Dimensional accuracy of ankle-foot orthoses constructed by rapid customization and manufacturing framework

Abstract

Passive-dynamic ankle-foot orthoses (PD-AFOs) constitute a class of ankle braces that rely on material properties and physical features to establish functional characteristics such as bending or rotational stiffness. We have developed a novel framework that combines a fully parameterized PD-AFO computer-aided design (CAD) model and free-form fabrication to rapidly manufacture customized PD-AFOs. The three-dimensional locations of select anatomic landmarks serve to fit customize the PD-AFO CAD model. A virtual orthopedic alignment process and selection of discrete design parameter values further customize the orthosis, which is fabricated via selective laser sintering. CAD models were customized and full-scale orthoses were manufactured for two nondisabled subjects. The surface of one half-scale CAD model was marked with 3 mm hemispherical dimples, and four orthoses were manufactured in different build orientations and positions. Dimensional accuracy was determined by calculating discrepancies between corresponding CAD and fabricated orthoses interdimple distances. Subjective evaluations of the full-scale PD-AFOs following use in gait were positive. Dimension discrepancies were well under a 2 mm tolerance for the four half-scale orthoses. Mean foot plate, strut, and cuff component discrepancies were 0.31 +/- 0.28, 0.34 +/- 0.08, 0.52 +/- 0.39 mm, respectively, and 0.29 +/- 0.23 mm for the overall orthosis. Dimensional accuracy of the rapid customization and manufacturing framework was well within tolerances suggested in the literature.