Design and evaluation of a passive hydraulic simulator for biceps spasticity

This thesis presents the design framework for a passive (unpowered) clinical training simulator using purely mechanical components to help improve the accuracy and reliability of clinical assessment. In the scope of this thesis, a prototype simulator was developed to replicate a common abnormal muscle behavior, biceps spasticity, at different levels of severities. Spasticity is often found in patients with stroke, spinal cord injuries, and other neurological disorders causing abnormal motor activity. The current assessment of spasticity is via in-person evaluation using qualitative clinical scales, and the accuracy and reliability of this method heavily depend on assessors’ previous training and clinical experience. However, the current training methods cannot provide students sufficient amount of practice, resulting in lack of proficiency and missing clear understanding of spasticity behavior. The motivation of this project is to develop a self-contained, unpowered simulator to complement the current clinical assessment training. The design process started by characterizing the main behavioral features of the spasticity and selecting the appropriate mechanical design features that provides haptic feedback comparable to a spastic biceps muscle. The prototype was further validated by a two-stage evaluation process. The first part of evaluation involved examining the performance of individual mechanical design features and their combined performance through bench-top experiments. In the second part of evaluation, clinicians were invited to assess the replicated spasticity behavior and to compare the simulation with their previous experience interacting with actual patients. The bench-top performance and clinical feedback help design iteration and provide insights into the future development of the training simulator. Preliminary results suggested the feasibility of using the simulator as a training tool to teach spasticity assessment in a classroom setting

Quantification of spasticity and rigidity for biceps and triceps using the PVRM (position, velocity, and resistance meter)

Spasticity and rigidity are two common types of abnormal muscle behavior seen among patients with neurological disorders (e.g., stroke, Parkinson’s Disease). Clinical assessment of increased muscle resistance during passive movement, or hypertonicity, involves qualitative and subjective scales such as the Modified Ashworth Scale (MAS) for spasticity or the Unified Parkinson’s Disease Rating Scale (UPDRS) for rigidity. Inaccurate and inconsistent assessments may occur depending on the rater’s level of experience and scale interpretation. Recently, researchers have been developing medical training simulators that mimic hypertonicity to aid the training of these clinician learners. However, there is a lack of quantitative data representing the kinetic and kinematic characteristics of these abnormal muscle behaviors. Thus, we developed a portable measurement device (the PVRM – Position, Velocity, and Resistance Meter) that measures the joint angle, velocity, and muscle resistance of the upper-arm extensor and flexor muscles. In Study 1, the accuracy and reliability of the PVRM was validated by comparing its measurements to a commercial dynamometer (Biodex), a gold standard for measuring biomechanical data. The PVRM measurements were similar to the gold standard Biodex measurements during the passive flexion movement, since the residuals for all measurements were between 1-13%. Therefore, the PVRM was able to quantify behavioral features of spasticity (e.g., catch-release behavior), rigidity (e.g., uniformly elevated muscle tone), and healthy (e.g., no muscle resistance) subjects. In Study 2, we conducted a clinical study of 38 participants using the validated PVRM to establish a database quantifying different levels of spasticity (n=15, MAS 1-4); rigidity (n=11, UPDRS 1-3), and normal healthy (n=12) behavior of the biceps and triceps during passive flexion and extension of the elbow. Spasticity subjects demonstrated stretch speed and MAS score dependent hypertonia marked by a catch-release behavior, resulting in a convex parabolic stretch speed profile. Rigidity subjects exhibited uniformly increased muscle tone that was dependent on UPDRS score but independent of stretch speed. The PVRM can provide a database for development of physical training simulators to realistically mimic hypertonicity and serve as a clinical measurement tool to reliably quantify the type and degree of hypertonicity