Evaluation of the Structural Integrity and Functionality of a Stance Control Knee Ankle Foot Orthosis Knee Joint Using Experimental and Computational Approaches

Abstract

Walking is an essential part of daily mobility, but individuals with conditions such as polio, muscle weakness, spinal cord injuries, or multiple sclerosis often depend on Knee-Ankle-Foot Orthoses (KAFO) that keep the knee locked throughout both the stance and swing phases of walking. This restriction leads to abnormal gait patterns, increased joint stress on the hip and lower back, and a reduction in gait efficiency. To overcome these drawbacks, Stance-Control-Knee-Ankle -Foot-Orthosis (SCKAFO) has been developed, offering knee support during the stance phase and permitting knee movement during the swing phase. This study presents a combined in silico and experimental analysis of a mechanical SCKAFO using a commercially available predicate device. Experiments were conducted to evaluate the unlocking forces of the knee joint. To replicate the rigid body dynamics behaviour of the orthosis, a simplified 3D CAD model was created, and the results of rigid body dynamics match the experimental findings. Also, the structural response of the orthosis knee joint under both theoretical and actual loading scenarios was examined using finite element analysis. In silico results shows that the orthosis knee joint is structurally safe under the worst loading condition.  The validated simplified 3D CAD model demonstrated close agreement with experimental results, showing deviations of 3.96 % at the pawl cable and 2.61 % at the foot loading. It revealed equivalent von Mises stresses of 8.63 MPa under theoretical loading and 4.70 MPa under practical loading, underscoring the potential of analysis-driven design to advance next-generation mechanical SCKAFO knee joint development, despite minor variations from cable dynamics and model simplifications.