Design and mechanical testing of Afo to control foot drop among patients with peroneal nerve injury

Abstract

Ankle- Foot Orthotics (AFO) is an assistive device to support and correct the abnormal gait pattern due to peroneal nerve injury. The stiffness of the AFO posterior leaf spring (PLS) area is the key factor that influenced the patient's gait-related problem. Currently it was difficult to achieve the optimal stiffness at the PLS area after thermoforming with the currently used standard flexible AFO. Therefore, the patient needed to repeat the clinic visit for fitting adjustment. The purpose of this research study was to design and fabricate an adjustable Posterior Leaf Spring (PLS) AFO and to perform static and dynamic mechanical tests between the PLS AFO and flexible AFO. The PLS strut of the PLS AFO was made with 8mm thickness of Polypropylene (PP). However, for flexible AFO, the PLS area was made with a double layer of 3mm PP and 5mm PP by vacuum thermoforming. Mechanical testing was performed using an Instron 8801 machine between the two AFO designs. The stiffness value of the PLS AFO was 0.94 Nm/ ∘ , and flexible AFO was 0.83 Nm/ ∘ during the static loading test. Energy dissipated ratios (hysteresis index) were 34.32% and 36.12% with PLS AFO, while 42.7% and 45.28% with flexible AFO, during plantarflexion and dorsiflexion, respectively. After 110,000 cycles of fatigue testing, the distal rivet of the PLS AFO became loose, although the flexible AFO had no problem. In conclusion, the novel adjustable PLS AFO achieved non-inferior mechanical properties such as lower energy dissipated ratio and was easier to determine the stiffness value for the particular patient than the flexible AFO except for the fatigue strength. As a preliminary study, this study is fundamental for future studies. IMPLICATION OF THE THESIS: This study will benefit patients with drop foot gait in a resource-limited environment by decreasing the repetitive clinic visits for fitting adjustment and better assisting during the push-off phase. The clinician's benefit was that it was easy to adjust the PLS stiffness with the proper material thickness for the patients with different body weights to meet the biomechanical needs.