Development and experimental characterization of a cadaveric stance simulator for residual limb biomechanics

Understanding the biomechanical interaction between residual limbs and prosthetic sockets is essential for optimizing prosthesis design and minimizing tissue injury. Existing cadaveric stance simulators have not been specifically designed to examine socket-residual limb biomechanics. This study designed, constructed, and evaluated a cadaveric stance simulator capable of applying physiologically representative compressive forces through residual limbs. The long-term objective is to utilize dynamic stereo x-ray (DSX) to quantify 3D skin strain at the socket-residual limb interface, for which this simulator serves as a critical foundational step. The simulator combined passive spring compression with active stepper motor control to generate characteristic double-peaked vertical ground reaction force (vGRF) profiles of stance phase. Primary validation was performed under idealized conditions using a rigid prosthesis configuration, with cadaveric testing as a secondary feasibility assessment on two residual limbs with direct force plate measurement. Validation metrics included peak vGRF, peak-to-valley (P2V) ratio, first-to-second peak symmetry (P2P), and loading and unloading rates, with target parameters derived from five participants with transtibial limb loss. Non-parametric analyses compared simulator outputs with control data. Spring-based force estimates were validated against force plate measurements using root mean square (RMS) error and Bland-Altman analyses. Idealized trials showed no significant differences across validation metrics, indicating the simulator closely matched selected physiological loading metrics. Exploratory cadaveric comparisons demonstrated lower peak vGRF, P2V ratio, and unloading rates relative to control participants, attributable to intentional force reductions to preserve tissue integrity. Spring-based force estimates demonstrated preliminary agreement with force plate measurements, supported by RMS error and Bland-Altman analysis. The stance simulator provided a repeatable, adaptable platform for physiologically representative residual limb loading. Its compatibility with DSX imaging establishes a foundation for quantifying 3D skin strain at the socket-residual limb interface, supporting improved socket design and outcomes for individuals with lower limb loss.