Boxer pup limb weakness

Question
Hi, we have an 11 week old male boxer pup who has had a rapid onset of rear leg weakness. At first he was a little unsteady and just looked stiff when standing or sitting, mainly in the rear legs. Over a 2-3 day period this has become a lot worse, he struggles to stand from sitting and can't stand from lying .. We have had x rays, bloods uncluding I think muscle enzyme tests, joint tap which appears normal also.. It seems, although hard to pin point that the joints are a bit tender to touch but he still seems to have good range if movement. Appetite and toilet behaviour is normal, no temp etc...
Any ideas, comments would be Appreciated!
Thanks

Answer
If the vet has run tests to determine any physical problems and cannot find any, then it must be neurological.

Also, it is a symptom of distemper, a symptom of parvo, etc.

That does not mean it is, however, he could have been born with a neurological problem or aquired the problem from an injury. Either way, you must see a specialist; a vet that specializes in neurological problems. (also, did the vet check his spine?)

Please let me know what the specialist finds in a follow-up.