mobility problems/arthritis

Question
I am having a puzzling situation with my girlfriend's bunny and have decided to look more into the situation.  First off, we've both been housing rabbits for several years and consider ourselves fairly experienced bunny parents.  About 2 weeks ago my girlfriend called me in the middle of the night and told me she heard a loud crashing noise and upon investigating it saw her bunny in his cage acting strangely and dragging his legs.  I came over (I'm an EMT so I have a little more experience feeling for abnormalities) and I began to palpate his rear legs.  He was definitely keeping weight off his left leg and it felt a little strange to me so I told her we needed to get to the vet once they opened.  We made the appt. and the doc (who is experienced in exotics and has an avian cert., etc.) did the palp and said he didn't feel anything broken, but he was keeping weight off it.  They gave us some medicam and said if it doesn't get better in a week bring him back for an x-ray.  He has shown very little improvement.  At some times he runs and moves fine, other times, he drags his leg around as if it's broken.  We took him back and they did a 10x12 radiograph of his back legs.  There they found nothing broken, but "mild" arthritis in his left leg and a healed, but previously unset fracture in his right.  He was a rescued rabbit and judging from the conditions described, he wasn't well cared for.  They said the previous fracture wouldn't have been the cause of his current problems since that had healed already.
My question is that although he has arthritis, why would this problem have such a sudden onset?  He seemed fine until she heard whatever loud noise woke her up.  Now he seems like a totally different bunny and I can't help but think there might be something else going on.  I've read some things about glucosamine, is that safe for rabbits?  Any suggestions on what else might be going on here??

thanks and sorry for the long description.

Answer
Dear Charles,

There are many possible causes of hind limb paresis in rabbits, and you can find an overview here:

www.bio.miami.edu/hare/paresis.html

In light of the bunny's history of trauma, it's not unreasonable to think that arthritis or a pinched nerve from an old injury could be the cause.  But don't let a red herring distract you from the possibility that this is related to a parasite known as Encephalitozoon cuniculi.  This is discussed in the article above.

The parasite can be treated with fenbendazole and/or ponazuril, but recovery from paresis will depend upon how much permanent neurological damage has already been done.  It's something to consider, and since both those medications appear to be relatively benign in rabbits (especially ponazuril), it might be worth trying to see if there is any improvement.

If you think you want to see another vet for a second opinion, you can find rabbit-experienced vets here:

www.rabbit.org/vets

Corticosteroids would be a last resort, as you probably know.  And it wouldn't hurt to try glucosamine.  Might not help, but it probably will not hurt.

I hope this helps for starters.  Please write back if you have more questions.

Dana