Trimline Severity Significantly Affects Rotational Stiffness of Ankle-Foot Orthosis

Abstract

In Brief Ankle-foot orthoses (AFOs) are prescribed to patients suffering from lower limb disorders. Usually made of polypropylene, these braces have the ability to be custom cut and formed to meet the patient's needs, based on how much support they need in certain planes of ankle motion. A study was conducted using a previously designed AFO testing apparatus to test the stiffness of a set of AFOs along the three planes of ankle motion. Three different trimlines (conservative, moderate, and aggressive) were applied to these samples, and data were collected. Data were analyzed using a one-way analysis of variance with Tukey comparison. It was found that all nine groups of data (grouped with respect to plane of motion and trimline depth) yielded significantly different stiffness measures, except for the moderate and aggressive cuts along the abduction/adduction plane. A reproducibility study was also performed, and the range of standard deviations for stiffness measures collected along each axis was found to be 0.068 to 0.460 Nm/°, showing that the testing apparatus can be used by a variety of users and with different specimens with limited variability. In addition, a linear model was fit to trimline length versus average stiffness measure along each plane. These results will serve to further develop a mathematical model to aid in assisting physicians in recommending a proper trimline for a patient, requiring specific stiffness measures along different axes of motion. Ankle foot orthoses (AFOs) are tailored to fit individual patient needs, and can range from stiff and rigid to flexible and articulated, but are rarely quantified for functional measures of mechanical stiffness or range of motion. This study reveals that there is a statistically significant change between the conservative, moderate and aggressive trimlines in stiffness performance. The realization that each trimline produces a significantly different stiffness is vital to the applicability of AFOs to different situations. Information gathered in this study may contribute to the future development of a system for clinicians to determine the appropriate trimline for the patient before fabricating the AFO, thus helping to save time and money.