The personal costs are far greater. About 20 percent to 30 percent of patients die within a year following a hip fracture and, the researchers reported, “Of those who survive, many do not regain their pre-fracture level of function. About 50 percent of patients with hip fractures will never be able to ambulate without assistance and 25 percent will require long-term care.”

A number of factors may have contributed to the downward trend in hip fractures that ended in 2012, according to Dr. Ethel Siris, a co-author of the new study and director of the Toni Stabile Osteoporosis Center of the Columbia University Medical Center in New York.

“The population may be getting healthier, people are doing more exercise and may be more careful about falling,” she suggested in an interview. But most likely a leading factor, she and her co-authors believe, was the introduction in 1995 of the drug Fosamax, a bisphosphonate that slows or prevents the loss of bone density, resulting in stronger bones.

Fosamax is now available generically as alendronate, and has been joined by several other medications capable of promoting stronger bones. However, Dr. Siris said, “There is clearly a treatment gap. Prescriptions have fallen off, and even when people at risk are offered medication, they are refusing to take it.”

Millions of prospective patients who could benefit from bone-preserving drugs are now afraid to take them. The fear probably has its roots in overly aggressive marketing and doctors who overprescribed bisphosphonates for every patient in the beginning stages of bone loss, a condition called osteopenia, with treatment often continued years longer than now considered appropriate.

Then in the early 2000s, alarming news reports began to appear linking extended use of bisphosphonates to two uncommon bone problems: a very rare fracture of the femur and an even rarer condition called osteonecrosis of the jaw. A fear of these complications resulted in more than a 50 percent decline in bisphosphonate use from 2008 to 2012, Dr. Khosla said.

At the same time, Medicare reimbursements for bone density tests were sharply reduced, and doctors who did them in private offices could no longer afford to, which limited patient access and diagnosis and treatment of serious bone loss despite major improvements in treatment guidelines, Dr. Lewiecki said.