Growing Bones for Growing Kids After Cancer Surgery

—June 21, 2010 -- Morgan LaRue, an athletic nine-year-old from Lovelady, Texas, came home from school complaining of a knee ache. While small aches seem normal for active kids like LaRue, the pain persisted for nearly three weeks, and steadily grew worse.

When Morgan's parents took her to see a pediatrician, an X-ray showed that she had a tumor in her knee. Just before Christmas 2009, Morgan was diagnosed with osteosarcoma, a rare form of bone cancer deep within her leg.

Treatment for osteosarcoma often involves surgery to remove the cancerous tumor, usually followed by a year of chemotherapy. Doctors had to remove a portion of Morgan's bone in her upper leg. But according to Dr. Lisa Wang, LaRue's doctor and pediatric oncologist at Texas Children's Cancer Center in Houston, treating the cancer is just the beginning.

"Osteosarcoma often occurs in the long bone, often in the ends of the long bones, which is where the growth plate is," said Wang. "So if you have to treat that, or have surgery to remove the tumor, you often affect growth."

In fact, once the tumor is removed, part of the bone is replaced with prosthesis. But many parents who are faced with the decision implanting prosthesis for their growing child have to face the risk of potentially limiting their child's growth.

"The difficult thing for Morgan, who has a lot of room to grow is that, after surgery, she could potentially have uneven leg length, very uneven leg length," said Wang.

Dr. Rex Marco, an oncologic orthopedic surgeon at Texas Children's Hospital and the University of Texas Health Science Center at Houston who operated on Morgan, said the usual solution to allow leg growth is more surgery.

"You do a separate operation every 4 to 6 months and you lengthen the prosthesis," said Marco.

But because Morgan has many more years of growing, she could face an additional six surgeries. So instead, Marco and a team of surgeons implanted a new cutting-edge device that would save her additional procedures. Surgeons implanted a prosthesis that can be lengthened using a magnet outside the body, so that it slowly extends as Morgan grows.

Although the device is still waiting for U.S. Food and Drug Administration approval, about 15 patients currently have the prosthetic device implanted, said Wang.

A tiny gear box and a magnet are located inside Morgan's prosthetic bone. Doctors place Morgan's leg in a donut-shaped housing where there is another magnet. When the two magnets meet, the tiny gear inside Morgan's leg powers on and starts to turn, and Morgan's leg grows. Every four minutes that Morgan's leg is in the donut-shaped device, her leg grows a millimeter.

Bone Cancer Advance: Prosthetic Bone that Grows

And Morgan said she feels no pain through the process. In fact, during her first lengthening session, Morgan played a video game.

Morgan has about a decade left of growing and her prosthetic leg will be able to handle her growth, said Alec Macknight, an implant design engineer for Stanmore Implants, manufacturer of the magnet extender.

"There'll be enough growth capacity in the implant to get her out to her full height," said Macknight.

Morgan said she hopes she will soon be able to "run and jump and play," with her leg. And, according to Macknight, Morgan's implant will remain durable long after she stops growing.

"She can go play basketball and ride a bike," said Macknight. "She can live as full of a life as she can hope to."