Development of a Robotic Unloader Brace for Investigation of Conservative Treatment of Medial Knee Osteoarthritis

Abstract

Knee osteoarthritis (KOA) is a painful and debilitating condition that is associated with mechanical loading of the knee joint. Numerous conservative treatment strategies have been developed to decrease pain, improve mobility, and delay time to total joint replacement. Unloader braces are commonly prescribed for medial uni-compartmental KOA, however their evidence of efficacy is inconclusive and limited by user compliance. Typical commercial braces transfer load from the medial compartment to the lateral knee compartment by applying a continuous brace abduction moment (BAM). We propose that brace utilization and effectiveness could be improved with a robotic device that intelligently modulates BAM in real time over the course of a step, day, and year to better protect the knee joint, improve pain relief, and increase comfort. To this end, we developed a robotic unloader knee brace ABLE (active brace for laboratory exploration) to flexibly emulate and explore different active and passive brace behaviors that may be more efficacious than traditional braces. The system is capable of modulating BAM within each step per researcher defined unloading profiles. ABLE was realized as a lightweight orthosis driven by an off-board system containing a servo motor, drive, and real-time controller. Frequency response and intra-step trajectory tracking during level-ground walking were evaluated in a single healthy human subject test to verify system performance. The system tracked trajectories with a root mean square error of 0.18 to 0.58 Nm for conditions varying in walking speed, 85-115% nominal, and trajectory peak BAM, 2.7 to 8.1 Nm. Biomechanical and subjective outcomes will be evaluated next for KOA patients to investigate how novel robotic brace operation affects pain relief, comfort, and KOA progression.