Foot drop is a neuromuscular disorder characterized by steppage in the gait cycle that makes the patient unable to perform dorsiflexion or lift the forefoot. This condition is commonly found in patients with stroke or cerebral palsy. For rehabilitation, Ankle-Foot Orthosis (AFO) is used to treat foot drops. The fabrication process of Ankle-Foot Orthosis is usually performed for a specific case and customized for a single person. Trial and error in the fabrication process are chosen to obtain the correct design. A simulation could be performed to analyze the failure condition of AFO to mitigate this condition, especially in fracture conditions during the gait cycle. Therefore, computational analysis is needed to save more time and cost in the AFO design. This study aims to observe the Ankle-Foot Orthosis model simulation for foot drop cases in the stance phase. The model was developed and analyzed using Solidworks. This study focuses on the GRF on initial contact, mid-stance, and terminal stance in the stance phase. On the other hand, the minimum stress was located on the tip of footplate or the top part of superior-inferior of the AFO. Minimum deformation was also found at the superior-inferior of the AFO since it is the fixed support location. Minimum strain could be found at the tip of the footplate.
The loads applied in the footplate led to stress concentration in the ankle trimline because the center of rotation is around the ankle (aligned with the fixed constraint). During the initial contact, the contact area is the smallest among the other sub phases. Thus, the von Mises stress during initial contact was the highest. The role of material type is also significant in this simulation. Polypropylene is the standard material used for AFO due to its thermoplastic character.
Based on the simulation result, the proposed model of AFO showed the highest stress in the AFO when it was in the initial contact sub-phase. That was the first contact between the foot and the floor covered by the heel’s small area. This value was still lower than the model’s material’s elastic modulus, which indicated that the result was safe. However, the presence of the concentrated stress would likely be the location of the crack after the AFO is used for an extended amount of time. The AFO was quite stiff because of this material, and this property was beneficial since the AFO keeps the foot in a dorsiflexion position and prevents plantar flexion. This condition also initiated the beginning of the gait cycle, which is the heel’s initial contact. The most considerable deformation also happened in the initial contact phase. The AFO deformed mainly in the initial contact position since the most significant stress was concentrated in this step. The tip of the AFO deforms from its initial position when force is applied. This deformation was still normal since this condition only stays for 10% of the stance phase.
In the foot drop case, the use of AFO aimed to have more foot clearance, especially in the terminal stance, since the patient could do the foot’s dorsiflexion. The maximum stress found in the AFO during terminal stance indicated that the AFO could withstand the GRF from the user and give foot clearance right after the terminal stance. The deformation and strain of AFO during the terminal phase were also the lowest among the other two sub-phases in the stance phase. This AFO design could be used in the foot drop case with the same type of material as the simulation. This study’s future challenge is to perform the experimental setup to test the design with the user’s proposed material, and his gait will be analyzed. This study focuses only on one loading for one patient-specific AFO. The model only showed the mechanical behavior during static analysis, but the devices’ response during fatigue is not modelled. The straps used to fix the patient leg on the AFO could have been modelled for future study. The presence of straps could increase the model’s complexity since there is contact between the strap and the AFO. For further study, the boundary condition should be set similar to the loading during gait. For further study, the boundary condition should be set similar to the loading during gait.
Author: Alfian Pramudita Putra, S.T., M.Sc.
The result of study has published on Journal of Engineering, Science, and Technology (April 2022). To read the article, click this link below:
https://jestec.taylors.edu.my/Vol%2017%20Issue%202%20April%20%202022/17_2_12.pdf
Putra, A. P., Rahmatillah, A., Rodhiyah, N. K., Pujiyanto, & Pawana, I. P. A. (2022). COMPUTATIONAL ANALYSIS OF ANKLE-FOOT ORTHOSIS FOR FOOT DROP CASE DURING STANCE PHASE IN GAIT CYCLE. Journal of Engineering Science and Technology, 17(2), 885-996.
