A novel method to analyze the mechanics of unloader braces for medial knee osteoarthritis

Marcus Brown Department of Mechanical and Materials Engineering, Queen’s University, Kingston, Canada Background Bracing is a treatment option for medial knee osteoarthritis [1] that unloads the medial knee through the application of an external moment (brace moment) [2]. In theory, the brace moment is designed to reduce the total external adduction moment, as disease severity and external adduction moment are correlated [3]. The braces used in this study operate according to the principle of three-point bending [2] (Figure 1). A load is applied to the lateral knee (Figure 1, FK), and two reaction forces are applied to the thigh and shank (Figure 1, FT and FS), generating the brace moment at the knee (Figure 1). According to this loading, brace moment is affected by the magnitude of the lateral load, and the distance from the lateral load to the thigh and shank reaction forces (Figure 1, dT and dS), called the thigh and shank lever arms. The magnitude of the lateral load can be controlled using adjustment screws, however the brace lever arms are defined by brace fit and design. Previous studies have quantified the brace moment using direct measurements [2] or using approximations [1,4], however no studies have considered the pressure distributions applied by the brace to the user. These are important as they can be used to better estimate the lever arm distances, and quantify the effect of design elements on brace moment. Therefore, the purpose of this study is to provide a novel means of analyzing brace mechanics, specifically by measuring the pressure distributions and lateral force applied at the knee between the brace and the user. Included in this objective is the comparison of two braces, to establish whether the proposed method is suitable to identify differences in the functionality of different brace designs.