Some fans have wondered if it's because Jessica Capshaw, who plays Arizona, actually lost her leg in real life, especially as the amputation looks so realistic on screen. The answer to that is no: Jessica Capshaw's legs are both a-okay.
This plotline came out of showrunner Shonda Rhimes' desire to show the story of someone learning to live with their disability. You can read more about Shonda's thoughts on the plot here, and Jessica herself reveals how the show uses movie magic to make it look like she only has one leg here.
Grey’s Anatomy airs Thursdays at 9 p.m. ET/PT onABC.