I had a problem with my chicken as well. In fact, the one shown in my avatar. Chunk was fine while I was working the coop then when I came back, a rooster had just hopped off her, he back was gouged to a pulp and she could not move. It was like she she had suffered a stroke or something. For a couple of months, she lived in a tote in my house, she could barely lift her head and could not use 1 leg. She would however, still be able to eat.
Then one day, I dropped a bit of organic unrefined coconut oil into her water (it was just scrap) and her situation improved dramatically. it was just a small piece of coconut oil but her condition improved so much. She stayed in the house for another 1.5 months and she's now back in the coop. She's still tentative on the leg but she hops around well and is able to hold her own well.
I'm no vet and my story is anecdotal but the coconut oil might be worth a try.
There are many kinds but the kind I used is supposed to be the best kind which is organic unrefined.
You should be able to get it at health food stores, amazon etc. You can use extras for cooking and as a skin moisturizer. Let me know what happens! I'm curious if it really helps because I had no control test!