machin, 1996).
Dickens and Flynn model
Dickens and Flynn (2001) argued that the "heritability" figure includes both a direct effect of the genotype
on IQ and also indirect effects where the genotype changes the
environment, in turn affecting IQ. That is, those with a higher IQ tend
to seek out stimulating environments that further increase IQ. The
direct effect can initially have been very small but feedback
loops can create large differences in IQ. In their model an
environmental stimulus can have a very large effect on IQ, even in
adults, but this effect also decays over time unless the stimulus
continues. This model could be adapted to include possible factors, like nutrition in early childhood, that may cause permanent effects.
The Flynn effect
is the increase in average intelligence test scores by about 0.3%
annually, resulting in the average person today scoring 15 points higher
in IQ compared to the generation 50 years ago.
This effect can be explained by a generally more stimulating
environment for all people.
Some scientists have suggested that such enhancements are due to better
nutrition, better parenting and schooling, as well as exclusion of the
least intelligent people from reproduction. However, Flynn and a group
of other scientists share the viewpoint that modern life implies solving
many abstract problems which leads to a rise in their IQ scores.
Influence of genes on IQ stability
Recent research has illuminated genetic factors underlying IQ stability and change. Genome-wide association studies have demonstrated that the genes involved in intelligence remain fairly stable over time.
Specifically, in terms of IQ stability, "genetic factors mediated
phenotypic stability throughout this entire period [age 0 to 16],
whereas most age-to-age instability appeared to be due to non-shared
environmental influences".These findings have been replicated extensively and observed in the United Kingdom, the United States, and the Netherlands. Additionally, researchers have shown that naturalistic changes in IQ occur in individuals at variable times.
Influence of parents genes that are not inherited
Kong
reports that, "Nurture has a genetic component, i.e. alleles in the
parents affect the parents' phenotypes and through that influence the
outcomes of the child." These results were obtained through a
meta-analysis of educational attainment and polygenic
scores of non-transmitted alleles. Although the study deals with
educational attainment and not IQ, these two are strongly linked.
Spatial ability component of IQ
Spatial
ability has been shown to be unifactorial (a single score accounts well
for all spatial abilities), and is 69% heritable in a sample of 1,367
pairs of twins from the ages 19 through 21. Further only 8% of spatial ability can be accounted for by shared environmental factors like school and family.
Of the genetically determined portion of spatial ability, 24% is shared
with verbal ability (general intelligence) and 43% was specific to
spatial ability alone.
Molecular genetic investigations
A 2009 review article identified over 50 genetic polymorphisms
that have been reported to be associated with cognitive ability in
various studies, but noted that the discovery of small effect sizes and
lack of replication have characterized this research so far.
Another study attempted to replicate 12 reported associations between
specific genetic variants and general cognitive ability in three large
datasets, but found that only one of the genotypes was significantly
associated with general intelligence in one of the samples, a result
expected by chance alone. The authors concluded that most reported
genetic associations with general intelligence are probably false positives brought about by inadequate sample sizes.
Arguing that common genetic variants explain much of the variation in
general intelligence, they suggested that the effects of individual
variants are so small that very large samples are required to reliably
detect them. Genetic diversity within individuals is heavily correlated with IQ.
A novel molecular genetic method for estimating heritability
calculates the overall genetic similarity (as indexed by the cumulative
effects of all genotyped single nucleotide polymorphisms)
between all pairs of individuals in a sample of unrelated individuals
and then correlates this genetic similarity with phenotypic similarity
across all the pairs. A study using this method estimated that the lower
bounds for the narrow-sense heritability of crystallized and fluid
intelligence are 40% and 51%, respectively. A replication study in an
independent sample confirmed these results, reporting a heritability
estimate of 47%.
These findings are compatible with the view that a large number of
genes, each with only a small effect, contribute to differences in
intelligence.
Correlations between IQ and degree of genetic relatedness
The relative influence of genetics and environment for a trait can be calculated by measuring how strongly traits covary
in people of a given genetic (unrelated, siblings, fraternal twins, or
identical twins) and environmental (reared in the same family or not)
relationship. One method is to consider identical twins reared apart, with any similarities that exist between such twin pairs attributed to genotype. In terms of correlation statistics, this means that theoretically the correlation of tests scores between monozygotic twins would be 1.00 if genetics alone accounted for variation in IQ scores; likewise, siblings and dizygotic twins share on average half alleles
and the correlation of their scores would be 0.50 if IQ were affected
by genes alone (or greater if there is a positive correlation between
the IQs of spouses in the parental generation). Practically, however,
the upper bound of these correlations are given by the reliability of the test, which is 0.90 to 0.95 for typical IQ tests.
If there is biological inheritance
of IQ, then the relatives of a person with a high IQ should exhibit a
comparably high IQ with a much higher probability than the general
population. In 1982, Bouchard and McGue reviewed such correlations
reported in 111 original studies in the United States. The mean
correlation of IQ scores between monozygotic twins was 0.86, between
siblings 0.47, between half-siblings 0.31, and between cousins 0.15.
The 2006 edition of Assessing adolescent and adult intelligence by Alan S. Kaufman
and Elizabeth O. Lichtenberger reports correlations of 0.86 for
identical twins raised together compared to 0.76 for those raised apart
and 0.47 for siblings.
These numbers are not necessarily static. When comparing pre-1963 to
late 1970s data, researchers DeFries and Plomin found that the IQ
correlation between parent and child living together fell significantly,
from 0.50 to 0.35. The opposite occurred for fraternal twins.
Every one of these studies presented next contains estimates of
only two of the three factors which are relevant. The three factors are
G, E, and GxE. Since there is no possibility of studying equal
environments in a manner comparable to using identical twins for equal
genetics, the GxE factor can not be isolated. Thus the estimates are
actually of G+GxE and E. Although this may seem like nonsense, it is
justified by the unstated assumption that GxE=0. It is also the case
that the values shown below are r correlations and not r(squared),
proportions of variance. Numbers less than one are smaller when squared.
The next to last number in the list below refers to less than 5% shared
variance between a parent and child living apart.
In the US, individuals identifying themselves as Asian generally tend
to score higher on IQ tests than Caucasians, who tend to score higher
than Hispanics, who tend to score higher than African Americans.
Yet, although IQ differences between individuals have been shown to
have a large hereditary component, it does not follow that between-group
differences in average IQ have a genetic basis. In fact, greater variation in IQ scores exists within each ethnic group than between them. The scientific consensus is that genetics does not explain average differences in IQ test performance between racial groups. Growing evidence indicates that environmental factors, not genetic ones, explain the racial IQ gap.
Arguments in support of a genetic explanation of racial
differences in average IQ are sometimes fallacious. For instance, some
hereditarians have cited as evidence the failure of known environmental
factors to account for such differences, or the high heritability of
intelligence within races. Jensen and Rushton, in their formulation of Spearman's Hypothesis, argued that cognitive tasks that have the highest g-load
are the tasks in which the gap between black and white test takers is
greatest, and that this supports their view that racial IQ gaps are in
large part genetic. However, in separate reviews, Mackintosh, Nisbett et al. and Flynn have all concluded that the slight correlation between g-loading and the test score gap offers no clue to the cause of the gap. Further reviews of both adoption studies and racial admixture studies have also found no evidence for a genetic component behind group-level IQ differences.
Hereditarian arguments for racial differences in IQ have been
criticized from a theoretical point of view as well. For example, the
geneticist and neuroscientist Kevin Mitchell has argued that "systematic
genetic differences in intelligence between large, ancient populations"
are "inherently and deeply implausible" because the "constant churn of
genetic variation works against any long-term rise or fall in
intelligence."
As he argues, "To end up with systematic genetic differences in
intelligence between large, ancient populations, the selective forces
driving those differences would need to have been enormous. What's more,
those forces would have to have acted across entire continents, with
wildly different environments, and have been persistent over tens of
thousands of years of tremendous cultural change."
In favor of an environmental explanation, on the other hand,
numerous studies and reviews have shown promising results. Among these,
some focus on the gradual closing of the black–white IQ gap over the
last decades of the 20th century, as black test-takers increased their
average scores relative to white test-takers. For instance, Vincent
reported in 1991 that the black–white IQ gap was decreasing among
children, but that it was remaining constant among adults.
Similarly, a 2006 study by Dickens and Flynn estimated that the
difference between mean scores of black people and white people closed
by about 5 or 6 IQ points between 1972 and 2002, a reduction of about
one-third. In the same period, the educational achievement disparity also diminished. Reviews by Flynn and Dickens, Mackintosh, and Nisbett et al. all accept the gradual closing of the gap as a fact. Other recent studies have focused on disparities in nutrition and
prenatal care, as well as other health-related environmental
disparities, and have found that these disparities may account for
significant IQ gaps between population groups.
Still other studies have focused on educational disparities, and have
found that intensive early childhood education and test preparation can
diminish or eliminate the black–white IQ test gap.
In light of these and similar findings, a consensus has formed that
genetics does not explain differences in average IQ test performance
between racial groups.
A factory worker with a prosthetic arm using a lathe to produce artificial limbs c. 1944
In medicine, a prosthesis (pl.: prostheses; from Ancient Greek: πρόσθεσις, romanized: prósthesis, lit. 'addition, application, attachment'), or a prosthetic implant, is an artificial device that replaces a missing body part, which may be lost through physical trauma, disease, or a condition present at birth (congenital disorder). Prostheses may restore the normal functions of the missing body part, or may perform a cosmetic function.
A person who has undergone an amputation is sometimes referred to as an amputee, however, this term may be offensive. Rehabilitation for someone with an amputation is primarily coordinated by a physiatrist
as part of an inter-disciplinary team consisting of physiatrists,
prosthetists, nurses, physical therapists, and occupational therapists. Prostheses can be created by hand or with computer-aided design (CAD), a software interface that helps creators design and analyze the creation with computer-generated 2-D and 3-D graphics as well as analysis and optimization tools.
Types
A
person's prosthetic device should be designed and assembled to meet
their individual appearance and functional needs. Depending on personal
circumstances, co-morbidities, budget or health insurance coverage, and
access to medical care, decisions may need to balance aesthetics and
function. In addition, for some individuals, a myoelectric device, a
body-powered device, or an activity-specific device may be appropriate
options. The person's future goals and vocational aspirations and
potential capabilities may help them choose between one or more devices.
Limb prostheses include both upper- and lower-extremity prostheses.
Upper-extremity prostheses are used at varying levels of
amputation: forequarter, shoulder disarticulation, transhumeral
prosthesis, elbow disarticulation, transradial prosthesis, wrist
disarticulation, full hand, partial hand, finger, partial finger. A
transradial prosthesis is an artificial limb that replaces an arm
missing below the elbow.
An example of two upper-extremity prosthetics, one body-powered (right arm), and another myoelectric (left arm)
Upper limb prostheses can be categorized in three main categories:
Passive devices, Body Powered devices, and Externally Powered
(myoelectric) devices. Passive devices can either be passive hands,
mainly used for cosmetic purposes, or passive tools, mainly used for
specific activities (e.g. leisure or vocational). An extensive overview
and classification of passive devices can be found in a literature
review by Maat et.al.
A passive device can be static, meaning the device has no movable
parts, or it can be adjustable, meaning its configuration can be
adjusted (e.g. adjustable hand opening). Despite the absence of active
grasping, passive devices are very useful in bimanual tasks that require
fixation or support of an object, or for gesticulation in social
interaction. According to scientific data a third of the upper limb
amputees worldwide use a passive prosthetic hand.
Body Powered or cable-operated limbs work by attaching a harness and
cable around the opposite shoulder of the damaged arm. A recent
body-powered approach has explored the utilization of the user's
breathing to power and control the prosthetic hand to help eliminate
actuation cable and harness.
The third category of available prosthetic devices comprises
myoelectric arms. This particular class of devices distinguishes itself
from the previous ones due to the inclusion of a battery system. This
battery serves the dual purpose of providing energy for both actuation
and sensing components. While actuation predominantly relies on motor or
pneumatic systems, a variety of solutions have been explored for capturing muscle activity, including techniques such as Electromyography, Sonomyography, Myokinetic, and others. These methods function by detecting the minute electrical currents generated by contracted muscles during upper arm
movement, typically employing electrodes or other suitable tools.
Subsequently, these acquired signals are converted into gripping
patterns or postures that the artificial hand will then execute.
In the prosthetics industry, a trans-radial prosthetic arm is often referred to as a "BE" or below elbow prosthesis.
Lower-extremity prostheses provide replacements at varying levels of amputation. These include hip disarticulation,
transfemoral prosthesis, knee disarticulation, transtibial prosthesis,
Syme's amputation, foot, partial foot, and toe. The two main
subcategories of lower extremity prosthetic devices are trans-tibial
(any amputation transecting the tibia bone or a congenital anomaly
resulting in a tibial deficiency) and trans-femoral (any amputation
transecting the femur bone or a congenital anomaly resulting in a
femoral deficiency).
A transfemoral prosthesis is an artificial limb that replaces a
leg missing above the knee. Transfemoral amputees can have a very
difficult time regaining normal movement. In general, a transfemoral
amputee must use approximately 80% more energy to walk than a person
with two whole legs.
This is due to the complexities in movement associated with the knee.
In newer and more improved designs, hydraulics, carbon fiber, mechanical
linkages, motors, computer microprocessors, and innovative combinations
of these technologies are employed to give more control to the user. In
the prosthetics industry, a trans-femoral prosthetic leg is often
referred to as an "AK" or above the knee prosthesis.
A transtibial prosthesis is an artificial limb that replaces a
leg missing below the knee. A transtibial amputee is usually able to
regain normal movement more readily than someone with a transfemoral
amputation, due in large part to retaining the knee, which allows for
easier movement. Lower extremity prosthetics describe artificially
replaced limbs located at the hip level or lower. In the prosthetics
industry, a trans-tibial prosthetic leg is often referred to as a "BK"
or below the knee prosthesis.
Prostheses are manufactured and fit by clinical prosthetists.
Prosthetists are healthcare professionals responsible for making,
fitting, and adjusting prostheses and for lower limb prostheses will
assess both gait and prosthetic alignment. Once a prosthesis has been
fit and adjusted by a prosthetist, a rehabilitation physiotherapist
(called physical therapist in America) will help teach a new prosthetic
user to walk with a leg prosthesis. To do so, the physical therapist may
provide verbal instructions and may also help guide the person using
touch or tactile cues. This may be done in a clinic or home. There is
some research suggesting that such training in the home may be more
successful if the treatment includes the use of a treadmill.
Using a treadmill, along with the physical therapy treatment, helps the
person to experience many of the challenges of walking with a
prosthesis.
In the United Kingdom, 75% of lower limb amputations are performed due to inadequate circulation (dysvascularity). This condition is often associated with many other medical conditions (co-morbidities) including diabetes and heart disease that may make it a challenge to recover and use a prosthetic limb to regain mobility and independence.
For people who have inadequate circulation and have lost a lower limb,
there is insufficient evidence due to a lack of research, to inform them
regarding their choice of prosthetic rehabilitation approaches.
Types of prosthesis used for replacing joints in the human body
Lower extremity prostheses are often categorized by the level of amputation or after the name of a surgeon:
Transfemoral (Above-knee)
Transtibial (Below-knee)
Ankle disarticulation (more commonly known as Syme's amputation)
Partial foot amputations (Pirogoff, Talo-Navicular and
Calcaneo-cuboid (Chopart), Tarso-metatarsal (Lisfranc),
Trans-metatarsal, Metatarsal-phalangeal, Ray amputations, toe
amputations).
Van Nes rotationplasty
Prosthetic raw materials
Prosthetic are made lightweight for better convenience for the amputee. Some of these materials include:
Plastics:
Polyethylene
Polypropylene
Acrylics
Polyurethane
Wood (early prosthetics)
Rubber (early prosthetics)
Lightweight metals:
Aluminum
Composites:
Carbon fiber reinforced polymers
Wheeled prostheses have also been used extensively in the
rehabilitation of injured domestic animals, including dogs, cats, pigs,
rabbits, and turtles.
Prosthetics originate from the ancient Near East circa 3000 BCE, with the earliest evidence of prosthetics appearing in ancient Egypt and Iran. The earliest recorded mention of eye prosthetics is from the Egyptian story of the Eye of Horus dated circa 3000 BC, which involves the left eye of Horus being plucked out and then restored by Thoth.
Circa 3000-2800 BC, the earliest archaeological evidence of prosthetics
is found in ancient Iran, where an eye prosthetic is found buried with a
woman in Shahr-i Shōkhta. It was likely made of bitumen paste that was covered with a thin layer of gold. The Egyptians were also early pioneers of foot prosthetics, as shown by the wooden toe found on a body from the New Kingdom circa 1000 BC. Another early textual mention is found in South Asia circa 1200 BC, involving the warrior queen Vishpala in the Rigveda. Roman bronze crowns have also been found, but their use could have been more aesthetic than medical.
An early mention of a prosthetic comes from the Greek historian Herodotus, who tells the story of Hegesistratus, a Greek diviner who cut off his own foot to escape his Spartan captors and replaced it with a wooden one.[26]
Wood and metal prosthetics
The Capua leg (replica)A wooden prosthetic leg from Shengjindian cemetery, circa 300 BCE, Turpan Museum. This is "the oldest functional leg prosthesis known to date".Iron prosthetic hand believed to have been owned by Götz von Berlichingen (1480–1562)"Illustration of mechanical hand", c. 1564Artificial iron hand believed to date from 1560 to 1600
Pliny the Elder also recorded the tale of a Roman general, Marcus Sergius, whose right hand was cut off while campaigning and had an iron hand made to hold his shield so that he could return to battle. A famous and quite refined historical prosthetic arm was that of Götz von Berlichingen,
made at the beginning of the 16th century. The first confirmed use of a
prosthetic device, however, is from 950 to 710 BC. In 2000, research
pathologists discovered a mummy from this period buried in the Egyptian
necropolis near ancient Thebes that possessed an artificial big toe.
This toe, consisting of wood and leather, exhibited evidence of use.
When reproduced by bio-mechanical engineers in 2011, researchers
discovered that this ancient prosthetic enabled its wearer to walk both
barefoot and in Egyptian style sandals. Previously, the earliest
discovered prosthetic was an artificial leg from Capua.
Around the same time, François de la Noue is also reported to have had an iron hand, as is, in the 17th century, René-Robert Cavalier de la Salle. Henri de Tonti
had a prosthetic hook for a hand. During the Middle Ages, prosthetics
remained quite basic in form. Debilitated knights would be fitted with
prosthetics so they could hold up a shield, grasp a lance or a sword, or
stabilize a mounted warrior. Only the wealthy could afford anything that would assist in daily life.
One notable prosthesis was that belonging to an Italian man, who
scientists estimate replaced his amputated right hand with a knife. Scientists investigating the skeleton, which was found in a Longobard cemetery in Povegliano Veronese, estimated that the man had lived sometime between the 6th and 8th centuries AD.
Materials found near the man's body suggest that the knife prosthesis
was attached with a leather strap, which he repeatedly tightened with
his teeth.
During the Renaissance, prosthetics developed with the use of
iron, steel, copper, and wood. Functional prosthetics began to make an
appearance in the 1500s.
Technology progress before the 20th century
An
Italian surgeon recorded the existence of an amputee who had an arm
that allowed him to remove his hat, open his purse, and sign his name. Improvement in amputation surgery and prosthetic design came at the hands of Ambroise Paré. Among his inventions was an above-knee device that was a kneeling peg leg
and foot prosthesis with a fixed position, adjustable harness, and knee
lock control. The functionality of his advancements showed how future
prosthetics could develop.
Other major improvements before the modern era:
Pieter Verduyn – First non-locking below-knee (BK) prosthesis.
James Potts –
Prosthesis made of a wooden shank and socket, a steel knee joint and an
articulated foot that was controlled by catgut tendons from the knee to
the ankle. Came to be known as "Anglesey Leg" or "Selpho Leg".
Sir James Syme – A new method of ankle amputation that did not involve amputating at the thigh.
Benjamin Palmer – Improved upon the Selpho leg. Added an anterior spring and concealed tendons to simulate natural-looking movement.
Dubois Parmlee – Created prosthetic with a suction socket, polycentric knee, and multi-articulated foot.
Henry Heather Bigg, and his son Henry Robert Heather Bigg, won the
Queen's command to provide "surgical appliances" to wounded soldiers
after Crimea War. They developed arms that allowed a double arm amputee
to crochet, and a hand that felt natural to others based on ivory, felt
and leather.
At the end of World War II, the NAS (National Academy of Sciences)
began to advocate better research and development of prosthetics.
Through government funding, a research and development program was
developed within the Army, Navy, Air Force, and the Veterans
Administration.
Lower extremity modern history
An artificial limbs factory in 1941
After the Second World War, a team at the University of California, Berkeley including James Foort
and C.W. Radcliff helped to develop the quadrilateral socket by
developing a jig fitting system for amputations above the knee. Socket
technology for lower extremity limbs saw a further revolution during the
1980s when John Sabolich C.P.O., invented the Contoured Adducted
Trochanteric-Controlled Alignment Method (CATCAM) socket, later to
evolve into the Sabolich Socket. He followed the direction of Ivan Long
and Ossur Christensen as they developed alternatives to the
quadrilateral socket, which in turn followed the open ended plug socket,
created from wood.
The advancement was due to the difference in the socket to patient
contact model. Prior to this, sockets were made in the shape of a square
shape with no specialized containment for muscular tissue. New designs
thus help to lock in the bony anatomy, locking it into place and
distributing the weight evenly over the existing limb as well as the
musculature of the patient. Ischial containment is well known and used
today by many prosthetist to help in patient care. Variations of the
ischial containment socket thus exists and each socket is tailored to
the specific needs of the patient. Others who contributed to socket
development and changes over the years include Tim Staats, Chris Hoyt,
and Frank Gottschalk. Gottschalk disputed the efficacy of the CAT-CAM
socket- insisting the surgical procedure done by the amputation surgeon
was most important to prepare the amputee for good use of a prosthesis
of any type socket design.
The first microprocessor-controlled prosthetic knees became
available in the early 1990s. The Intelligent Prosthesis was the first
commercially available microprocessor-controlled prosthetic knee. It was
released by Chas. A. Blatchford & Sons, Ltd., of Great Britain, in
1993 and made walking with the prosthesis feel and look more natural.
An improved version was released in 1995 by the name Intelligent
Prosthesis Plus. Blatchford released another prosthesis, the Adaptive
Prosthesis, in 1998. The Adaptive Prosthesis utilized hydraulic
controls, pneumatic controls, and a microprocessor to provide the
amputee with a gait that was more responsive to changes in walking
speed. Cost analysis reveals that a sophisticated above-knee prosthesis
will be about $1 million in 45 years, given only annual cost of living
adjustments.
In 2019, a project under AT2030 was launched in which bespoke
sockets are made using a thermoplastic, rather than through a plaster
cast. This is faster to do and significantly less expensive. The sockets
were called Amparo Confidence sockets.
Upper extremity modern history
DARPA Revolutionizing Prosthetics - The LUKE Arm
In 2005, DARPA started the Revolutionizing Prosthetics program.
According to DARPA, the goal of the $100 million program was to
"develop an advanced electromechanical prosthetic upper limb with
near-natural control that would dramatically enhance independence and
quality of life for amputees."In 2014, the LUKE Arm developed by Dean Kamen and his team at DEKA Research and Development Corp. became the first prosthetic arm approved by FDA that "translates signals from a person's muscles to perform complex tasks," according to FDA. Johns Hopkins University and the U.S. Department of Veteran Affairs also participated in the program.
Design trends moving forward
There
are many steps in the evolution of prosthetic design trends that are
moving forward with time. Many design trends point to lighter, more
durable, and flexible materials like carbon fiber, silicone, and
advanced polymers. These not only make the prosthetic limb lighter and
more durable but also allow it to mimic the look and feel of natural
skin, providing users with a more comfortable and natural experience.
This new technology helps prosthetic users blend in with people with
normal ligaments to reduce the stigmatism for people who wear
prosthetics. Another trend points towards using bionics
and myoelectric components in prosthetic design. These limbs utilize
sensors to detect electrical signals from the user's residual muscles.
The signals are then converted into motions, allowing users to control
their prosthetic limbs using their own muscle contractions. This has
greatly improved the range and fluidity of movements available to
amputees, making tasks like grasping objects or walking naturally much
more feasible.
Integration with AI is also on the forefront to the prosthetic design.
AI-enabled prosthetic limbs can learn and adapt to the user's habits and
preferences over time, ensuring optimal functionality. By analyzing the
user's gait, grip, and other movements, these smart limbs can make
real-time adjustments, providing smoother and more natural motions.
Patient procedure
A prosthesis is a functional replacement for an amputated or congenitally malformed or missing limb. Prosthetists are responsible for the prescription, design, and management of a prosthetic device.
In most cases, the prosthetist begins by taking a plaster cast of
the patient's affected limb. Lightweight, high-strength thermoplastics
are custom-formed to this model of the patient. Cutting-edge materials
such as carbon fiber, titanium and Kevlar provide strength and
durability while making the new prosthesis lighter. More sophisticated
prostheses are equipped with advanced electronics, providing additional
stability and control.
Over the years, there have been advancements in artificial limbs. New plastics and other materials, such as carbon fiber,
have allowed artificial limbs to be stronger and lighter, limiting the
amount of extra energy necessary to operate the limb. This is especially
important for trans-femoral amputees. Additional materials have allowed
artificial limbs to look much more realistic, which is important to
trans-radial and transhumeral amputees because they are more likely to
have the artificial limb exposed.
Manufacturing a prosthetic finger
In addition to new materials, the use of electronics has become very
common in artificial limbs. Myoelectric limbs, which control the limbs
by converting muscle movements to electrical signals, have become much
more common than cable operated limbs. Myoelectric signals are picked up
by electrodes, the signal gets integrated and once it exceeds a certain
threshold, the prosthetic limb control signal is triggered which is why
inherently, all myoelectric controls lag. Conversely, cable control is
immediate and physical, and through that offers a certain degree of
direct force feedback that myoelectric control does not. Computers are
also used extensively in the manufacturing of limbs. Computer Aided Design and Computer Aided Manufacturing are often used to assist in the design and manufacture of artificial limbs.
Most modern artificial limbs are attached to the residual limb (stump) of the amputee by belts and cuffs or by suction.
The residual limb either directly fits into a socket on the prosthetic,
or—more commonly today—a liner is used that then is fixed to the socket
either by vacuum (suction sockets) or a pin lock. Liners are soft and
by that, they can create a far better suction fit than hard sockets.
Silicone liners can be obtained in standard sizes, mostly with a
circular (round) cross section, but for any other residual limb shape,
custom liners can be made. The socket is custom made to fit the residual
limb and to distribute the forces of the artificial limb across the
area of the residual limb (rather than just one small spot), which helps
reduce wear on the residual limb.
Production of prosthetic socket
The
production of a prosthetic socket begins with capturing the geometry of
the residual limb; this process is called shape capture. The goal of
this process is to create an accurate representation of the residual
limb, which is critical to achieve good socket fit.
The custom socket is created by taking a plaster cast of the residual
limb or, more commonly today, of the liner worn over their residual
limb, and then making a mold from the plaster cast. The commonly used
compound is called Plaster of Paris.
In recent years, various digital shape capture systems have been
developed which can be input directly to a computer allowing for a more
sophisticated design. In general, the shape capturing process begins
with the digital acquisition of three-dimensional (3D) geometric data
from the amputee's residual limb. Data are acquired with either a probe,
laser scanner, structured light scanner, or a photographic-based 3D
scanning system.
After shape capture, the second phase of the socket production is
called rectification, which is the process of modifying the model of
the residual limb by adding volume to bony prominence and potential
pressure points and remove volume from load bearing area. This can be
done manually by adding or removing plaster to the positive model, or
virtually by manipulating the computerized model in the software.
Lastly, the fabrication of the prosthetic socket begins once the model
has been rectified and finalized. The prosthetists would wrap the
positive model with a semi-molten plastic sheet or carbon fiber coated
with epoxy resin to construct the prosthetic socket.
For the computerized model, it can be 3D printed using a various of
material with different flexibility and mechanical strength.
Optimal socket fit between the residual limb and socket is
critical to the function and usage of the entire prosthesis. If the fit
between the residual limb and socket attachment is too loose, this will
reduce the area of contact between the residual limb and socket or
liner, and increase pockets between residual limb skin and socket or
liner. Pressure then is higher, which can be painful. Air pockets can
allow sweat to accumulate that can soften the skin. Ultimately, this is a
frequent cause for itchy skin rashes. Over time, this can lead to
breakdown of the skin.
On the other hand, a very tight fit may excessively increase the
interface pressures that may also lead to skin breakdown after prolonged
use.
Artificial limbs are typically manufactured using the following steps:
Measurement of the residual limb
Measurement of the body to determine the size required for the artificial limb
Fitting of a silicone liner
Creation of a model of the liner worn over the residual limb
Formation of thermoplastic sheet around the model – This is then used to test the fit of the prosthetic
Formation of permanent socket
Formation of plastic parts of the artificial limb – Different methods are used, including vacuum forming and injection molding
Creation of metal parts of the artificial limb using die casting
Assembly of entire limb
Body-powered arms
Current technology allows body-powered arms to weigh around one-half to one-third of what a myoelectric arm does.
Sockets
Current
body-powered arms contain sockets that are built from hard epoxy or
carbon fiber. These sockets or "interfaces" can be made more comfortable
by lining them with a softer, compressible foam material that provides
padding for the bone prominences. A self-suspending or supra-condylar
socket design is useful for those with short to mid-range below elbow
absence. Longer limbs may require the use of a locking roll-on type
inner liner or more complex harnessing to help augment suspension.
Wrists
Wrist
units are either screw-on connectors featuring the UNF 1/2-20 thread
(USA) or quick-release connector, of which there are different models.
Voluntary opening and voluntary closing
Two
types of body-powered systems exist, voluntary opening "pull to open"
and voluntary closing "pull to close". Virtually all "split hook"
prostheses operate with a voluntary opening type system.
More modern "prehensors" called GRIPS utilize voluntary closing
systems. The differences are significant. Users of voluntary opening
systems rely on elastic bands or springs for gripping force, while users
of voluntary closing systems rely on their own body power and energy to
create gripping force.
Voluntary closing users can generate prehension forces equivalent
to the normal hand, up to or exceeding one hundred pounds. Voluntary
closing GRIPS require constant tension to grip, like a human hand, and
in that property, they do come closer to matching human hand
performance. Voluntary opening split hook users are limited to forces
their rubber or springs can generate which usually is below 20 pounds.
Feedback
An
additional difference exists in the biofeedback created that allows the
user to "feel" what is being held. Voluntary opening systems once
engaged provide the holding force so that they operate like a passive
vice at the end of the arm. No gripping feedback is provided once the
hook has closed around the object being held. Voluntary closing systems
provide directly proportional control and biofeedback so that the user can feel how much force that they are applying.
In 1997, the Colombian Prof. Álvaro Ríos Poveda, a researcher in bionics in Latin America, developed an upper limb and hand prosthesis with sensory feedback. This technology allows amputee patients to handle prosthetic hand systems in a more natural way.
A recent study showed that by stimulating the median and ulnar
nerves, according to the information provided by the artificial sensors
from a hand prosthesis, physiologically appropriate (near-natural)
sensory information could be provided to an amputee. This feedback
enabled the participant to effectively modulate the grasping force of
the prosthesis with no visual or auditory feedback.
In February 2013, researchers from École Polytechnique Fédérale de Lausanne in Switzerland and the Scuola Superiore Sant'Anna
in Italy, implanted electrodes into an amputee's arm, which gave the
patient sensory feedback and allowed for real time control of the
prosthetic.
With wires linked to nerves in his upper arm, the Danish patient was
able to handle objects and instantly receive a sense of touch through
the special artificial hand that was created by Silvestro Micera and
researchers both in Switzerland and Italy.
In July 2019, this technology was expanded on even further by researchers from the University of Utah,
led by Jacob George. The group of researchers implanted electrodes into
the patient's arm to map out several sensory precepts. They would then
stimulate each electrode to figure out how each sensory precept was
triggered, then proceed to map the sensory information onto the
prosthetic. This would allow the researchers to get a good approximation
of the same kind of information that the patient would receive from
their natural hand. Unfortunately, the arm is too expensive for the
average user to acquire, however, Jacob mentioned that insurance
companies could cover the costs of the prosthetic.
Terminal devices
Terminal devices contain a range of hooks, prehensors, hands or other devices.
Hooks
Voluntary opening split hook systems are simple, convenient, light, robust, versatile and relatively affordable.
A hook does not match a normal human hand for appearance or
overall versatility, but its material tolerances can exceed and surpass
the normal human hand for mechanical stress (one can even use a hook to
slice open boxes or as a hammer whereas the same is not possible with a
normal hand), for thermal stability (one can use a hook to grip items
from boiling water, to turn meat on a grill, to hold a match until it
has burned down completely) and for chemical hazards (as a metal hook
withstands acids or lye, and does not react to solvents like a
prosthetic glove or human skin).
Hands
Actor Owen Wilson gripping the myoelectric prosthetic arm of a United States Marine
Prosthetic hands are available in both voluntary opening and
voluntary closing versions and because of their more complex mechanics
and cosmetic glove covering require a relatively large activation force,
which, depending on the type of harness used, may be uncomfortable.
A recent study by the Delft University of Technology, The Netherlands,
showed that the development of mechanical prosthetic hands has been
neglected during the past decades. The study showed that the pinch force
level of most current mechanical hands is too low for practical use.
The best tested hand was a prosthetic hand developed around 1945. In
2017 however, a research has been started with bionic hands by Laura Hruby of the Medical University of Vienna. A few open-hardware 3-D printable bionic hands have also become available. Some companies are also producing robotic hands with integrated forearm, for fitting unto a patient's upper arm
and in 2020, at the Italian Institute of Technology (IIT), another
robotic hand with integrated forearm (Soft Hand Pro) was developed.
Commercial providers and materials
Hosmer and Otto Bock
are major commercial hook providers. Mechanical hands are sold by
Hosmer and Otto Bock as well; the Becker Hand is still manufactured by
the Becker family. Prosthetic hands may be fitted with standard stock or
custom-made cosmetic looking silicone gloves. But regular work gloves
may be worn as well. Other terminal devices include the V2P Prehensor, a
versatile robust gripper that allows customers to modify aspects of it,
Texas Assist Devices (with a whole assortment of tools) and TRS that
offers a range of terminal devices for sports. Cable harnesses can be
built using aircraft steel cables, ball hinges, and self-lubricating
cable sheaths. Some prosthetics have been designed specifically for use
in salt water.
Lower-extremity prosthetics describes artificially replaced limbs
located at the hip level or lower. Concerning all ages Ephraim et al.
(2003) found a worldwide estimate of all-cause lower-extremity
amputations of 2.0–5.9 per 10,000 inhabitants. For birth prevalence
rates of congenital limb deficiency they found an estimate between 3.5
and 7.1 cases per 10,000 births.
The two main subcategories of lower extremity prosthetic devices
are trans-tibial (any amputation transecting the tibia bone or a
congenital anomaly resulting in a tibial deficiency), and trans-femoral
(any amputation transecting the femur bone or a congenital anomaly
resulting in a femoral deficiency). In the prosthetic industry, a
trans-tibial prosthetic leg is often referred to as a "BK" or below the
knee prosthesis while the trans-femoral prosthetic leg is often referred
to as an "AK" or above the knee prosthesis.
Other, less prevalent lower extremity cases include the following:
Hip disarticulations – This usually refers to when an amputee or
congenitally challenged patient has either an amputation or anomaly at
or in close proximity to the hip joint. See hip replacement
Knee disarticulations – This usually refers to an amputation through the knee disarticulating the femur from the tibia. See knee replacement
Symes – This is an ankle disarticulation while preserving the heel pad.
Socket
The
socket serves as an interface between the residuum and the prosthesis,
ideally allowing comfortable weight-bearing, movement control and proprioception. Socket problems, such as discomfort and skin breakdown, are rated among the most important issues faced by lower-limb amputees.
Shank and connectors
This
part creates distance and support between the knee-joint and the foot
(in case of an upper-leg prosthesis) or between the socket and the foot.
The type of connectors that are used between the shank and the
knee/foot determines whether the prosthesis is modular or not. Modular
means that the angle and the displacement of the foot in respect to the
socket can be changed after fitting. In developing countries prosthesis
mostly are non-modular, in order to reduce cost. When considering
children modularity of angle and height is important because of their
average growth of 1.9 cm annually.
Foot
Providing contact to the ground, the foot provides shock absorption and stability during stance.
Additionally it influences gait biomechanics by its shape and
stiffness. This is because the trajectory of the center of pressure
(COP) and the angle of the ground reaction forces is determined by the
shape and stiffness of the foot and needs to match the subject's build
in order to produce a normal gait pattern.
Andrysek (2010) found 16 different types of feet, with greatly varying
results concerning durability and biomechanics. The main problem found
in current feet is durability, endurance ranging from 16 to 32 months
These results are for adults and will probably be worse for children
due to higher activity levels and scale effects. Evidence comparing
different types of feet and ankle prosthetic devices is not strong
enough to determine if one mechanism of ankle/foot is superior to
another.[87]
When deciding on a device, the cost of the device, a person's
functional need, and the availability of a particular device should be
considered.
In case of a trans-femoral (above knee) amputation, there also is a
need for a complex connector providing articulation, allowing flexion
during swing-phase but not during stance. As its purpose is to replace
the knee, the prosthetic knee joint is the most critical component of
the prosthesis for trans-femoral amputees. The function of the good
prosthetic knee joint is to mimic the function of the normal knee, such
as providing structural support and stability during stance phase but
able to flex in a controllable manner during swing phase. Hence it
allows users to have a smooth and energy efficient gait and minimize the
impact of amputation. The prosthetic knee is connected to the prosthetic foot by the shank, which is usually made of an aluminum or graphite tube.
One of the most important aspect of a prosthetic knee joint would
be its stance-phase control mechanism. The function of stance-phase
control is to prevent the leg from buckling when the limb is loaded
during weight acceptance. This ensures the stability of the knee in
order to support the single limb support task of stance phase and
provides a smooth transition to the swing phase. Stance phase control
can be achieved in several ways including the mechanical locks, relative alignment of prosthetic components, weight activated friction control, and polycentric mechanisms.
Microprocessor control
To
mimic the knee's functionality during gait, microprocessor-controlled
knee joints have been developed that control the flexion of the knee.
Some examples are Otto Bock's C-leg, introduced in 1997, Ossur's
Rheo Knee, released in 2005, the Power Knee by Ossur, introduced in
2006, the Plié Knee from Freedom Innovations and DAW Industries' Self
Learning Knee (SLK).
The idea was originally developed by Kelly James, a Canadian engineer, at the University of Alberta.
A microprocessor is used to interpret and analyze signals from
knee-angle sensors and moment sensors. The microprocessor receives
signals from its sensors to determine the type of motion being employed
by the amputee. Most microprocessor controlled knee-joints are powered
by a battery housed inside the prosthesis.
The sensory signals computed by the microprocessor are used to control the resistance generated by hydraulic cylinders in the knee-joint. Small valves control the amount of hydraulic fluid
that can pass into and out of the cylinder, thus regulating the
extension and compression of a piston connected to the upper section of
the knee.
The main advantage of a microprocessor-controlled prosthesis is a
closer approximation to an amputee's natural gait. Some allow amputees
to walk near walking speed or run. Variations in speed are also possible
and are taken into account by sensors and communicated to the
microprocessor, which adjusts to these changes accordingly. It also
enables the amputees to walk downstairs with a step-over-step approach,
rather than the one step at a time approach used with mechanical knees.
There is some research suggesting that people with
microprocessor-controlled prostheses report greater satisfaction and
improvement in functionality, residual limb health, and safety. People may be able to perform everyday activities at greater speeds, even while multitasking, and reduce their risk of falls.
However, some have some significant drawbacks that impair its
use. They can be susceptible to water damage and thus great care must be
taken to ensure that the prosthesis remains dry.
Myoelectric
A myoelectric prosthesis
uses the electrical tension generated every time a muscle contracts, as
information. This tension can be captured from voluntarily contracted
muscles by electrodes applied on the skin to control the movements of
the prosthesis, such as elbow flexion/extension, wrist
supination/pronation (rotation) or opening/closing of the fingers. A
prosthesis of this type utilizes the residual neuromuscular system of
the human body to control the functions of an electric powered
prosthetic hand, wrist, elbow or foot.
This is different from an electric switch prosthesis, which requires
straps and/or cables actuated by body movements to actuate or operate
switches that control the movements of the prosthesis. There is no clear
evidence concluding that myoelectric upper extremity prostheses
function better than body-powered prostheses.
Advantages to using a myoelectric upper extremity prosthesis include
the potential for improvement in cosmetic appeal (this type of
prosthesis may have a more natural look), may be better for light
everyday activities, and may be beneficial for people experiencing phantom limb pain.
When compared to a body-powered prosthesis, a myoelectric prosthesis
may not be as durable, may have a longer training time, may require more
adjustments, may need more maintenance, and does not provide feedback
to the user.
Prof. Alvaro Ríos Poveda
has been working for several years on a non-invasive and affordable
solution to this feedback problem. He considers that: "Prosthetic limbs
that can be controlled with thought hold great promise for the amputee,
but without sensorial feedback from the signals returning to the brain,
it can be difficult to achieve the level of control necessary to perform
precise movements. When connecting the sense of touch from a mechanical
hand directly to the brain, prosthetics can restore the function of the
amputated limb in an almost natural-feeling way." He presented the
first Myoelectric prosthetic hand with sensory feedback at the XVIII World Congress on Medical Physics and Biomedical Engineering, 1997, held in Nice, France.
The USSR was the first to develop a myoelectric arm in 1958, while the first myoelectric arm became commercial in 1964 by the Central Prosthetic Research Institute of the USSR, and distributed by the Hangar Limb Factory of the UK.
The Myoelectric prosthesis are expensive requires regular maintenance,
sensitive to sweat and moisture affecting sensor performance.
Robots can be used to generate objective measures of patient's
impairment and therapy outcome, assist in diagnosis, customize therapies
based on patient's motor abilities, and assure compliance with
treatment regimens and maintain patient's records. It is shown in many
studies that there is a significant improvement in upper limb motor
function after stroke using robotics for upper limb rehabilitation.
In order for a robotic prosthetic limb to work, it must have several components to integrate it into the body's function: Biosensors detect signals from the user's nervous or muscular systems. It then relays this information to a microcontroller
located inside the device, and processes feedback from the limb and
actuator, e.g., position or force, and sends it to the controller.
Examples include surface electrodes that detect electrical activity on
the skin, needle electrodes implanted in muscle, or solid-state
electrode arrays with nerves growing through them. One type of these
biosensors are employed in myoelectric prostheses.
A device known as the controller is connected to the user's nerve
and muscular systems and the device itself. It sends intention commands
from the user to the actuators of the device and interprets feedback
from the mechanical and biosensors to the user. The controller is also
responsible for the monitoring and control of the movements of the
device.
An actuator
mimics the actions of a muscle in producing force and movement.
Examples include a motor that aids or replaces original muscle tissue.
Targeted muscle reinnervation (TMR) is a technique in which motor nerves, which previously controlled muscles on an amputated limb, are surgically rerouted such that they reinnervate a small region of a large, intact muscle, such as the pectoralis major.
As a result, when a patient thinks about moving the thumb of their
missing hand, a small area of muscle on their chest will contract
instead. By placing sensors over the reinnervated muscle, these
contractions can be made to control the movement of an appropriate part
of the robotic prosthesis.
A variant of this technique is called targeted sensory reinnervation (TSR). This procedure is similar to TMR, except that sensory nerves are surgically rerouted to skin
on the chest, rather than motor nerves rerouted to muscle. Recently,
robotic limbs have improved in their ability to take signals from the human brain and translate those signals into motion in the artificial limb. DARPA,
the Pentagon's research division, is working to make even more
advancements in this area. Their desire is to create an artificial limb
that ties directly into the nervous system.
Robotic arms
Advancements
in the processors used in myoelectric arms have allowed developers to
make gains in fine-tuned control of the prosthetic. The Boston Digital Arm
is a recent artificial limb that has taken advantage of these more
advanced processors. The arm allows movement in five axes and allows the
arm to be programmed for a more customized feel. Recently the I-LIMB Hand, invented in Edinburgh, Scotland, by David Gow
has become the first commercially available hand prosthesis with five
individually powered digits. The hand also possesses a manually
rotatable thumb which is operated passively by the user and allows the
hand to grip in precision, power, and key grip modes.
Another neural prosthetic is Johns Hopkins University Applied Physics Laboratory Proto 1. Besides the Proto 1, the university also finished the Proto 2 in 2010.
Early in 2013, Max Ortiz Catalan and Rickard Brånemark of the Chalmers
University of Technology, and Sahlgrenska University Hospital in Sweden,
succeeded in making the first robotic arm which is mind-controlled and
can be permanently attached to the body (using osseointegration).
An approach that is very useful is called arm rotation which is
common for unilateral amputees which is an amputation that affects only
one side of the body; and also essential for bilateral amputees, a
person who is missing or has had amputated either both arms or legs, to
carry out activities of daily living. This involves inserting a small
permanent magnet into the distal end of the residual bone of subjects
with upper limb amputations. When a subject rotates the residual arm,
the magnet will rotate with the residual bone, causing a change in
magnetic field distribution.
EEG (electroencephalogram) signals, detected using small flat metal
discs attached to the scalp, essentially decoding human brain activity
used for physical movement, is used to control the robotic limbs. This
allows the user to control the part directly.
Robotic transtibial prostheses
The research of robotic legs has made some advancement over time, allowing exact movement and control.
Researchers at the Rehabilitation Institute of Chicago
announced in September 2013 that they have developed a robotic leg that
translates neural impulses from the user's thigh muscles into movement,
which is the first prosthetic leg to do so. It is currently in testing.
Hugh Herr, head of the biomechatronics group at MIT's Media Lab developed a robotic transtibial leg (PowerFoot BiOM).
The Icelandic company Össur has also created a robotic
transtibial leg with motorized ankle that moves through algorithms and
sensors that automatically adjust the angle of the foot during different
points in its wearer's stride. Also there are brain-controlled bionic
legs that allow an individual to move his limbs with a wireless
transmitter.
Prosthesis design
The
main goal of a robotic prosthesis is to provide active actuation during
gait to improve the biomechanics of gait, including, among other
things, stability, symmetry, or energy expenditure for amputees.
There are several powered prosthetic legs currently on the market,
including fully powered legs, in which actuators directly drive the
joints, and semi-active legs, which use small amounts of energy and a
small actuator to change the mechanical properties of the leg but do not
inject net positive energy into gait. Specific examples include The
emPOWER from BionX, the Proprio Foot from Ossur, and the Elan Foot from
Endolite. Various research groups have also experimented with robotic legs over the last decade.
Central issues being researched include designing the behavior of the
device during stance and swing phases, recognizing the current
ambulation task, and various mechanical design problems such as
robustness, weight, battery-life/efficiency, and noise-level. However,
scientists from Stanford University and Seoul National University has developed artificial nerves system that will help prosthetic limbs feel. This synthetic nerve system enables prosthetic limbs sense braille, feel the sense of touch and respond to the environment.
Use of recycled materials
Prosthetics are being made from recycled plastic bottles and lids around the world.
Most prostheses are attached to the exterior of the body in a
non-permanent way. The stump and socket method can cause significant
pain for the person, which is why direct bone attachment has been
explored extensively.
Osseointegration is a method of attaching the artificial limb to the body by a prosthetic implant.
This method is also sometimes referred to as exoprosthesis (attaching an artificial limb to the bone), or endo-exoprosthesis.
Endoprosthesis are prosthetic joint implants which remain wholly inside the body such as knee and hip replacement implants.
The method works by inserting a titanium bolt into the bone at the end of the stump. After several months the bone attaches itself
to the titanium bolt and an abutment is attached to the titanium bolt.
The abutment extends out of the stump and the (removable) artificial
limb is then attached to the abutment. Some of the benefits of this
method include the following:
Better muscle control of the prosthetic.
The ability to wear the prosthetic for an extended period of time; with the stump and socket method this is not possible.
The ability for transfemoral amputees to drive a car.
The main disadvantage of this method is that amputees with the direct
bone attachment cannot have large impacts on the limb, such as those
experienced during jogging, because of the potential for the bone to
break.
Cosmesis
Cosmetic prosthesis has long been used to disguise injuries and disfigurements. With advances in modern technology, cosmesis, the creation of lifelike limbs made from silicone or PVC, has been made possible.
Such prosthetics, including artificial hands, can now be designed to
simulate the appearance of real hands, complete with freckles, veins,
hair, fingerprints and even tattoos.
Custom-made cosmeses are generally more expensive (costing thousands of
U.S. dollars, depending on the level of detail), while standard cosmeses
come premade in a variety of sizes, although they are often not as
realistic as their custom-made counterparts. Another option is the
custom-made silicone cover, which can be made to match a person's skin
tone but not details such as freckles or wrinkles. Cosmeses are attached
to the body in any number of ways, using an adhesive, suction,
form-fitting, stretchable skin, or a skin sleeve.
Unlike neuromotor prostheses, neurocognitive prostheses would sense
or modulate neural function in order to physically reconstitute or
augment cognitive processes such as executive function, attention,
language, and memory. No neurocognitive prostheses are currently
available but the development of implantable neurocognitive
brain-computer interfaces has been proposed to help treat conditions
such as stroke, traumatic brain injury, cerebral palsy, autism, and Alzheimer's disease.
The recent field of Assistive Technology for Cognition concerns the
development of technologies to augment human cognition. Scheduling
devices such as Neuropage remind users with memory impairments when to
perform certain activities, such as visiting the doctor. Micro-prompting
devices such as PEAT, AbleLink and Guide have been used to aid users
with memory and executive function problems perform activities of daily living.
Sgt. Jerrod Fields works out at the U.S. Olympic Training Center in Chula Vista, California.
In addition to the standard artificial limb for everyday use, many amputees or congenital patients have special limbs and devices to aid in the participation of sports and recreational activities.
Within science fiction, and, more recently, within the scientific community,
there has been consideration given to using advanced prostheses to
replace healthy body parts with artificial mechanisms and systems to
improve function. The morality and desirability of such technologies are
being debated by transhumanists, other ethicists, and others in general. Body parts such as legs, arms, hands, feet, and others can be replaced.
The first experiment with a healthy individual appears to have been that by the British scientist Kevin Warwick. In 2002, an implant was interfaced directly into Warwick's nervous system. The electrode array, which contained around a hundred electrodes, was placed in the median nerve. The signals produced were detailed enough that a robot arm was able to mimic the actions of Warwick's own arm and provide a form of touch feedback again via the implant.
The DEKA company of Dean Kamen developed the "Luke arm", an advanced nerve-controlled prosthetic. Clinical trials began in 2008, with FDA approval in 2014 and commercial manufacturing by the Universal Instruments Corporation expected in 2017. The price offered at retail by Mobius Bionics is expected to be around $100,000.
Further research in April 2019, there have been improvements
towards prosthetic function and comfort of 3D-printed personalized
wearable systems. Instead of manual integration after printing,
integrating electronic sensors at the intersection between a prosthetic
and the wearer's tissue can gather information such as pressure across
wearer's tissue, that can help improve further iteration of these types
of prosthetic.
Oscar Pistorius
In early 2008, Oscar Pistorius, the "Blade Runner" of South Africa, was briefly ruled ineligible to compete in the 2008 Summer Olympics
because his transtibial prosthesis limbs were said to give him an
unfair advantage over runners who had ankles. One researcher found that
his limbs used twenty-five percent less energy than those of a
non-disabled runner moving at the same speed. This ruling was overturned
on appeal, with the appellate court stating that the overall set of
advantages and disadvantages of Pistorius' limbs had not been
considered.
Pistorius did not qualify for the South African team for the Olympics, but went on to sweep the 2008 Summer Paralympics, and has been ruled eligible to qualify for any future Olympics.
He qualified for the 2011 World Championship in South Korea and reached
the semi-final where he ended last timewise, he was 14th in the first
round, his personal best at 400m would have given him 5th place in the
finals. At the 2012 Summer Olympics in London, Pistorius became the first amputee runner to compete at an Olympic Games. He ran in the 400 metres race semi-finals, and the 4 × 400 metres relay race finals. He also competed in 5 events in the 2012 Summer Paralympics in London.
Design considerations
There
are multiple factors to consider when designing a transtibial
prosthesis. Manufacturers must make choices about their priorities
regarding these factors.
Performance
Nonetheless,
there are certain elements of socket and foot mechanics that are
invaluable for the athlete, and these are the focus of today's high-tech
prosthetics companies:
Fit – athletic/active amputees, or those with bony residua, may
require a carefully detailed socket fit; less-active patients may be
comfortable with a 'total contact' fit and gel liner
Energy storage and return – storage of energy acquired through
ground contact and utilization of that stored energy for propulsion
Energy absorption – minimizing the effect of high impact on the musculoskeletal system
Ground compliance – stability independent of terrain type and angle
Rotation – ease of changing direction
Weight – maximizing comfort, balance and speed
Suspension – how the socket will join and fit to the limb
Other
The buyer is also concerned with numerous other factors:
Cosmetics
Cost
Ease of use
Size availability
Design for Prosthetics
A
key feature of prosthetics and prosthetic design is the idea of
“designing for disabilities.” This might sound like a good idea in which
people with disabilities can participate in equitable design but this
is unfortunately not true. The idea of designing for disabilities is
first problematic because of the underlying meaning of disabilities. It
tells amputees that there is a right and wrong way to move and walk and
that if amputees are adapted to the surrounding environment by their own
means, then that is the wrong way. Along with that underlying meaning
of disabilities, many people designing for disabilities are not actually
disabled. “Design for disability" from these experiences, takes
disability as the object - with the feeling from non-disabled designers
that they have properly learned about their job from their own
simulation of the experience. The simulation is misleading and does a
disservice to disabled people - so the design that flows from this is
highly problematic. Engaging in disability design should be… with,
ideally, team members who have the relevant disability and are part of
communities that matter to the research.
This leads to people, who do not know what the day-to-day personal
experiences are, designing materials that do not meet the needs or
hinder the needs of people with actual disabilities.
Cost and source freedom
High-cost
In
the USA a typical prosthetic limb costs anywhere between $15,000 and
$90,000, depending on the type of limb desired by the patient. With
medical insurance, a patient will typically pay 10%–50% of the total
cost of a prosthetic limb, while the insurance company will cover the
rest of the cost. The percent that the patient pays varies on the type
of insurance plan, as well as the limb requested by the patient.
In the United Kingdom, much of Europe, Australia and New Zealand the
entire cost of prosthetic limbs is met by state funding or statutory
insurance. For example, in Australia prostheses are fully funded by
state schemes in the case of amputation due to disease, and by workers
compensation or traffic injury insurance in the case of most traumatic
amputations. The National Disability Insurance Scheme, which is being rolled out nationally between 2017 and 2020 also pays for prostheses.
Transradial (below the elbow amputation) and transtibial prostheses (below the knee amputation) typically cost between US $6,000
and $8,000, while transfemoral (above the knee amputation) and
transhumeral prosthetics (above the elbow amputation) cost approximately
twice as much with a range of $10,000 to $15,000 and can sometimes
reach costs of $35,000. The cost of an artificial limb often recurs,
while a limb typically needs to be replaced every 3–4 years due to wear and tear
of everyday use. In addition, if the socket has fit issues, the socket
must be replaced within several months from the onset of pain. If height
is an issue, components such as pylons can be changed.
Not only does the patient need to pay for their multiple
prosthetic limbs, but they also need to pay for physical and
occupational therapy that come along with adapting to living with an
artificial limb. Unlike the reoccurring cost of the prosthetic limbs,
the patient will typically only pay the $2000 to $5000 for therapy
during the first year or two of living as an amputee. Once the patient
is strong and comfortable with their new limb, they will not be required
to go to therapy anymore. Throughout one's life, it is projected that a
typical amputee will go through $1.4 million worth of treatment,
including surgeries, prosthetics, as well as therapies.
Low-cost above-knee prostheses often provide only basic structural
support with limited function. This function is often achieved with
crude, non-articulating, unstable, or manually locking knee joints. A
limited number of organizations, such as the International Committee of
the Red Cross (ICRC), create devices for developing countries. Their
device which is manufactured by CR Equipments is a single-axis, manually
operated locking polymer prosthetic knee joint.
Table. List of knee joint technologies based on the literature review.
A plan for a low-cost artificial leg, designed by Sébastien Dubois,
was featured at the 2007 International Design Exhibition and award show
in Copenhagen, Denmark, where it won the Index: Award. It would be able to create an energy-return prosthetic leg for US $8.00, composed primarily of fiberglass.
Prior to the 1980s, foot prostheses merely restored basic walking
capabilities. These early devices can be characterized by a simple
artificial attachment connecting one's residual limb to the ground.
The introduction of the Seattle Foot (Seattle Limb Systems) in
1981 revolutionized the field, bringing the concept of an Energy Storing
Prosthetic Foot (ESPF) to the fore. Other companies soon followed suit,
and before long, there were multiple models of energy storing
prostheses on the market. Each model utilized some variation of a
compressible heel. The heel is compressed during initial ground contact,
storing energy which is then returned during the latter phase of ground
contact to help propel the body forward.
Since then, the foot prosthetics industry has been dominated by
steady, small improvements in performance, comfort, and marketability.
With 3D printers, it is possible to manufacture a single product without having to have metal molds, so the costs can be drastically reduced.
There is currently an open-design Prosthetics forum known as the "Open Prosthetics Project".
The group employs collaborators and volunteers to advance Prosthetics
technology while attempting to lower the costs of these necessary
devices. Open Bionics
is a company that is developing open-source robotic prosthetic hands.
They utilize 3D printing to manufacture the devices and low-cost 3D
scanners to fit them onto the residual limb of a specific patient. Open
Bionics' use of 3D printing allows for more personalized designs, such
as the "Hero Arm" which incorporates the users favourite colours,
textures, and even aesthetics to look like superheroes or characters
from Star Wars with the aim of lowering the cost. A review study
on a wide range of printed prosthetic hands found that 3D printing
technology holds a promise for individualised prosthesis design, is
cheaper than commercial prostheses available on the market, and is more
expensive than mass production processes such as injection molding. The
same study also found that evidence on the functionality, durability and
user acceptance of 3D printed hand prostheses is still lacking.
Artificial limbs for a juvenile thalidomide survivor 1961–1965
In the USA an estimate was found of 32,500 children (<21 years)
had a major paediatric amputation, with 5,525 new cases each year, of
which 3,315 congenital.
Carr et al. (1998) investigated amputations caused by landmines
for Afghanistan, Bosnia and Herzegovina, Cambodia and Mozambique among
children (<14 years), showing estimates of respectively 4.7, 0.19,
1.11 and 0.67 per 1000 children.
Mohan (1986) indicated in India a total of 424,000 amputees (23,500
annually), of which 10.3% had an onset of disability below the age of
14, amounting to a total of about 43,700 limb deficient children in
India alone.
Few low-cost solutions have been created specially for children. Examples of low-cost prosthetic devices include:
Pole and crutch
This
hand-held pole with leather support band or platform for the limb is
one of the simplest and cheapest solutions found. It serves well as a
short-term solution, but is prone to rapid contracture formation if the
limb is not stretched daily through a series of range-of motion (RoM)
sets.
Bamboo, PVC or plaster limbs
This
also fairly simple solution comprises a plaster socket with a bamboo or
PVC pipe at the bottom, optionally attached to a prosthetic foot. This
solution prevents contractures because the knee is moved through its
full RoM. The David Werner Collection, an online database for the
assistance of disabled village children, displays manuals of production
of these solutions.
Adjustable bicycle limb
This
solution is built using a bicycle seat post up side down as foot,
generating flexibility and (length) adjustability. It is a very cheap
solution, using locally available materials.
Sathi Limb
It
is an endoskeletal modular lower limb from India, which uses
thermoplastic parts. Its main advantages are the small weight and
adaptability.
Monolimb
Monolimbs
are non-modular prostheses and thus require more experienced
prosthetist for correct fitting, because alignment can barely be changed
after production. However, their durability on average is better than
low-cost modular solutions.
Cultural and social theory perspectives
A number of theorists have explored the meaning and implications of prosthetic extension of the body. Elizabeth Grosz
writes, "Creatures use tools, ornaments, and appliances to augment
their bodily capacities. Are their bodies lacking something, which they
need to replace with artificial or substitute organs?...Or conversely,
should prostheses be understood, in terms of aesthetic reorganization
and proliferation, as the consequence of an inventiveness that functions
beyond and perhaps in defiance of pragmatic need?" Elaine Scarry
argues that every artifact recreates and extends the body. Chairs
supplement the skeleton, tools append the hands, clothing augments the
skin.
In Scarry's thinking, "furniture and houses are neither more nor less
interior to the human body than the food it absorbs, nor are they
fundamentally different from such sophisticated prosthetics as
artificial lungs, eyes and kidneys. The consumption of manufactured
things turns the body inside out, opening it up to and as the culture of objects." Mark Wigley,
a professor of architecture, continues this line of thinking about how
architecture supplements our natural capabilities, and argues that "a
blurring of identity is produced by all prostheses." Some of this work relies on Freud's earlier characterization of man's relation to objects as one of extension.
Negative social implications
Prosthetics
play a vital role in how a person perceives themselves and how other
people perceive them. The ability to conceal such use enabled
participants to ward off social stigmatization that in turn enabled
their social integration and the reduction of emotional problems
surrounding such disability.
People that lose a limb first have to deal with the emotional result of
losing that limb. Regardless of the reasons for amputation, whether due
to traumatic causes or as a consequence of illness, emotional shock
exists. It may have a smaller or larger amplitude depending on a variety
of factors such as patient age, medical culture, medical cause, etc. As
a result of amputation, the research participants' reports were loaded
with drama. The first emotional response to amputation was one of
despair, a severe sense of self-collapse, something almost unbearable.
Emotional factors are just a small part of looking at social
implications. Many people who lose a limb may have lots of anxiety
surrounding prosthetics and their limbs. After surgery, for an extended
period of time, the interviewed patients from the National Library of
Medicine noticed the appearance and increase of anxiety. A lot of
negative thoughts invaded their minds. Projections about the future were
grim, marked by sadness, helplessness, and even despair. Existential
uncertainty, lack of control, and further anticipated losses in one's
life due to amputation were the primary causes of anxiety and
consequently ruminations and insomnia.
From losing a leg and getting a prosthetics there were also many
factors that can happen including anger and regret. The amputation of a
limb is associated not only with physical loss and change in body image
but also with an abrupt severing in one's sense of continuity. For
participants with amputation as a result of physical trauma the event is
often experienced as a transgression and can lead to frustration and
anger.
Ethical concerns
There
are also many ethical concerns about how the prosthetics are made and
produced. A wide range of ethical issues arise in connection with
experiments and clinical usage of sensory prostheses: animal
experimentation; informed consent, for instance, in patients with a
locked-in syndrome that may be alleviated with a sensory prosthesis;
unrealistic expectations of research subjects testing new devices.
How prosthetics come to be and testing of the usability of the device
is a major concern in the medical world. Although many positives come
when a new prosthetic design is announced, how the device got to where
it is leads to some questioning the ethics of prosthetics.
Debates
There
are also many debates among the prosthetic community about whether they
should wear prosthetics at all. This is sparked by whether prosthetics
help in day-to-day living or make it harder. Many people have adapted to
their loss of limb making it work for them and do not need a prosthesis
in their life. Not all amputees will wear a prosthesis. In a 2011
national survey of Australian amputees, Limbs 4 Life found that 7
percent of amputees do not wear a prosthesis, and in another Australian
hospital study, this number was closer to 20 percent.
Many people report being uncomfortable in prostheses and not wanting to
wear them, even reporting that wearing a prosthetic is more cumbersome
than not having one at all. These debates are natural among the
prosthetic community and help us shed light on the issues that they are
facing.
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