Quantifying Passive Biomechanical Stability Using an Industrial Robot: Development and Experimental Validation of a Task Space Motion Framework

This paper presents a methodology and generalized motion framework for quantifying passive biomechanical stability and Range of Motion of human cadaveric specimens, using a position-controlled industrial robot and a wrist-mounted force/torque sensor. Many biomechanical studies on diarthrodial joints using human cadaveric specimens are published in the literature, using various test protocols and machines to apply the loading conditions. In these studies, laxity or mobility of the joints are quantified by measuring the magnitude of translations and rotations with respect to force and torque. The protocols and anatomical motions of the specimens are usually described high-level, textually, and from a medical perspective to a broad audience. The present paper aims to describe, from a technical perspective to a robotics audience, our method to perform biomechanical studies and how existing protocols can be replicated through parameterization using the existing textual descriptions. To accomplish this, we propose a generalized task space motion framework for performing biomechanical studies on diarthrodial joints. The generalization is made by defining the robot Tool Center Point at the cadaveric joint rotation center and aligning the specimen so the anatomical motions can be modeled in world frame or tool frame. The framework was successfully evaluated in a technical pilot study on the shoulder, using one cadaveric shoulder specimen and an established protocol from the literature. The specimen was tested in the intact state and in an injury state, with increased passive instability observed for the injury state compared to intact state.