Awwww, poor Pasquale.
I'm sure he just twisted it chasing the birds. But it's always nice to hear confirmation from a vet that he's ok so I hope you get in soon. My dad also has a huge fenced in backyard and the dogs run like crazy over there together, I'm always worried he's gonna hurt himself! lol. Jackson came up limping in Jan. for what seemed like NO reason and it ended up being Lymes disease so he got put on an antibiotic and stopped within an hour, but in your case it sounds like he just injured himself!