14 year old cat with back leg dragging

Our 14 year old cat was not acting himself this past Thursday, I took him to the vet.  When the vet put him on the ground, his back right paw stuck out and he would not walk.  He was in pain when you touched his rear hindquarters.  They did an xray and found severe osteoarthritis in his hips.  Gave an injection of Buprenex SR and Depo Medro and sent us home.  The next day, it appeared he was constipated and had impacted feces in his anus.  I took him back to the vet. They repeated the xray and said his bowels were cleared from the previous xray and since he was able to perform bowel movements, the impacted piece would be better getting out on its own. Home we went.  I wanted  a second opinion on his condition because he was still in a lot of pain.  We went to a highly rated animal hospital nearby called VCA.  The vet said it is probably either the arthritis however, with the back leg laying out & not responding to pain meds or anti inflammatory, he said it could also be neurological of the spine for which only an MRI would show anything. He does not believe it's a blood clot because the toe pads are pink in color & when the vet manually extends the leg, there is no signs of pain.  The cat still has mobility in the leg.  Based on some knowledge from a vet tech, we got Buprenex oral prescribed since we were advised the SR formula is not as effective.  We also asked for appetite stimulant. On Tuesday, due to the Labor Day holiday, the vet is going to order Gabapentin but that will take time to receive since it has to be compounded into a dosage for the cat.  He is still in pain and not moving around much.  We have him in a crate with bedding and water.  When I last opened up the crate, he tried to get out so I decided to observe his abilities.  His back paw is still dragging but he walked slowly. I did not let him go far. I bundled him in a towel and let him lay on my chest while sitting on the couch as this is his favorite spot.  We are going to go back when the vet is open to do a blood panel and check his organs and other levels.  I've been reading the threads on this medical condition and it seems these symptoms can be anything from diabetes, thrombosis, low potassium to spinal issues.  His most recent blood work showed everything normal except high cholesterol.  We are stumped. 

I am so sorry you're going through this.  I have no words of wisdom, but send you big hugs.  It's so hard when our kitties get older.  He knows he's loved and that you're trying to figure it out. 

Thank you Stephanie. Your support is appreciated. It is hard. He's always had a lot of moxy and pizazz. This was sudden & out of the blue. Wishing you well.

With thrombosis, everything I've read indicates the leg would be cold because the blood stops flowing into it.  Since his pads are still pink, I think you can probably rule that out, especially since the Vet DID check for it also. 

WHEN was his most recent bloodwork?  Thinks can change rapidly in aging cats .  That being said, however, usually the things you mentioned don't affect just ONE leg the way you are describing.  Normally if the hindquarters are affected, it's BOTH back legs.  I wonder if he could just have a really bad sprain, which would NOT show up in an xray.  Obviously he has the arthritis, but I'm guessing that didn't occur overnight. 

As to the arthritis, here's a thread on it, and managing pain:  http://www.thecatsite.com/t/301292/...arthritis-onsior-buprenex-tramadol-or-adequan