Gait Effects of Unexpected and Coronally-Uneven Terrain on Healthy Adults

Abstract

In the United States, falls are the number one cause of death and injury in adults over the age of 65. Many of these falls occur in the mediolateral direction and are attributed to extrinsic factors, such as uneven terrain. This study explored the stability effects and biomechanical adaptations of 10 healthy adults during ambulation over unexpected and coronally-uneven terrain. Experiments were conducted on a custom built walkway with an integrated disturbance device that was nominally flush with the walkway, but could also produce unexpected 15° inversions and unexpected 15° eversions. Unexpected eversions had the largest destabilizing effect on participant gait, as measured by both the range of coronal angular momentum and the minimum inclination angle. The disturbed limb played a role in maintaining stability, as suggested by the time integral of the external coronal moment it provided to the body not being equal between all conditions. Contributing to the corrective moment of the disturbed limb were the coronal moments provided by the hip and ankle strategies, whose time integrals were also not equal between all conditions (expected flush, and unexpected inversion/eversion). A multi-segment foot model revealed asymmetric kinematic adaptations to the uneven terrain that could be related to anatomical features. The ankle joint (comprised of the subtalar and tibiotalar joints) demonstrated more adaptation in the inversion than the eversion condition, as measured by the amount of inversion or eversion, respectively, of the hindfoot relative to the tibia in early and late-stance. By similar metrics, the midtarsal joint (comprised of the transverse tarsal and tarsometatarsal joints) demonstrated more adaptation in the eversion than the inversion condition. Kinetic adaptions of the ankle and midtarsal joints were significantly different between each of the conditions, but were not different for the grouped metatarsophalangeal joints. Like the disturbance itself, kinetic adaptations of the ankle and midtarsal joints were approximately equal and opposite for the inversion and eversion conditions. Clinically, the findings from this study suggest a sufficient coronal range of motion in the ankle joint is important for maintaining stability when ambulating over unexpected and coronally-uneven terrain; therefore, its preservation should be considered for certain orthopedic and prosthetic interventions as it may reduce the risk of patient falls.