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Expandable Prosthetics Help Children Grow

Howard Rosenthal, MD

October 07, 2019

As an orthopedic oncologist, I deal with highly complex health issues every day. My charge is to not only cure a patient of his or her cancer but to also try to make bones and soft tissues workable and functioning again.

Many of my patients are children with cancer in their bones, which places their limbs at risk for amputation. Not so long ago, these children either had high-level amputations or procedures that replaced the bone with a prosthesis or artificial bone within their limb. Doing this meant that because of their young age and potential for growth, they would require numerous operations throughout their childhood to lengthen the prosthesis. However, because technology has come so far, we are able to offer something better.

That “something better” is a noninvasive, expandable prosthesis for children. The prosthesis is not yet approved by the U.S. Food and Drug Administration, but is being used experimentally at select cancer centers. We are one of only a few facilities in the nation to use the device to reconstruct and rebuild the limbs of pediatric cancer patients.

The prosthetic device is surgically implanted and allows for attachment of all ligaments and tendons. This allows the surgeon to expand or grow the prosthesis in a noninvasive fashion by placing the limb in an electromagnetic field, which activates a gear mechanism creating growth. Within 16 to 20 minutes, a child’s arm or leg can instantaneously grow up to 4 mm (about 1/16 of an inch) and catch up with the other limb. We can lengthen the limb as many times or for as long as necessary, based on the patient’s growth. Patients say there’s no added stress on their muscles or tendons and that they can rarely tell the difference between the prosthetic limb and the real one.

Consider a child of age 5 to 9 who has bone cancer. We face 2 dilemmas:

  1. Cure the cancer
    With metastatic cancer, reconstruction of the limb is a primary goal, but the reconstruction efforts may interfere with the cancer treatment and healing process. Finding a way to restore the limb without getting in the way of therapy is a challenge. (A metal plate, for example, may be problematic for, and interfere with, MRI and CT scans.) Matching the biological aspects of reconstruction with the potential for future therapy is a task we must consider. Thus, carbon fiber implants allow us to better visualize the part of the body that is reconstructed, even with MRI and CT scans.

  2. Provide for growth
    Children who lose limbs often experience disruptions in their growth or damage to their growth plates. Any restoration has to allow for growth as a child ages.

With the compassionate-use permission of the FDA, we have completed 30-plus procedures that involve the expandable prostheses with amazing results. The function and appearance are very normal. The device is constructed of titanium and a high molecular weight polyethylene, and includes a very small but powerful motor. The prosthesis is temporary and will convert to a long-term prosthetic replacement when the child reaches adulthood. By that point, we expect the patient to be cancer-free with no worries about future treatment.

These treatment advancements are so exciting. It’s an opportunity to help create a modern-day “Bionic Woman” or “Six Million Dollar Man.” I find it very gratifying to do cancer research, but I was always interested in bioengineering and biomechanics. I’m pleased to be able to help cure patients of cancer and help them lead normal, high-functioning lives again.

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