Urgent: Rabbit unable to sit on hind end

Question
I am a rabbit owner of  over 15 years and I have a male rabbit that was rescued 5 years ago that I identified as a New Zealand but i am unsure of his exact age and if it would have anything to do with his current problem.

As of over a week ago he started having problems with moving his hind legs and now he primarily uses his front legs and pivots on his back legs to move around which he doesn't due much since it tires him out, and the rest of the time he lays on his side (always lays on his right). He does have feeling in both back legs and moves them when he gets up, but won't put his weight on them.

I took him to the vet after 3 days of these symptoms even though he was still eating and drinking, I was hoping it would be a fixable physical ailment since there was no trauma and he didn't appear to be in pain.

After examination and an X-Ray  he thought it might be a bone cyst (though he wasn't sure) and said the bone could break easily. Also upon examination he discovered one of his testicle was swollen but not overly red. This had me questioning if there was some kind of bacterial issue that caused some paresis to his hind legs (primarily the right that he doesn't move much). The vet suggested i give him a dose of Metacam once a day for 5 days and some added calcium to his diet (1/4 a tab of Tums). The last dose was two days ago and there was no change during or now for that fact.
Though as of yesterday he does have a problem urinating on his own and will only due so when i pick him up or hold him at an angle. And because of his mobility seeming to lessen i've been giving him water in a dropper so I know he's drinking.

If there are any questions to this situation please let me know
If you can give me any suggestions to help him I would really appreciate it.

Thanks,
Mariel, OH

Answer
Dear Mariel,

Please read this immediately:

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

and especially the linked article by Dr. Susan Brown.  There are many reasons for paresis, and one of the most common in rabbits of this age is Encephalitozoon cuniculi, a microsporidian parasite.  This can be treated with panacur and/or ponazuril.  The sooner this is diagnosed and treated, the better the chances for recovery.  But some bunnies remain unable to use the back end.  If this happens, don't despair.  A bunny like this can live a completely happy and full life:

http://www.rabbit.org/faq/sections/disabled.html

and more here:

http://search.atomz.com/search/?sp-a=00062824-sp00000000&sp-q=disabled

You can find a rabbit-savvy vet here:

www.rabbit.org/vets

Hope this helps.

Dana