In a Dec. 18, 2012, photo provided by Johns Hopkins Medical, a surgical team at Johns Hopkins Hospital in Baltimore works on a double-arm transplant for U.S. Army infantryman Brendan Marroco, 26, who lost all four limbs in Iraq. The transplants are only the seventh double-hand or double-arm transplant ever conducted in the United States. The infantryman was injured by a roadside bomb in 2009. (AP Photo/Johns Hopkins Medical)

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In a Dec. 18, 2012, photo provided by Johns Hopkins Medical, a surgical team at Johns Hopkins Hospital in Baltimore works on a double-arm transplant for U.S. Army infantryman Brendan Marroco, 26, who lost all four limbs in Iraq. The transplants are only the seventh double-hand or double-arm transplant ever conducted in the United States. The infantryman was injured by a roadside bomb in 2009. (AP Photo/Johns Hopkins Medical)