Loads on the uprights of a knee-ankle-foot orthosis

Background: Objective design criteria for orthotic components is lacking. This paucity of data results in prescription guidelines based on assumptions or practitioners' past experience, and the potential for incorrectly designed components. The purpose of this study was to directly measure loads on the knee joint of a knee-ankle-foot orthosis. Study design: Case series. Case Description and Methods: Three subjects who had been prescribed a knee-ankle-foot orthosis for quadriceps weakness underwent gait analysis and orthotic upright load data collection. A load sensor to measure the three force and three moment components was used in place of the lateral knee joint while the subjects walked in three knee flexion positions. Findings and Outcomes: Forces were highest in compression and moments were greatest in the sagittal plane. The kinetics did not increase solely with patient weight. There was substantial variability between subjects. Conclusions: This data will help guide orthotic component design and prescription guidelines. Knowledge of loading conditions will lead to more optimal orthotic intervention for patients and increased patient satisfaction. Clinical relevance: This study is one of the first to directly measure loads on the upright of a KAFO. These data provide objective targets for engineering design. The data from this small case series can also be used to establish guidelines for patient device selection.