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Ronald Klein was biking around his neighborhood in North Wales, Pennsylvania, in 2006 and tried to jump a curb. “But I was going too slow — I didn’t have enough momentum,” he recalled. As the bike toppled, he thrust out his left arm to break the fall. It didn’t seem like a serious accident, yet “I couldn’t get up,” he said. At the emergency room, X-rays showed that he had fractured both his…