Rates of hip fractures, an often devastating consequence of osteoporosis, have been steadily falling for two decades in Canada, a new study finds. And a similar trend occurred in the United States, researchers found. But it is not clear why. Drugs that slow the rate of bone loss may be part of the reason, but they cannot be the entire explanation, osteoporosis researchers say. And although experts can point to other possible factors — like fall prevention efforts and a heavier population — the declining rates remain a medical mystery. The new study, published Wednesday in The Journal of the...