Three-spring flexion-resistance module for knee orthoses design and evaluation

ObjectiveKnee orthoses assist patients with joint instability, yet many passive designs provide limited energy dissipation and flexion-load regulation during high-demand activities. This study designed and validated a compact three-spring shock-absorption mechanism to provide quasi-passive flexion resistance, improve energy absorption, and redistribute loads in knee orthoses.MethodsA mechanical design and validation study was conducted combining analytical modeling, finite-element simulation, and pilot functional testing. The mechanism integrates two compression springs and one tension spring housed in an aluminum frame. Finite-element simulations (ANSYS Explicit Dynamics^®) evaluated deformation, absorbed energy, and von Mises stress under dynamic loading over a 0-70° motion range, and were calibrated using experimental compression/tension tests of single and paired springs. Three functional prototypes were fabricated and evaluated by three adult volunteers using one-leg rise and deep-squat tasks, with perceived assistance recorded on a 100-mm Visual Analogue Scale (VAS) under institutional ethics approval.ResultsSimulated and experimental endpoint force and total deformation (L₀ - Lf) showed close agreement, with relative deviations below 3%. For the evaluated configuration, the orthosis generated an estimated total passive flexion resistance of 70.54 Nm for two modules, corresponding to a case-specific 48.22% reduction in required flexion torque when referenced to a representative post-ACLR peak torque (146.30 Nm). Peak stresses remained below the yield strength of 6061-T6 aluminum, while the beam-base interface was identified as the durability-critical region. Functional testing yielded mean VAS scores of 36.67 ± 2.89 (one-leg rise) and 41.67 ± 5.77 (deep squat), indicating moderate perceived assistance.ConclusionsThe proposed multi-spring mechanism provides measurable quasi-passive resistance and withstands conservative high-flexion loading, supporting its feasibility as a compact assistive concept. These proof-of-concept results motivate further work on fatigue/wear assessment, multi-objective optimization, and larger clinical studies with objective functional outcomes.