Article by: Dennis Douda WCCO – TV March 30, 2011 – 5:48 PM MINNEAPOLIS (WCCO) — When high school gymnast Natalia Merrifield hyper-extended her knee, it took all the spring out of her step. That is not good when you’re the two-time defending state champ on vault and you cannot even stand as tournament time nears. Yet, Merrifield bounced back. She credits rehabilitation with Dr. David Stude and five days of therapy with a high-tech device Dr. Stude has great faith in. The OrthoCor Active Knee System targets the joint with mild heat and a pulsed electromagnetic field. “The research…