What is the primary cause of bumblefoot?

[enggass]

Just want to know... Also, my birds run is made of 1" minus gravel/dirt. I plan on adding some sand to soften, but should this be a concern?
Steve

 

[Tala]

Staph infection that gets into a wound. Staph lives on the skin all the time (different strains for different animals I believe, you won't get it from your chicken), so you can't avoid that but avoiding every possible scratch is also pretty darn impossible.
It's just one of those things