13 July 2019 | New Scientist | 15Ruby Prosser Scully Chelsea WhyteSURGEONS have reanimated the
hands and arms of people who are
paralysed by connecting working
nerves to injured ones, giving
recipients the ability to feed
themselves again, use their
phones and apply make-up.
The operation is life-changing,
says surgeon Natasha van Zyl at
Austin Health in Australia. One
recipient is now travelling in
Europe and another can take
his grandchild to the movies.
Her team in Melbourne and a
few other small groups around the
world have been developing this
technique over several years and
have seen promising results, but
published research has focused
only on individual cases or small
retrospective studies that can’t say
for sure how safe and effective it is.
So van Zyl and her colleagues
recruited 16 people with spinal
injuries that led to arm and leg
paralysis, otherwise known as
quadriplegia or tetraplegia, for
a more thorough assessment.
If an injury is relatively high up
on the spinal cord, it can lead to
arm paralysis because many of the
nerves through which we control
our arms branch off below theinjury site. But someone with
tetraplegia can still have limited
nerve activity in their arms, even
if they lack hand function for
example, because some nerves to
the limbs may branch away from
the spinal cord above the injury.
Van Zyl and her team spliced
these working nerves to non-
functioning ones below the injuryParalysed hands work
again after nerve ops
Surgerysite that help control movements
in the hands and elbows.
Two years after surgery, and
after intensive physical therapy,
13 participants still involved in the
study regained some hand andarm control – for instance, being
able to open their hands, grasp
and pinch again (The Lancet,
doi.org/c7zh).
This study is sufficient to
establish the safety and efficacy of
the surgery, says Jeremy Simcock
at the University of Otago in
Christchurch, New Zealand.
The nerve transfer technique is
similar to tendon transfer, which
Simcock says surgeons have been
using for 30 years to help people
with tetraplegic injury gain some
use of their hands. But unlike
tendon transfers, which usually
involve rerouting a working
tendon to provide one muscular
function, multiple nerve transfers
can be done at once and each one
can reanimate multiple muscles.
Each person in the study was
given at least one nerve transfer,
and many had an additional
tendon transfer.
“It’s a stronger hand [following
just tendon transfer], but it’s a bit
more clawed in its position and
not as natural in its feeling [as with
a nerve transfer],” says van Zyl.
“It doesn’t open as well.”
Van Zyl and her team have
performed about 160 of these
nerve transfer operations so
far, but she says many people
around the world don’t have
access to the technology.
She hopes the new study
will help ensure that more people
who are eligible are able to have
the surgery. ❚160
Rough number of people who
have had nerve transfer surgeryMovement
can return
to paralysed
limbs by
splicing
nerves
together
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DESPITE a lot of searching, we
haven’t found a moon around
an exoplanet yet. According to
a new study, that could be
because an exomoon can be
ejected from orbit around its
home world and turned into
a miniature planet called a
“ploonet”. This fate may even
befall our own moon one day.
Mario Sucerquia at the
University of Antioquia in
Colombia and his colleagues
modelled the interplay between
exomoons and the gas giant
planets they could form around.
These worlds are between
0.5 and 1.8 times the mass of
Neptune, orbiting stars at the
distance Mercury lies from the
sun. Their size and proximity to
their stars makes any exomoons
they have more detectable.
However, these worlds turn
out to be prone to losing moons.
That is because such exoplanets
form further out from their star
and migrate inward. When near
their star, its gravity can disturb
any moons they have,
potentially flinging them into
their own orbits around the star.
“Closer-in giant planets are
more prone to lose their moons
because the tidal interaction
between the star and the planetis stronger,” says Sucerquia.
“This is, in fact, bad news for
exomoon hunters.”
Sucerquia and his team
found that about 44 per cent
of ejected exomoons would
collide with their planet in
this process, about 6 per cent
would be absorbed by the star,
and about 2 per cent would
be flung out of the planetary
system entirely. But the rest
would become ploonets.
Of those, 54 per cent would
end up in orbits further from
the star than their home planet.
Another 14 per cent would
end up on orbits closer to the
star, and almost a third would
take on eccentric orbits where
the ploonet’s path would
cross the planet’s orbit every
once in a while (arxiv.org/
abs/1906.11400).
“Earth’s tidal strength is
gradually pushing the moon
away from us at a rate of
about 3 centimetres a year,”
says Sucerquia. “Therefore,
the moon is indeed a potential
ploonet once it reaches an
unstable orbit.” ❚SpaceT.^ PYL
E/J
PL-CALTECH/NASAWhen moons leave
home they may
become ‘ploonets‘
An exomoon flung into
orbit around a star could
be a kind of mini planet