The Effect of Prosthetic Ankle Dorsiflexion Stiffness on Standing Balance and Gait Biomechanics in Individuals with Unilateral Transtibial Amputation

Introduction Modular prosthetic ankle components have been shown to improve walking in transtibial prosthesis users, but they may reduce stability during standing. Therefore, the stiffness of the prosthetic foot-ankle components may need to be appropriately tuned to provide a balance between walking mobility and standing balance. The present research investigates both concepts to improve our knowledge about how prosthetic ankle stiffness influences standing and walking performance. Methods Ten individuals with unilateral transtibial amputation and categorized as minimum K3-level ambulators participated. Standing balance and gait analyses at three self-selected speeds were performed at three different levels of ankle dorsiflexion stiffness (Soft, Medium, and Firm) using the College Park Venture foot (College Park Industries, Warren, MI, USA). Repeated-measures analyses of variance (ANOVAs) were performed on relevant standing balance, gait spatiotemporal, and roll-over shape (ROS) outcomes. Gait kinetic and kinematic data were analyzed using a one-dimension statistical parametric analysis. Results Ankle dorsiflexion stiffness influenced balance and gait. Overall, the Firm dorsiflexion stiffness provided a smaller body sway on standing balance, a ROS radius close to the one of able-bodied individuals, and reduced step length asymmetry while walking. Furthermore, walking speed had an influence on ROS radii, resulting in a larger radius for slow walking speeds and a smaller one for fast walking speeds. Discussion The Firm stiffness appeared to offer the most advantages for balance and gait. The radius of ROS under the Firm condition, close to the radius of able-bodied individuals, could have caused the improvement in step length symmetry by a greater progression of the center of pressure, resulting in further progression of the prosthetic side. This information, in addition to the observed walking speed effect on ROS radii, encourages us to develop studies to examine the effect of walking speed on foot performance and improve prosthetic foot design to maintain the same gait characteristics under different walking speeds. Clinical Relevance These results improve our understanding of how a specific prosthetic ankle dorsiflexion stiffness affects standing balance and gait, which supports the prosthetist's evaluation process to determine specific individual stiffness for each prosthesis user.