Clinical and biomechanical measures of balance as fall predictors in ambulatory nursing home residents.

BACKGROUND: We evaluated the capacity of biomechanical and clinical measures of balance to predict future risk of recurrent falls in a cohort of frail, elderly ambulatory residents of 12 Tennessee community nursing homes.
METHODS: Baseline measurements of balance and other potential fall risk factors were obtained in 303 ambulatory nursing home residents. Balance measures included biomechanics force platform measurements of postural sway (area ellipse and mean velocity) and clinical measures, which included functional reach, Tinetti balance subscale (adapted from Tinetti's Performance Oriented Mobility Index), timed chair stands, and 10-foot walk. Residents who fell two or more times during follow-up (mean of 11 months) were identified from nursing home incident reports and nursing notes. The predictive value of the balance measures was evaluated by the incidence density ratio (IDR) estimated from proportional hazards models.
RESULTS: There were 118 recurrent fallers (54.2 per 100 person-years). Rates of recurrent falls increased with increasing quintiles of both the biomechanical and clinical measures of balance, with unadjusted IDRs (95% CI) per quintile change of 1.22 (1.07-1.39) for area ellipse, 1.12 (0.98-1.27) for mean velocity of postural sway, 1.29 (1.13-1.47) for the Tinetti balance subscale, 1.24 (1.08-1.41) for timed walk, 1.24 (1.09-1.42) for timed chair stands, and 1.12 (0.98-1.28) for functional reach. Controlling for age, gender, height, and weight did not materially affect the linear relationship between the balance measure quintiles and subsequent recurrent falls. However, after controlling for additional fall risk factors, only area ellipse of postural sway and the Tinetti balance subscale remained independently predictive of subsequent recurrent fall rates, with IDRs of 1.16 (1.02-1.36) and 1.17 (1.01-1.34), respectively. In an analysis where subjects were stratified by tertiles of each of these two measures, each measure appeared to independently predict future rates of recurrent falls. The independent predictive capacity of each measure persisted after controlling for other fall risk factors in a multivariate analysis with IDRs of 1.15 (1.00-1.32) for area ellipse and 1.15 (1.00-1.32) for the Tinetti balance subscale. Inclusion of both balance measures in a model with other fall risk factors to evaluate their relationship did not materially alter IDR point estimates of these risk factors.
CONCLUSIONS: In this cohort of frail, nursing home residents, both area ellipse of postural sway and the Tinetti balance subscale independently predicted risk of future recurrent falls. However, the predictive value of other independent fall risk factors on risk of future recurrent falls persisted and was not explained by these two measures. Thus, assessment of patient fall risk based on surrogate endpoints, for either research or clinical practice, may need to include multiple measurements.