Osteoporosis, a loss of bone mass that comes with aging, makes the bones brittle and subject to easy fracture through falls or even without falls. An important part of preventing injury of older persons through falls is to diagnose for osteoporosis, and if it exists, treat it. Also, adopting a lifestyle that helps prevent osteoporosis is a key part of avoiding injury and mobility loss through falls and fractures.
See also, Osteoporosis:
MedlinePlus, National Library of Medicine, National Institutes of Health.