Dynamic parameters of balance which correlate to elderly persons with a history of falls

Abstract

Poor balance in older persons contributes to a rise in fall risk and serious injury, yet no consensus has developed on which measures of postural sway can identify those at greatest risk of falling. Postural sway was measured in 161 elderly individuals (81.8y±7.4), 24 of which had at least one self-reported fall in the prior six months, and compared to sway measured in 37 young adults (34.9y±7.1). Center of pressure (COP) was measured during 4 minutes of quiet stance with eyes opened. In the elderly with fall history, all measures but one were worse than those taken from young adults (e.g., maximal COP velocity was 2.7× greater in fallers than young adults; p<0.05), while three measures of balance were significantly worse in fallers as compared to older persons with no recent fall history (COP Displacement, Short Term Diffusion Coefficient, and Critical Displacement). Variance of elderly subjects' COP measures from the young adult cohort were weighted to establish a balance score ("B-score") algorithm designed to distinguish subjects with a fall history from those more sure on their feet. Relative to a young adult B-score of zero, elderly "non-fallers" had a B-score of 0.334, compared to 0.645 for those with a fall history (p<0.001). A weighted amalgam of postural sway elements may identify individuals at greatest risk of falling, allowing interventions to target those with greatest need of attention.

Trial registration: ClinicalTrials.gov NCT00396994.

Conflict of interest statement

Competing Interests: DK has received grant support from Merck, Novartis, Pfizer, Amgen, Wyeth, Hologic; he has served as a consultant for Merck, Novartis, Amgen, Wyeth, GSK, Procter & Gamble, and has served as a speaker for Merck and Novartis. CR is a founder of Marodyne Medical. JM has received grant support from Novartis, Merck, and Eli Lilly and has served as a consultant or advisory board member for Amgen, Glaxo SmithKline, Eli Lilly, Novartis and Sanofi Aventis. This does not alter the authors' adherence to all the PLOS ONE policies on sharing data and materials.

Figures

Figure 1. A: ROC plot of COP displacement variable.

Sensitivity and 1-Specificity are plotted as the cutoff value is varied. The ideal location is in the upper left hand quadrant (1,0), where 100% of fallers are detected and 0% of non-fallers are identified (no false positives). The dotted line (line of no-discrimination) represents the location of a value with no predictive value (catches the same percentage of both fallers and non-fallers). B: Plot of chi squared value versus cutoff threshold. Values over 3.84 have a significance of p

Figure 2. Stabilogram of a healthy young adult (A) and an elderly subject (B).

The trace, collected over the four minute quiet-standing test period, represents movement of the center of pressure, in both the Medial-Lateral direction (side to side), and the Anterior-Posterior direction (front to back). Signs of poorer postural stability are evident in the aged subject, with a larger area of sway, as well as multiple excursions from center. As might be expected, with a longer path-length realized over the four-minute period in the elderly subject, peak sway velocities are also greater.

Figure 3. Box plots of Z-scores for maximal COP displacement (A), RMS of COP displacement (B), Maximal COP Velocity (C), RMS of COP Velocity (D), Median Frequency (E), Short Term Diffusion Coefficient (F), Long Term Scaling Exponent (G), and Critical Displacement (H).

All measures but median frequency were significantly greater in fallers than non-fallers. The non-faller group had a number of outliers which were not excluded from data analysis. *p

Figure 4. B-Scores of elderly subjects with and without self-reported falls.

The B-score is based on an “idealized” postural sway profile, as established by a group of young healthy adults (B-score of zero). Those with at least one self-reported fall in the prior 6 months had a B-score of 0.645, compared to those without falls who had a B-score of 0.334 (p