Quote Originally Posted by dragondawg
Ask for a safer NSAID than Rimadyl. Although its more notorious for causing liver failure, Rimadyl can also cause Kidney failure. Presumably the dog is not on Prednisone as that medication can cause increased thirst and wee-wee accidents. In fact you might want to withdraw the Rimadyl given the possibility of kidney problems.

The kidney problems are very likely not related to the original lameness problem. Instead since Xrays did not find any problems, you need a referral to a specialist who has MRI equipment. An MRI would be able to pick up such things as a torn cruciate ligament. Such injuries can start in one leg, and as the dog shifts its weight to compensate, the second leg (knee) starts to develop a rupture. It's progressive and can come and go.

Your top priority is to have the kidney function checked. Again if on Rimadyl, withdraw the medication in case it's causing any kidney problems. If the kidney function is addressed and found to be normal, then you can follow up on the lameness, asking for a referral. GL.
I agree with two additions.

Drinking lots of water can also be diabetes. The blood work should show if that or the kidneys is the problem.

Regarding the limping - Not only could this be an ACL injury but I've heard of similar things happening with a leg out of joint. I can't think of the proper wording for it but there is a ligament that is supposed to rest inside a dished out area in the joint, and sometimes that can pop out of place causing limping and pain. If the animal can work it back in the limping would go away. Wished I knew the technical wording for it but that's the best I can do. I don't believe stuff like that shows on x-rays but only by feeling and manipulating the leg joint.

I agree that first priority should be to address the water hogging as that can be far more serious than the limping.

Keep us posted.