Simulated Clinical Triage of Modified Tardieu Test for Lower Limb Spasticity

Developing simulated clinical triage capabilities in-silico on neuro-musculoskeletal models is crucial for creating virtual moving patients. In this study, we demonstrate a novel simulation of the Modified Tardieu Test on a neuro-musculoskeletal model of the lower limb for exploration of essential neuro-musculoskeletal mechanisms underlying the clasp-knife spasticity. We used a modified version of an open source musculoskeletal model in OpenSim, integrated with a basic spinal circuitry comprising
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motor neurons, stretch reflex circuits, and afferent feedback loops. The spasticity test was simulated by passively jerking the limb at varying speeds at the knee joint. Neural parameters of model were empirically adjusted to replicate healthy and spastic physiologies. Further, we also tested validity of the obtained neural control solution by introducing slight time jitters (± 50 ms/100ms) to the inputs of each knee extensor/flexor muscle. The simulations reproduced characteristic knee-joint profiles and velocities reported in literature, validating the model. We also found that the manifestation of the clasp-knife effect was sensitive to the timing of the extensor neural control signals but robust to the jitter of the flexor neural control signals. The computational framework presented here provides insight into the role of spinal circuitry in generating velocity-dependent hyper-excitability leading to spastic behavior. Our work lays the foundation for a biologically realistic model of lower limb spasticity with triaging capabilities. Ultimately, this work aims to establish an in-silico virtual platform for researchers and clinicians to test, monitor, and develop more effective treatment protocols for spasticity and neuro-muscular disorders.