91/2yr old Rottie needs surgery Had x-rays done on his knee ripped ligament?

He seems to put some weight on it but some days I know it hurts more then others, He’s always eager for are little walkshe weighs about 100lbs, He still gets around good but I don’t like seeing him in pain, 11mos. Ago he had pancreatitis with gastroenteritis that came out of now where and was in the hospital for five days. My family tells me to let it be and enjoy the time that I have with him but I don’t know. PLEASE PLEASE HELP..... Is there any thing outside of surgery that might be done, I'm afraid that he may not make it thought it, He had a hard time coming around after x-rays