Characterizing 3D Force Vectors to Improve the Assessment of Spasticity

Hyperactive tendon stretch reflexes are a part of the definition of spasticity in chronic stroke survivors. Generally, to assess spasticity, the Modified Ashworth Test is performed, which indirectly quantifies the stretch reflex threshold via a ‘catch’ angle. To precisely quantify the stretch reflex threshold for any individual, previously we established an instrumented tendon indentation method that utilizes a tendon tapper connected to a controller with position feedback, with a load cell attached to the tapper end. Our ultimate goal is to develop a portable version of our device to be used in clinical settings for more accurate and precise quantification of spasticity. One of the limitations of this method for general or clinical use was that it utilized a load cell which provided information in a single dimension, orthogonal to the long axis of the biceps tendon. To assess whether the tapper is located on the tendon in a consistent position during the quantification process, continuous monitoring of the load cell signal and patient movement is necessary. Accordingly, in this study, we propose a novel approach that overcomes the above-mentioned limitations by utilizing analytical techniques to characterize the three-dimensional force vector of an attached multi-dimensional load cell. This approach allows for an online assessment of the positioning of the tendon tapper, as well as the potential to identify a more robust 3-D reflex force threshold.