Magnet-powered Bone Lengthening Device at Stanford Children’s Health Saves Kids Pain, Infection Risk

* 18-year-old Andrew Hirsch of Walnut Creek, California had more than
an inch added to his femur; knows from experience how new device
improves on old bone-lengthening techniques.

STANFORD, Calif.–(BUSINESS WIRE)–Orthopedic surgeons have developed a new device that reduces the pain,
scarring and infection risk associated with lengthening a leg bone. It
replaces an awkward external brace, which must be attached outside the
leg using pins through the skin, with a sleek, magnet-powered
telescoping rod that is bolted entirely inside the bone.

“This device is a big step forward for kids with discrepant leg
lengths,” said Stanford
Children’s Health
orthopedic surgeon Scott
Hoffinger, MD
, who has used it in seven patients, including the
first-ever child in Northern California to receive the new implant.

To lengthen a bone using either the old or the new device, a surgeon
saws crosswise through the bone and braces the sawed ends one millimeter
apart. The body grows new bone into the gap. The patient adjusts the
brace to move the bone ends half a millimeter further apart, twice a
day, until the bone reaches the desired length. Bracing continues until
the bone has hardened.

Now, instead of pinning a patient’s leg into a bulky external brace,
surgeons can accomplish the same thing by placing a small telescoping
rod inside the bone’s shaft to brace and extend it. The implant contains
a magnet-powered motor. The patient holds a compatible magnetic motor
against the leg for twice-daily, six-minute lengthening sessions.

“The biggest advantage is that we can lengthen a child’s bone without
having to pierce his or her skin and muscles for months with an external
fixator,” said Hoffinger, a clinical associate professor of orthopedic
surgery at the Stanford
University School of Medicine
and Lucile
Packard Children’s Hospital Stanford
. “It’s more comfortable for the
patient both physically and psychologically to avoid having a big frame
outside their leg with pins going through to the bone.”

The external frame is still required in cases where a leg bone needs
straightening, such as when a child’s foot is aligned at the wrong
angle. However, the new, magnet-powered internal device will work for
most children with different-length legs. Leg-length discrepancies may
occur because of congenital conditions that cause problems in bone
growth, fractures that heal crookedly, and tumors or blood vessel
disorders that affect the bone’s growth plates.

No one better understands the advantages of the magnetic implant than
18-year-old Andrew Hirsch, one of the few patients to have had his leg
bones extended using both the old and new techniques. Andrew was born
with fibular
, a disease that caused his right leg to be shorter than
his left and to grow very slowly. He had the old-style external fixator
used to lengthen the leg’s lower bones by almost three inches in 2010,
when he was 13. But a few years later, after a growth spurt, his legs
were again uneven. By then, Hoffinger had begun using the internal
device in other patients and thought it would be a good fit for Andrew’s
needs. In 2014, at Stanford
Children’s Health Specialty Services – Emeryville
, he explained how
the new technology could add more than an inch to Andrew’s right femur.
“I was amazed about how much the technology for this kind of stuff had
evolved in four years,” Andrew said.

When Andrew’s lower leg was lengthened with the old, external fixator,
the process was slow and painful. The pins going through his skin and
muscle tugged with every bend of his knee, and his ankle and foot were
immobilized in a gigantic horseshoe-shaped brace. The pin sites were
prone to infection. Lengthening took three months, and he was on
crutches for another three months while his new bone hardened. The
fixator required four surgeries to remove. Andrew missed a lot of school
and his favorite sports: baseball, competitive swimming, skateboarding
and water polo.

When his femur was lengthened with the internal rod, everything was

“The fact that there was nothing on the outside of his leg after he
recovered from the initial surgery was huge,” said Andrew’s mom, Luann
Hirsch. “It really saved us a lot of hassle, because we battled
infections the entire time with the external device.”

Instead of the wrenches he had used to expand his external brace, with
the magnetic implant, “I had a little ‘x’ drawn with sharpie on my leg,
placed the external magnet on top of it, flipped a couple of switches,
and grew half a millimeter twice a day,” Andrew said. “And the pain was
way more low-key.”

His right femur was lengthened 37 mm, almost an inch and a half,
requiring five weeks of twice-daily adjustments. Because the rod that
holds the magnet is quite strong, Andrew didn’t have to wait for the new
bone to harden to begin using it; instead, he could walk on his right
leg soon after the lengthening was complete.

“When we x-rayed Andrew’s leg during the process, we saw a gap between
the two ends of the bone, the rod inside the bone, and wispy layers of
bone being formed around the rod, maturing and getting solid,” Hoffinger

The magnetic motor in Andrew’s leg was removed January 21 at John
Muir Medical Center, Walnut Creek
. (Stanford Children’s Health and
John Muir Health are partners in bringing comprehensive children’s
specialty services closer to home for families in Contra Costa County
and surrounding communities.) It was his easiest journey to the
operating room yet: The set of three simple procedures was completed in
one day and required only a one-night hospital stay. He was walking
again three days later, and everything looked good when Hoffinger saw
Andrew for his follow-up visit at Stanford
Children’s Health Specialty Services – Walnut Creek

The magnet-powered device will soon help many more kids walk easily,
Hoffinger concluded. “The new magnetic device allows us, as surgeons, to
be less disruptive to kids’ lives,” he said. “Andrew has so many plans
for the future. It’s great to know that his leg won’t be holding him

About Stanford Children’s Health and Lucile
Packard Children’s Hospital Stanford

Stanford Children’s Health, with Lucile Packard Children’s Hospital
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Lucile Packard Children’s Hospital Stanford
Robert Dicks,