Dynamic Compliance Characterization of a Prosthetic-Inspired Nonlinear-Stiffness Walking Cane Under Gait-Representative Loading

Walking canes can reduce knee loading in knee osteoarthritis by supporting a portion of body weight. Canes with load-dependent stiffness could modulate this load across stance, but no benchtop method characterizes such behavior. Cane standards (ISO 11334) test static strength, while prosthetic standards define body-mass-based load levels (ISO 10328) and gait-representative motion (ISO 22675). We combined the load levels of ISO 10328 and the motion of ISO 22675 into a benchmarking procedure for load-dependent canes. We recorded reaction force and marker-tracked deformation on a custom motor-driven platform. A commercial carbon-fiber C-shaped prosthetic blade with known nonlinear stiffness served as the reference specimen in two outsole orientations. When mapped to stance phase, the reverse orientation reduced force and the operational stiffness at heel strike and toe-off compared to forward orientation. While not designed as a cane, the blade demonstrates that nonlinear-stiffness elements can modulate the force response across stance. This mapping is approximate and requires human-subject validation. The operational stiffness under continuous motion differed in magnitude and profile from prior static stiffness measurements. A reduced-order formulation, assuming small rotation about the preloaded configuration, reproduced the measured operational stiffness to 6.6% RMSE with one identified coefficient. This parameter-identification method provides a framework for characterizing and designing nonlinear mechanisms in walking aids.