What is plastic deformation of a metatarsal stress fracture in a runner?

Metatarsal stress fractures are something I talk about a lot because they are one of the most common reasons a runner has to stop running. 

One of the reasons you would stop running is that you do not want something called "plastic deformation" of the healing metatarsal. 

What is plastic deformation of a metatarsal stress fracture in a runner?

Well, that is what we're talking about today on the Doc On The Run Podcast.