A Distraction Knee-Brace and a Robotic Testbed for Tibiofemoral Load Reduction During Squatting

Abstract

We design and evaluate a new knee distraction unloader brace. The proposed device conforms to the nonlinear behavior of the tibiofemoral contact force during squat motions, by means of patient-custom cams. Using pneumatic cylinders as springs, the unloading assistance provided by the brace is tailored to the patient’s pathology and adjusted during the rehabilitation process. To assess the performance of our orthosis, various tests are conducted to evaluate its efficiency in terms of tibiofemoral contact load reduction. For this purpose, a robotic test-bench, equipped with a robotic arm, emulates upper leg motion under applied forces (hybrid force-motion control). A pseudo-leg is attached to the robot end-effector, and the orthosis is mounted onto it. The test bench is instrumented with two six degrees of freedom force-torque sensors. Using these force sensors as ground truth, tibiofemoral contact force measurements are obtained with and without our orthosis and compared. A pair of cams is fabricated based on data from a patient whose information is retrieved from the Orthoload database. Experimental results demonstrate a contact force reduction of up to 100% within the force range corresponding to the robot’s maximum capacity.