The effects of spasticity on gait: A comparison between predictive simulations and expert consensus

Abstract

Spasticity can have a detrimental effect on gait, yet its causal link to gait abnormalities remains unclear. One approach to evaluate the impact of spasticity is to use predictive gait simulations, and another approach is to rely on expert consensus regarding how muscle-specific spasticity affects gait. Currently, neither is fully validated, and it is unclear how these two approaches align. We aimed to compare kinematic gait features according to expert consensus with kinematic effects of muscle-specific spasticity using predictive gait simulations, exploring three modelling approaches: velocity-based, force-based, and a combination of both. We employed a predictive simulation framework with a planar neuromusculoskeletal model, driven by reflex-based control. Spasticity was modelled in four muscles, the soleus, gastrocnemius, rectus femoris, and hamstrings, and individually introduced into our healthy model by increasing reflex gains of the specific feedback mechanism(s). Resulting kinematics were compared with the reference healthy simulated kinematics and checked for the occurrence of expert-based gait features. Overall, 15 out of 21 gait features were present in our simulated kinematics, suggesting good alignment with expert consensus. Kinematic gait features not described by expert consensus were found in hamstrings and rectus femoris simulations. Our combined velocity- and force-based spasticity model showed the best alignment with expert consensus compared to velocity-based and force-based models. This study shows how predictive simulations align with current clinical belief and contribute to a better understanding of the mechanisms underlying spasticity.