Miniature Silky knuckling over on ankle

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I have a Minature Silky who started knuckling over on his right ankle about a month ago. He is 1 1/2 years old. I had a veterinarian look at him and he thinks the pain is coming from his elbow. Now he is starting to do it on his left ankle, but not as bad. I was wondering if anyone here has had a similar experience or might have an idea of what is going on. I realize he is overweight and he got into some horse cookies just before this happened, but I don't think it is laminitis.
Any help would be greatly appreciated
Thanks
Terri