Effects of trimline cut in ankle foot orthosis: An experimental and finite element analysis

An Ankle-foot orthosis (AFO) is a structure that spans from the lower leg to the foot and controls ankle joint movement. It prevents or assists the human body's lower leg and foot in replicating a normal human gait. The purpose of AFO is to achieve a stable gait by controlling the musculoskeletal system adequately. The mechanical features of AFO stiffness will play an essential role in helping gait, if this stiffness is not matching to the patient's conditions, gait will decrease and knee joint motion will be compromised. In general, trimline cut were introduced in the AFO medial and lateral side to control the stiffness of orthosis. However, this will result in stress concentration in the ankle region and lead to failure of AFO. In this study first evaluate the effects of trimline cut in AFOs using finite element analysis with three geometrical shapes like circle, elliptical and slot were introduced on the dorsal side. The stress concentration and stiffness of AFOs in the ankle region were computed. The stiffness of the basic model and trimline cut AFO model were compared and found elliptical trimline cut model is optimum one. The experimental analysis was performed using 3D Printed AFOs and calculated stiffness. It was observed that finite element analysis results, stress concentration of trimline cut models were reduced maximum of 2 % with basic model (without trimline cut)., whereas, in the experimental study of 3D-Printed AFO of trimline cut model, stiffness were reduced around 16 % compared with basic models. This study clearly indicates that, geometrical shapes trimline cut influencing on stiffness of AFOs. It will give the insight's for orthosis designers to make custom design of AFOs in particularly foot drop conditions to optimized the stiffness of orthosis.