Difference between a sesamoid fracture non-union and bi-partite sesamoid sprain

I recently got a great question from someone who was watching one of the videos on sesamoid fractures.

Underneath the big toe joint, you have two little bones called sesamoid bones.
 
Sometimes you can get a fracture or crack in the bone that doesn't heal. Then it turns into what we call a non-union. 

Some people have sesamoids called "bi-partite" sesamoids. It looks like a fractured sesamoid. But its' normal. The two pieces are connected by soft tissue. But that soft tissue connection can become injured or sprained. 
 
What's the difference between a sesamoid fracture non-union and a disrupted bipartite sesamoid sprain? 
 
Well, that's what we're talking about today on the Doc On The Run Podcast.