Effects of prosthetic ankle stiffness on adaptation to uneven terrain in individuals with unilateral transtibial amputation

Background

Uneven terrain poses significant locomotor challenges for individuals with unilateral transtibial amputation, affecting both gait kinetics and kinematics. Moreover, prosthetic devices are often prescribed for level-ground, although optimal device characteristics, such as stiffness, may vary depending on the terrain.

Research question

This study evaluated the interactions between prosthesis stiffness and walking surface height variability on step characteristics and joint mechanics.

Methods

Nine individuals with unilateral transtibial amputation participated in the study. Participants walked over a modifiable uneven terrain walkway to create even, low variability, and high variability terrain. On all terrains, participants used ankle-foot prostheses of three different stiffness levels: soft, medium, or stiff. We recorded gait kinetics and kinematics using two in-ground force platforms beneath the walkway and a motion-capture camera system.

Results

Terrain variability and prosthesis stiffness affected multiple biomechanical measures, but did not demonstrate any interaction effects between each other. Terrain influenced step parameters such as width, length, and variability measures, while device stiffness affected mean step width and length. Terrain and device stiffness did not significantly affect joint moments or positive joint work. However, stiffness affected the difference in peak ankle and hip moments between the affected and unaffected limbs. Terrain and stiffness effects were present in negative ankle and hip work measures.

Significance

On average, individuals with amputation exhibited relatively small changes in joint dynamics when walking on uneven terrain compared to level ground. Additionally, device stiffness had only minor effects on gait outcomes in response to changes in surface. These results suggest that varying ankle stiffness may not be an effective strategy for reducing joint loading or improving gait symmetry during uneven terrain walking.