Characterizing the interaction effects of modular components on transtibial prosthesis stance-phase mechanical behavior.

Background: Despite evidence that passive prosthesis mechanical properties can directly affect user experience, prosthetists have access to minimal information regarding the mechanical interactions between a prosthetic foot and proximal modular componentry.

Objectives: This study quantified the stance phase mechanical behavior of a transtibial prosthetic system through the addition of passive modular componentry to a dynamic response (DR) foot.Study Design:Repeated measures, mechanical characterization.

Methods: Maximum displacement and energy return were measured with a materials test machine simulating initial, mid, and terminal stances. Twelve conditions were tested: a DR foot in combination with a hydraulic ankle at 2 resistance settings and 3 different shock-absorbing pylons (SAPs). The roll-over shape of the DR foot with and without hydraulic ankle was measured using a test rig.

Results: Adding modular passive components altered displacement and energy return, displaying independent and interaction effects. Generally, the hydraulic ankle and SAP reduced energy return (up to 18%) but decreased (up to 51%) and increased (up to 88%) displacement, respectively, while the combined properties were more complex. Roll-over shape radii decreased with increasing load for the foot alone but exhibited a nonlinear response with the addition of the ankle.

Conclusions: Inclusion of modular components in a transtibial prosthetic system can have complex mechanical interactions that independently affect the system's response to load. It is important for clinicians to be aware of the cumulative effects of these interactions to inform the tuning of transtibial prosthesis mechanical behavior. Combinations of hydraulic ankles and SAPs can help clinicians adjust the prosthesis to achieve a balance between user comfort and energy return.