Good spot, your right that that is one possibility Icemaiden, though in this case it is more likely to be related to age and/or a disturbance which has stressed the bird and caused damage while the egg was in the shell gland, the ridges are where the shell has then been repaired internally. I was reading that the incidence of ridged or 'body checked' eggs can range from less than 1% in flocks of 35 weeks old to up to 9% in flocks of 60 weeks, these birds are now around the 86 week mark and do have their problems, some with shell quality, some with wind eggs, we have an egg bound chicken at the moment which in all likelihood means she has got about another 3-6 months before peritonitis will claim her, it's all part and parcel of being an intensive layer unfortunately, the way I look at it though is every week they get beyond the 72 is a bonus for them.