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Background: Articulated or hinged ankle-foot orthosis (AFO) allow more range of motion. However, quantitative investigation on articulated AFO is still sparse. Objective: The objective of the study was to quantitatively investigate effects of alignment and joint types on mechanical properties of the thermoplastic articulated AFO. Study design: Tamarack dorsiflexion assist flexure joints with three durometers (75, 85 and 95) and free motion joint were tested. The AFO joint was aligned with the center of the motor shaft (surrogate ankle joint), 10 mm superior, inferior, anterior and posterior with respect to the motor shaft center. Methods: The AFO was passively moved from 20 plantar flexion to 15 dorsiflexion at a speed of 10 /s using a motorized device. Mechanical properties including index of hysteresis, passive resistance torque and quasi-static stiffness (at neutral, 5, 10 and 15 in plantar flexion) were quantified. Results: Significant effects of joint types and joint alignment on the mechanical properties of an articulated thermoplastic AFO were revealed. Specifically, center alignment showed minimum resistance and stiffness while anterior and posterior alignment showed significantly higher resistance and stiffness. The dorsiflexion assist torques at neutral position ranged from 0.69 AE 0.09 to 1.88 AE 0.10 Nm. Conclusions: Anterior and posterior alignment should be avoided as much as possible. Clinical relevanceThe current study suggested that anterior and posterior alignment be avoided as much as possible in clinical practice due to potential skin irritation and increase in stress around the ankle joint.

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The pathophysiologic process that results in bone erosion from frontal sinus mucoceles has long been a mystery. Traditionally, bone erosion has been attributed to pressure. However, no scientific evidence has yet been presented to support this hypothesis. To answer this question, seven cats had a mucocele created in one frontal sinus, with the other sinus left as a control. A manometer was inserted into each frontal sinus. Pressure readings were taken over a 7-month period. Pressures on the mucocele side were higher than on the control side and were sufficient to erode bone. Bone was thicker on the mucocele side than on the control side. This study established that mucoceles exert sufficient pressure to erode bone, and that such erosion may be part of a two-stage process.