Both my dogs, Bandit and Cody, were 13 to 15 years old and were suffering with rear leg problems.  
We had been giving both of them expensive joint supplements for many, many years.   
Then our vet suggested Metacam.  
Within two weeks both animals went into an ambulatory decline, much worse that they had been.   
One started falling down the stairs and neither wanted to eat their food laced with Metcam and mixed with some tasty canned dog food, not their normal fare.   
They got worse and we stopped the Metacam. 
One died two weeks later, we did not have the vet do a necrotopsy.   

After three weeks or so, the other dog, off of the Metacam, has recovered his balance and back leg coordination.  The Metacam may have had a hand in the problems of both dogs. 

 Gary 

Dallas , Texas