Mareks is possible I guess but if it lasted a month already then it would have to have been exposed to Marek's more recently (as opposed to catching it from a hatchery or wherever you got it from). Also you would need to separate the chick immediately, you probably should anyway because it might get picked on for being sick or injured.
Honestly if there were not a problem with the neck in addition to the leg, I would say go ahead and bring it inside and do some chicken physical therapy (chicken bicycle, chicken squats, chicken stretches, etc) because it probably got stepped on or something, but the bent neck is throwing me off.
Vitamin E would definitely explain the neck problem, but I haven't heard of it causing a leg to act funny. It is very possible that a vitamin E deficiency might be the cause of both problems, it's just that I don't know of a connection between that and the leg.
You could treat the chick with chicken PT for the leg and give it some vitamin supplements and hope that these two problems are unrelated. Most of the time if I notice a neck and leg injury at the same time, I find that the cause is usually neurological, which doesn't really make sense here because the chick lasted for a month with no other problems.
You might want to consider calling a diagnostic center to see what they have to say, or find a chicken vet. I live in CT and UConn has a diagnostic office that takes call-ins like this, I think most universities like that do. UConn's diagnostic number is (860) 486-3738. I'm sure they will take out of state calls, you might have to dial a 1 in front of the number or something.
