The Taylor Spatial Frame
Photo credit: Smith-Nephews
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"On the very near horizon there
will be less obtrusive ways to do bone lengthening,"
predicts Dr John Birch, who presented a session on correcting
leg-length discrepancy at the annual meeting of the
American Academy of Orthopedic Surgeons in Chicago in
late March. For the orthopedic surgeon at Texas Scottish
Rite Hospital for Children in Dallas and former Ottawan,
the most interesting steps in that direction are the
Taylor Spatial Frame, a computer-aided external fixator,
and an internal telescoping rod called the ISKD nail.
Both are available in Canada, but neither is widely
used here, according to Dr Michael McKee, an ortho surgeon
at St Michael's in Toronto.
Both techniques require the surgeon
to cut the bone, and a lengthening device is then used
to gradually pull the ends apart. "The body keeps making
bone to fill the gap but you have to keep one step ahead
of it to make sure the bone doesn't congeal to the point
that you can't keep pulling on it," explains Dr Birch.
"Once you achieve the length you need, you lock it in
place till it's healed enough to tolerate the patient's
body weight." The usual rate of lengthening is 1cm per
month.
ON
THE OUTSIDE
Circular external fixation — developed in Russia
by Dr Gavriil Ilizarov in the 1950s — is the most
commonly-used method. It involves a series of rings
and struts connected to the bone with pins and wires
that are slowly tightened. "This allows you a great
deal of flexibility," says Dr Birch. "And because you're
doing it gradually there's a much lower risk of neurovascular
injury because you give the soft tissues a chance to
adapt."
The Taylor Spatial Frame is a variation
on the Ilizarov — with a twist. It comes with a
computer program that maps out how the deformity can
be corrected, using equations based on the Fibonacci
sequence. "The surgeon accesses the software on the
internet and feeds in the details of the deformity relative
to the rings he's applied," explains Dr Birch. "He's
then given a prescription of how to turn the rods to
get the correction he wants. It's quite an elegant thing."
From this, the patient is told how much to turn each
strut every day.
Much as they're impressed by the
technology, both Dr Birch and Dr McKee say they've decided
against using the Taylor device. "You're completely
dependent on the printout," says Dr Birch. "I'm not
comfortable giving up that much control — I'm a
bit of a control freak," he adds, laughing.
Dr McKee agrees. "The old school
— and I'd have to include myself there — would
be much more likely to want to know exactly what they're
doing," he says. "With the Taylor frame, the computer
takes over and you're not totally sure what's going
on until you get the final product."
"But for somebody who's not very
much used to external fixation there's a much better
chance of doing a good job with the program helping,"
notes Dr Birch. The Taylor is also much more expensive
than a classic Ilizarov.
HAMMER
IT HOME
"Internal fixation is a good technique when you have
relatively mild deformity and healthy tissue," explains
Dr Birch. "It's satisfying to the patient [because they
see an immediate difference], but you've done more trauma
to the limb and the implant increases the risk of infection."
The ISKD nail is made up of an
outer hollow and inner solid tube that telescopes. "With
the nail, the manipulation is done by rotational movements,"
explains Dr Birch. The ISKD comes with a little sensor
that monitors how much the rod is turning.
The catch is how you get it to
turn. "In ideal circumstances, the normal rotation that
occurs with walking will cause this to happen." But
not all patients are ideal. "Some patients will have
pain, so they can't or won't walk around." When that
happens, the only way to turn it is to grab it and turn
it manually, which is obviously pretty painful. For
that reason, Dr Birch says it only works when you have
"a highly cooperative patient who's going to try to
move the leg vigorously."
Dr Birch doesn't use this device
either, but he's excited about a similar one used in
Germany called Fitbone, which has a built-in motor that's
controlled remotely. "This is a huge advance because
the patient doesn't have to do anything but bring the
device to the sensor and then a little motor does the
work."
A
BIT OF A STRETCH
Dr McKee estimates that there are no more than a couple
of hundred Ilizarov procedures done each year in Canada.
Most ops are done on patients with a deformity, but
it's also occasionally performed for cosmetic reasons.
"I've done that a few times, mostly people with some
kind of syndrome, such as dwarfism. I even did a few
physiologically normal people who were just very short,"
says Dr McKee. "I don't have a whole lot of enthusiasm
for it, frankly. It's a very resource-intensive thing
to do and resources for this are already very limited."
He believes the risks just aren't worth it. "You can
take a normal short person and make them a miserable
tall person if you're not careful."
There's theoretically no limit
on how much a leg can be lengthened. "My personal record
is 17cm for one bone," says Dr McKee.
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