Henry needs a new Knee

Hi, I'm Brenda Henry's mom; please meet Henry, he is 8 years old. Henry is my forever friend and protector. He is a shelter rescue. Henry needs a new back right knee. He injured his ACL on Nov 1st 2015. We have tried several treatments, therapies, that just cannot fix Henry, he needs a new knee. We have met an extraodinary surgeon Dr. E; who is willing to do Henry's much needed TPLO surgery with Arthroscopy at a reduced rate. This is why I am asking for the $4,000.00. I do not have the $ 4,000.00 dollars to give Henry what he needs. If he can, he runs 3-legged, he has difficulty with stairs, at times he whimpers when he has to go to the bathroom. It is distressing to watch him hobble around. I'm trying to keep him as comfortable as possible, with my Vet. Dr. Andrea's help.  Henry is a wonderful dog, with a "softie spirit" and a coat to match. He truly has the softest hair I have ever felt.
 My manager has given me the time off of my job to recover Henry. If I am able to raise the money for Henry we would like to schedule his surgery for the week of Dec 20th 2015. This would be Henry's best Christmas gift-to be able to eventually run again, go up and down stairs comfortably, to be able to go to the bathroom without whimpering or crying, to not be in pain or so uncomfortable.
 I feel horrible as a Mom to Henry; that I cannot afford to provide this for him. Currently, my financial circumstances gives us barely enough to live. I cried trying to compose a letter to the surgeon asking if he would consider lowering the cost of the surgery. I cried when I asked my manager if I could possibly have the time off to recover Henry; because I cannot afford to have someone come to the house to help with his cares.
 It is difficult to put into words, the amount of emotion I have; in how gratefully thankful we would be, if Henry could get his new knee. It is  truly humbling to ask for help for my forever friend and protector. Anything that is given would be greatly (beyond words) appreciated.