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Hidden, magnet-powered telescoping rod makes bone-lengthening easier

Andrew HirschOrthopedic surgeons recently developed a new device for lengthening kids' bones that greatly reduces the time, pain and infection risk that patients face. It's appealingly space-age: a telescoping rod that hides inside the bone and expands with the help of a magnet-powered motor.

Perhaps no one understands the advantages of the telescoping rod better than Andrew Hirsch, an 18-year-old from Walnut Creek, California, who has had both the old and new devices used to lengthen his right leg. His medical odyssey finished in late January, when Andrew, shown above at a check-up, had the magnetic motor taken out of his leg.

Andrew was born with a condition called fibular hemimelia that caused his right leg to be shorter than his left leg and to grow slowly. In early childhood, he wore shoe inserts that made up the difference. But by 2010, when he was in seventh grade, the discrepancy was almost three inches. Orthopedic surgeon Scott Hoffinger, MD, recommended a months-long procedure to extend his lower right leg. In surgery, Hoffinger sawed the bone through crosswise, then held the ends of the bone a few millimeters apart with an old-style bulky brace that pierced Andrew's skin and muscle. The bone ends were gradually moved further apart and his body filled the gap with new bone.

By the time he was 17, Andrew's femur also needed lengthening. But this time, Hoffinger could offer the magnet-powered rod. A recent story I wrote about the innovation explains the difference:

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 different.

“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.”

Andrew - side-by-side legThe side-by-side image here really tells the story. Whereas the old device, on the left, looks really uncomfortable, you can't even see the new device without an X-ray. And, if you look closely at that X-ray, there's an intriguing detail: In the gap between the two ends of the bone, wisps of new bone are solidifying.

“The new magnetic device allows us, as surgeons, to be less disruptive to kids’ lives,” Hoffinger told me.

Previously: From post-WWII Russia to 7-year-old Gianna Brown, a limb-lengthening method evolves, How orthopedic surgery straightened out one man's life and 6-year-old Palestinian boy learning to walk after treatment at Lucile Packard Children's Hospital Stanford
Photos courtesy of Lucile Packard Children's Hospital Stanford and the Hirsch family

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