An Experimental Cadaveric Limb Motion Platform for Detecting Altered Mechanical Responses under Small-Joint Defect Conditions

This proof-of-concept study developed a novel in vitro biomechanical evaluation platform for quantitatively detecting altered mechanical responses in small joints under controlled structural perturbations. The platform was designed to apply repeatable flexion-extension cycles to ex vivo rabbit hindlimb specimens while enabling synchronized measurement of global reaction force and localized periarticular deformation. Four specimens were tested under baseline and post-perturbation conditions, with controlled bone resections of increasing magnitude introduced following standard surgical procedures and quantified using the Relative Incision Length (RIL). To characterize perturbation-induced mechanical changes, two dimensionless indices were defined: the Relative Amplitude Difference (RAD) to represent changes in global dynamic force response and the Strain Alteration Index (SAI) to quantify changes in marker-derived apparent in-plane strain. Force attenuation was observed in all four specimens under both the 0-35° and 0-70° motion profiles. Under the 0-35° profile, RAD showed progressively greater attenuation with increasing RIL, ranging from -32% to -93%, whereas the ordering was less uniform under the 0-70° profile. The strain-based response also varied with motion range and strain metric. The smallest perturbation exhibited among the largest relative strain increases under both profiles, while the intermediate and larger perturbations did not show a uniform graded ordering. These findings indicate that global force and regional apparent in-plane strain provide complementary, motion-dependent quantitative readouts of mechanically altered joint behavior rather than a single angle-independent relationship with perturbation magnitude. Overall, the proposed platform establishes an accessible and controllable in vitro biomechanical framework for comparing mechanical responses across controlled structural and motion conditions and provides a foundation for future evaluation of artificial finger joint designs under conditions such as implant undersizing, geometric mismatch, or altered joint congruence.