RESUMEN
This study investigates if fabrication techniques employed at different orthotic centres affect the characteristics of the manufactured plastic orthoses. Plaster models were formed from the same master mould. The thickness and bending stiffness of the supplied polypropylene sheets were measured prior to fabrication. An orthotic technician at each of the 3 orthotic centres manufactured 4 homopolymer and 4 copolymer polypropylene ankle-foot orthoses (AFOs), following each centre's fabrication practice. Another technician at one of the orthotic centres manufactured an additional 4 homopolymer and 4 copolymer AFOs. The thickness, the dorsiflexion stiffness and plantarflexion stiffness of the 32 fabricated AFOs were monitored and compared. Analysis of the results suggests: Copolymer polypropylene sheets are supplied marginally thicker than homopolymer polypropylene sheets. The difference between the thickness of the 16 copolymer and 16 homopolymer AFOs was not significant. The thickness of the AFOs manufactured in copolymer was less consistent than homopolymer. Dorsiflexion stiffness of the copolymer AFOs was less consistent than homopolymer AFOs. Although the bending stiffness of the copolymer and homopolymer sheets differed significantly, there was no significant difference between the dorsiflexion stiffness of the copolymer and homopolymer AFOs. Plantarflexion stiffness was consistent for both the copolymer and the homopolymer AFOs and there was no significant difference between the plantarflexion stiffness of the copolymer and homopolymer AFOs. The thickness and flexural stiffness of the AFOs manufactured by 2 technicians at the same centre did not differ. These results are useful benchmarks for the flexural stiffness of AFOs.
Asunto(s)
Diseño de Equipo/métodos , Aparatos Ortopédicos , Docilidad , Polipropilenos , Tobillo , Elasticidad , Humanos , Ensayo de MaterialesRESUMEN
This paper compares the bending stiffness of 5 different colours of copolymer polypropylene (CCP) with that of natural copolymer polypropylene (NCP). Flesh coloured and natural sheets are supplied thicker than other pigmented sheet. The bending stiffness of a specimen may be defined as EI, i.e. the product of E, Young's modulus of elasticity and I, the 2nd moment of area. Strips of "as supplied" (AS) and "post-draped" (PD) specimen were clamped and subjected to bending to assess the effect of pigmentation on bending characteristics. The gradient of the graph of bending deflection delta versus bending moment enables EI to be estimated. The process of thermoforming polypropylene reduces EI, the bending stiffness. However, the manual draping and vacuum procedure introduces so many variables that it is difficult to quantify the effect of pigmentation. The E of a bent specimen may be estimated from the gradient of the graph of deltaI versus bending moment. In the case of AS sheet, the effect of pigmentation on E is inconclusive. PD specimens indicate a significant reduction in E due to thermoforming. This was verified by an electron-microscope study of AS and PD specimens. Draping an ankle-foot orthosis (AFO) results in a non-uniform wall thickness. The results of this study with respect to the effects of pigmentation on the bending stiffness of AFOs are inconclusive. More detailed studies require to be completed in order to confirm which factors are responsible for this non-uniformity in wall thickness and consequent variation in bending stiffness.