Sparky needs surgery

Hey everyone we usually don’t ask for help with much.  But this time, we really need your help.  
Sparky needs surgery on his right knee and it’s more than we can handle on our own.  He has arthritis and his knee cap won’t stay in place.  We think his injuries came from who he was rescued from.  It’s almost unbearable to see him in so much pain, especially when it’s cold out.
Before Sparky was rescued, his owner kept him in a small box and starved him.  As you can see in the photo below, this is how he was found.  And in the main photo you can see how much he’s recovered and how much we love him.  Even after all he’s been through,  he’s a very forgiving, sweet and beautiful boy.  Any and all help is appreciated.