Help Sam my service dog w/surgery

My name is Vivian Stevenson and I need help with my service dog. For many years, I have done fostering of dogs with a number of rescues. Sam came to me at 10 months old because his owner didn't know he would get so big. Sam was what they call a foster failure as he reminded me of my very first Pyr foster so I kept him which turned out to be a good thing for me.  About four years ago, I started having trouble with my balance so I started to train Sam who was two years old to help me.  Sam has  been my service dog for the past two years as I have issues with my balance which cause me to fall.  Because I have fallen before Sam, I also have issues with panic attacks so having Sam with me eases those as well.
A couple months ago, Sam started limping occasionally and then more often.  After having it checked and xrayed, we have been nursing the knee along with anti-inflammatories and glucosamine, but it's getting worse as he limps all the time now.  Without Sam, I'm unable to go out without great difficulty and a lot of anxiety.  Despite his limping, Sam still insist on doing his job for me and going with me. But instead of standing next to me like he has always done, touching my leg to help steady me and comfort me, he will now lay down next to my feet, touching my ankle to let me know he's there.  Sam has an appointment with the vet to discuss when the knee surgery will need to be done, probably within the next two weeks.  My husband and I live on a limited income because we are both disabled and retired.  This fund will pay for Sam's surgery and to get him back on his feet to help me as I'm the one who does all our errands, grocery shopping, etc.  Having Sam means so much to me, to my ability to go places and take care of my husband, so any help you can give will be greatly appreciated whether it's a small amount or sharing his page.