Strange lameness

[Amanda Perez <APerez@hldi.org>]

  I recently came across a very nice looking mare for sale who is not sound
for riding.
I wrote the owners asking about the nature of her unsoundness, and got this
reply:

> >  She seems to have a problem in her back, but the vets haven't been able
> > to find it. What happens is that when she is being ridden she bunches up
> > her body and then her rear leg, when it is extended out, will almost go
> > out from under her. It looks a lot like bad stifles (patella) but it
> > isn't. Her stifles have been x-rayed and they are clean. She has been
> > through numerous tests and we have tried everything from rest to
> > accupuncture, to massage, to different shoeing, different saddles, no
> > saddle, injections, etc, etc, and nothing works. She is perfectly fine
> > in the pasture and runs around like all the other horses. To put more
> > money into tests is no longer possible, and since she is sound unless
> > someone rides her, being a broodmare is the best option at this point.

They said it was first noticed when the owner begand riding in the spring
after the mare had not been ridden
all winter, so they don't know how sudden the onset was.

Any ideas?  I am considering her as a brood mare, but don't like the idea 
of buying a lame horse without knowing the exact cause of the lameness.