Dr. Rainer Kotz, an orthopedic surgeon at the University of Vienna, has found success by mimicking the body's processes. In the July 13 issue of Nature, Kotz and a team of researchers describe their latest creation: A novel leg implant for children who have lost bone from the knee following the removal of a tumor. As surrounding bones grow larger, this implant extends to provide more natural mobility.

Traditional bone implants, though effective in adults, are problematic in growing children. Because the size of the implant doesn't change, the child's uninjured leg is soon disproportionately longer than the injured one, impeding the child's normal body alignment and gait. In the past, doctors have developed extendible implants that could be manually lengthened during surgery. But that approach forces the children to undergo repeated, painful surgeries that cause extensive scarring.

Kotz says his device allows a greater range of motion than previous implants. And since the energy needed for elongation comes as patients walk, Kotz's device closely tracks normal leg growth.

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