Multi-joint rigidity-testing device for titrating medication and deep brain stimulation therapies

Abstract

Disabling motor signs of Parkinson's Disease including akinesia, bradykinesia, tremor, and muscle rigidity are typically quantified by clinicians using the Unified Parkinson's Disease Rating Scale (UPDRS). These subjective assessments, while useful, often vary among clinicians, making it challenging to evaluate medication and deep brain stimulation (DBS) therapies in multi-center trials. In this study, two designs for a multi-joint rigidity-testing device were developed to enable objective, quantitative measures of rigidity. The investigator passively manipulated the subject's joints while stabilizing the appendage distal to the joint with two opposing force transducers, providing a measurement of differential force during the movement. These forces were synchronized to the joint angle, measured by a motion capture camera system. Here, we show feasibility data for detecting changes in muscle rigidity in a parkinsonian non-human primate treated with Sinemet, Globus Pallidus internal (GPi) DBS and/or subthalamic nucleus (STN) DBS. For design 1, the device was tested on six joints: elbow, wrist, shoulder, hip, knee and ankle, and in three states: MPTP, DBS stimulation, and drug therapy. Device 1 was effectively able to quantify rigidity and determine changes in rigidity states among all joints except elbow (p<0.05). For design 2, the device was tested on only the shoulder abduction/adduction and was tested in three states: MPTP, DBS stimulation, and post-DBS stimulation. Design 2 was effectively able to quantify changes in rigidity as well (p<0.05). Ergonomics and durability were considered in the evaluation of the devices. While each device showed promising results, future iterations will also need to address several limitations of the current devices. The eventual goal of this rigidity testing device would be to use it in the clinic to assist neurologists in titrating medication levels and DBS parameters.