If the vet is not 100% sure the ACL is torn, you might want to ask him about trying these injections 1X a week first. The name of the medication in the injection is ADEQUAN. It has worked for our Weimaraner more than once. The 1st time he had about 5 shots, the 2nd time I think it was 4. The last time he hurt his knee, he just had 1 & felt better.
He runs hard & stops fast & this is how he injures it every time.
He also takes TRAMADOL 50 mg 2 pills every 12 hours for the pain when he's hurting. He weights 78 lbs.