Aw, man - sorry the news isn't better! Is Cutty having the TPLO or a different surgery? Also, I hope the surgeon let you know once one knee goes, the other is likely to follow (something like 80%, which stinks!).
But luckily, it is a very common procedure since SO many dogs tear ACLs so Cutty's surgery and recovery will hopefully be very smooth.
It sounds like your vet recommended surgery because the movement of the joint would eventually cause crippling arthritis. I know it's a hard thing to deal with since Cutty is 6.5 but I guess one way to look at it that torn ACLs and bad hips and things like that used to be a death sentence for dogs. Thanks to innovations in veterinary medicine, we are able to help maintain our dog's quality of life, or in many cases, give them a new lease on life. This is the way I tried to view everything we went through with Truman and Bentley (including the hit on the wallet).
If you have any specific questions, please let me know! Bentley had both knees done with TPLO but I know there are newer innovations now and Cutty's treatment might vary with his age.
Good luck Jenn - you're not alone!