Experimental Investigation: Strain Measurement on a Polypropylene Ankle-Foot Orthosis During Normal Gait

Advances in medicine and science across the nation have succeeded in improving survivorship after traumatic injuries and illness, making patient’s quality of life and functional mobility independence even more important. Ankle-Foot Orthosis (AFO) is prescribed to patient who suffered a stroke (Fig. 1). Stroke causes abnormal motions at the ankle-foot joints referred as Drop-Foot (DF). The DF is defined as a toe drag instead of the heel contact during gait. This toe drag lead to an increase of stresses in soft tissue, and ulceration in the forefoot. The AFO can alleviates the DF by constrain excessive plantar flexion. In the current clinical application, the AFO is made of a thermoplastic material called Polypropylene (PP). It is custom fabricated and fitted to the patient. In order to minimize failure and attempt to predict their fatigue life, experimental determination of the strain response is needed. However, the PP is an inert plastic. Its low surface energy characteristic makes difficult to adhere wire strain gages (Briggs, 1982). Therefore, the objectives of the study are (1) developing a method to enable reliable bonding between conventional strain gages and a PP AFO, and (2) developing an instrumentation which will simultaneously record strains information at specified locations (Fig. 1). More important, these strain information can be used to validate data obtained earlier using Finite Element Method (Chu, 1992).