Thanks, @neetabeamie - I am soooooooo tired . . . .
It's also called bumblefoot. And you are right, it can be serious if not treated.
The first post in this thread has a very good explanation of how to treat it without cutting.
https://www.backyardchickens.com/t/807777/bumblefoot-new-ideas-on-treatment-with-pictures
And yes, niacin deficiency can cause leg problems. Usually it's good to supplement when they are young, But I feel it cannot hurt to try some. Either a tablespoon of brewer's yeast (brewer's yeast, not baking yeast, not winemaking yeast) per cup of food - or 150 mg of niacin per gallon of drinking water (plain niacin, not slow release or no-flush). If you use a B complex vitamin, use the amount of niacin as a guide (again, 150 mg per gallon of drinking water).
Please keep us updated.