How long have you had them and have they been getting the BY from day one? If the legs were initially normal and this has been happening for the past few days, general deformity seems a safe rule out. My WH girl had a brief few days of going lame at one point when she was a little....she needed more BY then her significantly smaller Cayuga hatchmate. I seem to recall a thread somewhere in here about WH being particularly niacin deficient.....I toss this out there just to say Pekin are large birds so it's requirements may be higher than the average bird. If a boost in niacin is the ticket you can see improvement in just a few days.