LONDON – After Rob Summers was paralyzed below the chest in a car accident in 2006, his doctors told him he would never stand again. They were wrong. Despite intensive physical therapy for three years, Summers' condition hadn't improved. So in 2009, doctors implanted an electrical stimulator onto the lining of his spinal cord to try waking up his damaged nervous system. Within days, Summers, 25, stood without help. Months later, he wiggled his toes, moved his knees, ankles and hips, and was able to take a few steps on a treadmill. "It was the most incredible feeling," said Summers, of Portland, Oregon. "After not being able to move for four years, I thought things could finally change." Still, despite his renewed optimism, Summers can't stand when he's not in a therapy session with the stimulator turned on, and he normally gets around in a wheelchair. Doctors are currently limiting his use of the device, made by Minneapolis-based Medtroni...