If you are certain that the amount of table scraps you give would not have interfered with the general basic amount of layer feed necessary for the birds then I have been looking at possible other sources of substance to interfere with calcium absorption...there are many ,however you might consider the following: Do you have limestone in your runs...do you have a well ... have you fertilized (see below) in a place where your chickens free-range? (see link below) it also might not be from you but from the person you got them from...so difficult to figure out sometimes particularly when necropsies often can only point out the findings but not give the cause....
http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/211000.htm
(excerpt...please go to link and read the rest)..."...Toxic quantities of fluorides occur naturally, eg, certain rock phosphates and the superphosphates produced from them, partially defluorinated phosphates, and the phosphatic limestones. In certain areas, drinking water from deep wells may contain high levels of fluorides. Volcanic ash may be high in fluoride. Wastes from industrial processes, fertilizers, and mineral supplements are the most common causes of chronic fluorosisFluoride binds to Ca2+, Mg2+, and Mn2+, acting as a direct cellular poison (including bacterial cells, hence its use in dental hygiene). At high levels most fluorides are corrosive to tissue.
In bone, fluoride binds calcium and replaces the hydroxyl groups in the mineral part of bone, which is mostly hydroxyapatite. In teeth developed during fluoride ingestion, the enamel is less soluble (protective) and more dense (brittle, if excessive). In addition, faulty mineralization of teeth and bones occurs
when excessive fluoride interferes with intracellular calcium metabolism and damages ameloblasts and odontoblasts........................
Casual observation of affected animals may suggest chronic debilitating arthritis; osteoporosis; or deficiency of calcium, phosphorus, or vitamin D. Lameness in advanced cases may be wrongly attributed to an accident. "