Serious medical help for my puppy?

My lab puppy is 4 months old. about 3 weeks ago someone dropped him and when we took him to the vet they said it was a sprained ankle. he has been gradually getting worse. ive taken him to 3 different doctors now. his back legs aren't functioning and he cant walk. he wont even stand up to use the bathroom. They found fluid in his brain and they said he had neurological damage to his spine but is there any other explanation? they're not sure if they can do anything to help him. advice?