Reduced Medial-lateral Stability While Walking May Increase Side-fall Risk

Abstract

Most injurious falls among older adults occur while walking and the majority of hip fractures occur with a fall to the side. Stability while walking is particularly challenging because it requires controlling the position and velocity of the whole body center of mass (COM) within a constantly changing and moving base of support. With age, most older adults develop strategies such as reducing walking speed and stride length and increasing stride width to enhance mediolateral (ML) stability. However, older adults who fall to the side exhibit decreased stride widths while walking compared to “other-directed” fallers and non–fallers. This may place the COM closer to the outside edge of the supporting foot, hence closer to a sideways loss of balance leading to a fall. PURPOSE Our aim in this pilot study was to determine if the distance the COM is from the outside edge of the supporting foot while walking (a distance we call the ML safety margin) is smaller in people with a history of side falls compared to non-fallers and “other-direction-fallers”. METHODS Three young women (26 ± 2 yrs) and 3 older women (one side-faller, one other-direction-faller, and one non-faller; 75 ± 5 yrs) performed a series of 10 walking trials at their preferred speed over a distance of 7.6 m. All subjects' walking patterns were recorded using an optical motion capture system and the estimated spatial positions of the body's COM and lateral border of each foot were computed over the course of each trial. The ML safety margin was computed for each step as the minimum ML distance from the COM to the outside border of the foot while the foot was on the ground. RESULTS The older side-faller exhibited the smallest average ML safety margin (73.8 mm), as compared to the younger individuals (81.04 ± 5.84 mm, the non-faller (80.1 mm), and the other-direction-faller (85.4 mm). While these data are insufficient to perform sophisticated analyses, the trends support our hypothesis in that the side-faller has the smallest mediolateral safety margin, the value of which falls outside the 95% confidence interval of the mean safety margin of the young adults. CONCLUSIONS A smaller safety margin may contribute to reduced ML stability and an increased risk of side-falls and subsequent hip fractures.