If the pasture is going to cause him to be standing in wet grass or mud constantly I would keep him in the stall until the mud fever healed, otherwise it is not going to get any better. I would also try to figure out an alternative to turning him out in a swampy pasture---as there are worse...
My boy had the exact same symptoms, he has osteoarthritis in his hocks. So now he gets biannual hock injections and is as good as gold. However they are costly :/ FYI whatever you do don't waste your money on oral supplements, they have never been proven to be effective.