This is Jasper Junior - or JJ as he is often called. He is twenty-two years old, a gelded male or John mule and he's been retired for seven years after coming up lame after a hunting trip.
Let me preface this by saying it is not unusual for a veterinarian to not be able to identify exactly where a lameness is coming from. This is not because of lack of education by any means, but because lameness is different for every single horse and the causes could be a large number of things that need to be ruled out, and often are only ruled out after extensive, incredibly expensive tests. I've seen some of these tests and they are fascinating and sometimes extremely informative, but the average horse owner is not going to spend thousands of dollars on ultrasounds, CT scans, X-rays or surgery to pinpoint the cause of lameness in a family horse. It's just not feasible. So, I don't by any means think it is odd that there is no definitive veterinary diagnosis in this case.
What I first noticed with JJ is that his right hind end is severely atrophied and his left looks fairly normal. My first thought is to check his back and his illopsoas area for stress points and scar tissue. My concern is that if he had some sort of disk injury that compressed some nerves there is nothing I can do to really fix that, but even if that is the case, massage can help the atrophied tissue with increased circulation and if nothing else improve his comfort level.
Here is a photo of JJ from behind. That isn't shadows or light making it look like his right side dips down dramatically, it really does. I wanted to take a "before" picture so that I have something to compare to as I work on him.
I hope to head back over on Tuesday and this is my plan for our first day: Try to get some video of him walking, take some notes on where I'm seeing the most tension and where he seems the most stuck, and do a full palpation so I can note what I feel. Then I will make a plan for treatment - either once or twice a week depending on what I find that I can work on.