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

Abstract

Bracing is a treatment option for medial knee osteoarthritis that reduces compressive forces in the medial knee through the application of an external brace moment. In theory, this moment reduces the external knee adduction moment, whose magnitude has been related to the severity of osteoarthritis (Miyazaki et al., 2002). Studies have quantified the brace moment to determine whether it could significantly reduce joint loads (Pollo et al., 2002; Self et al., 2000; Schmalz et al., 2010), however none have considered the pressure distributions between the brace and the user, which can be used to evaluate the impact of specific design components on the brace moment. Therefore, the purpose of this study was to provide a novel method of analyzing brace mechanics using pressure measurements between the brace and the user. The experimental setup consisted of a motion capture system, an instrumented treadmill, two pressure mats, and two load cells. This setup was used to quantify important aspects of brace mechanics, specifically, the thigh lever arm, the force applied to the lateral knee, the brace deflection, the brace moment, and the brace stiffness. Two braces were tested, being a single-hinged brace and a dual-hinged brace, on five subjects, who performed two thirty second walking trials on the instrumented treadmill. The results showed that there was some variability as a percentage of stance phase, however, brace mechanics were consistent through mid-stance. Therefore the braces were compared at mid-stance using a paired t-test. This showed a larger lateral load (p < 0.01), brace deflection (p = 0.02) and brace moment (p < 0.01) for the dual-hinged brace, while the stiffness of the single-hinged brace was larger (p = 0.03). Furthermore, there were no observed differences in the thigh lever arm between the braces (p > 0.05). These differences were attributed to design features of the braces, the most important being the tightening mechanism, which we believe contributed to both the higher lateral load and the lower stiffness for the dual-hinged brace. Using these results and the pressure distributions, a new brace design was proposed, modifying brace features to increase brace effectiveness. Overall, the proposed method proved useful when comparing braces, and allowed for brace improvement, making it a reasonable non-invasive means of analyzing brace mechanics.