Integration of reginal shear measurements at the foot-ground interface during routine balance assessment of the elderly population

Background: Force-plate posturography offers a convenient way for quantitative assessment of postural stability in the elderly. However, studies focusing on routine balance assessment have usually not taken reginal shear distributions (i.e., arising from horizontal forces) into consideration. Research question: (1) Does plantar shear distribution differ between young and elderly subjects during upright standing? (2) How do the maximum plantar shear forces vary at different regions of the foot? Methods: The new reginal shear measurement (RSM) method can simultaneously capture the three-dimensional force distributions at regional plantar sites while subjects maintaining standing balance. The feasibility of the proposed method in characterizing the magnitude and distribution of plantar shear forces was tested in thirtytwo normal young and nineteen elderly subjects. Statistical analysis was performed using the independent samples t-test for both the continuous and ordinal variables. Results: For regional AP shear forces, statistically significant differences were found between the two groups for the toe region of the right foot and the midfoot of both feet. For ML shear distributions, statistically significant differences were found at nearly all plantar sites expect for the hallux and lateral metatarsal. The maximum increase in ML shear forces occurred in the toe region of the right foot, where the peak shear values were 113.16% higher than those of the young subjects. The peak ML shear occurred in the midfoot were averagely 83.19% and 70.57% higher in the elderly's left and right feet, respectively. Significance: The RSM method may offer unique solutions to identify functional decline in postural control of the elderly. The plantar shear pattern has potential to become an important parameter in evaluating one's balance performance during upright standing.