injuries treated on an outpatient basis, of nursing home admissions triggered by fear of falling, and of activity limitations and disability owing to falls.

DETERMINANTS OF FALLS: RISK FACTORS AND CAUSES

Current prospects for the prevention of falls are uncertain, although several intrinsic and pharmacologic factors that are associated with an increased risk of falls have been identified. Many falls in the elderly are probably multifactorial, resulting from the convergence of several intrinsic, pharmacologic, environmental, behavioral, and activity-related factors. However, knowledge regarding the etiologic mechanisms of these risk factors and how they combine to produce falls remains limited. Perhaps even more limited is an understanding of situational and environmental factors that precipitate a fall in persons with predisposing characteristics. Situational and environmental factors may be among the most important determinants of risk in healthy older persons. Finally, a better understanding is needed of factors that affect the risk of injury and other adverse outcomes of a fall.

Intrinsic Risk Factors

Falls are a recognized marker of frailty and mobility impairment in the elderly. The presence and severity of functional disability is a useful indicator of the risk of falling in individuals and populations (Table 15-1). Data from the National Health Interview Survey's 1984 Supplement on Aging indicate that persons aged 75 to 84 who require help with activities of daily living are 14 times more likely, and those with limitations in walking, transfer, and balance activities are 10 times more likely, to report having two or more falls in the previous 12 months compared with persons with no limitations.43 The association of falls with frailty and functional disabilities in the elderly is also evident in the high rates of falls reported in nursing homes.93 The design of effective preventive measures, however, requires knowledge of treatable impairments and conditions that contribute to functional disability, frailty, and falls in older populations.

Normal gait and postural stability depend on the proper functioning of sensory, neuromuscular, and musculoskeletal systems. Limb proprioceptive and tactile input, visual input, and vestibular input are critical for maintaining the body's center of gravity within



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