Ankle Foot Orthoses (AFOs) are devices engineered to assist a person with a motor impairment. This study sought to create an optimized approach to ankle-foot orthoses design that would provide the best medical functionality, comfort, and ease of use while also being affordable. To the authors’ knowledge, there are no similar approaches in the industry. The protocol begins by creating a 2-dimensional “unfolded” model of an AFO, where the AFO is modeled as a 3-dimensional surface in a 2-dimensional sketch. Then, laser-cutter technology is used to cut a thermoplastic resin sheet into the desired 2-dimensional shape. After, the final 3-dimensional product is then produced by bending along proper creasing lines. This method is ideal because it lowers manufacturing difficulty, time, and cost, while also producing an optimal solution to a great functional need.

Cerebral Palsy (CP) is a non-progressive disorder that affects cognitive and functional abilities. It often leads to diminished gait performance, which, in its most extreme case, can completely impair one's ability to walk.

One common observation in CP patients is drop foot- a condition in which the foot does not properly rotate during the swing phase of walking. A person with drop foot cannot lift their entire foot when walking, resulting in little to no clearance between the toes and the ground, causing the toes to drag and inhibiting any regular motion.

One solution is providing proper foot support in the form of an Ankle Foot Orthoses (AFO). An AFO is used to restore walking ability by either keeping the peripheral joints in a range of motion that will reduce pathological reflex patterns or restricting motion the user would naturally perform incorrectly.  For example, the talus of the ankle is held to eliminate downward rotation caused by drop foot.  In terms of general walking improvement, an AFO specifically helps to improve gait kinematics, decrease user energy, and facilitate the development of motor skills. Gait parameters improved are the range of motion of both the ankle and knee joints, as well as increased walking ease, speed, and stride length.

There are a variety of AFO designs on the market, including the solid AFO (SAFO), dynamic AFO (DAFO), floor reaction orthosis (FRO), posterior leaf spring (PLS) and the hinged AFO (HAFO).  AFO's also have varying mechanical complexity ranging between passive, semi-active, and active devices.  A passive AFO can store and release energy elastically and functions by physically holding the ankle complex around the correct position. Semi-active AFOs have some sensor function, and active devices incorporate active movement of the joint (i.e. exoskeleton).

AFO design optimization seeks maximum comfort, high resistance to mechanical failure, and sufficient support. One of the best ways to analyze the mechanical properties of a complex flexible mechanism is the process of finite element analysis (FEA). In this study, an educational version of the software Fusion 360 (version 2.0.6670), was utilized to conduct an effective analysis used for design optimization.

There are several materials commonly used for AFO design. Some are sturdy and provide ankle-joint stability, but split or crack along pressure points with repeated use. Others are flexible and provide comfort while sacrificing ankle-joint stability. This study compared several thermoplastic materials for stress tolerance and deformation resistance.

Although orthoses have been improved over time to address a user’s physical needs, manufacturing and financial restrictions are still an obstacle. This study sought to create an orthosis that achieved these improvements by using a novel design approach. This would allow more people to have a comfortable, functional solution to their gait abnormalities without suffering unreasonable financial burden.


Stiffness Analysis of a Simplified Ankle-Foot Orthosis

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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