GREY'S ANATOMY - "Walking on a Dream" - The Seattle Grace doctors are on edge when a new medical professional enters the hospital; Arizona struggles with the emotional and physical pain of a phantom limb; and while battling pregnancy hormones, an overly-emotional Meredith is confronted with her worst fear, on "Grey's Anatomy," THURSDAY, JANUARY 24 (9:00-10:02 p.m., ET) on the ABC Television Network. (ABC/KELSEY MCNEAL) ELLEN POMPEO, CHANDRA WILSON, SANDRA OH