Cronic lameness, no known cause

My Paint mare has been lame since this spring. She seemed perfectly sound when I got her. I took her to the vet right away and he said she was sound and healthy. The only thing I noticed in the first month was that the saddle always tipped a bit. However a month or so after I got her she started favoring her front left leg, and soon was "head bobbing lame". I put her on rest and kept an eye on her, thinking she pulled something, when it didn't get any better I took her to the vet again. He did flexion tests, which didn't show anything. He then numbed her leg in various spots until he found the lameness seemed to be in her front left heel. He then took x-rays, which didn't show anything wrong. He really didn't know why she was lame, so he decided that it was most likely the deep digital flexor tendon, and she must have pulled it. He had noticed that one of her hooves was slightly more "clubby" then the other. He told me to rest her for a month or two and it should be better. Well it didn't get better, so I brought her back in, and he told me honestly that he had no idea what it was. She now seems almost to be lame on the other leg, and I am at a loss. Any suggestions would be greatly appreciated!

Find a vet who is an expert in lameness.

We can only be 'armchair quarterbacks'.

A couple of thoughts and only because I just went through this. As with other opinions though, you need another vet opinion.

1. Ask your farrier about her feet. My TB has one club foot, underrun heels and a long toe. I went through about 5 months of a chronic but very mild lameness and finally gave up with getting hte vet out (he admitted he was stumped) and took the horse to an equine med center. The heels and toe issue caused a compression of the deep digital flexor which basically mimicked navicular syndrome. The x-rays did show some very VERy mild navicualr bone changes. He has been reshod with a heartbar shoe and 2 degree wedge with a square toe. He had the same thing, heel pain in both fronts. It has only been a week and there is already significant improvement.

2. You indicated a shift in lameness. As a precaution, have a Lyme test/titre pulled. Chronic, low grade lameness and shifting lameness are two symptoms. My horse did test positive though at a very low level. After consultation with the vet, we are holding off treatment for now and will retest in about 6 weeks.