Dynamic Musculoskeletal Simulation of a Passive Exoskeleton for Simulating Contracture

Gait assessment scores are used for quantifying the abnormalities in the gait. Evaluation of the performance of these scores is a must for their clinical acceptance. However, current methods of assessing the performance of the gait assessment scores for clinically relevant gait abnormalities are prone to error. For example, values of intra-observer reliability, inter-observer reliability and sensitivity calculated for a gait assessment score change with the population of patients and observers. Therefore, there is a need for a methodology for replicating musculoskeletal deformations such as contracture in healthy individuals for objectively evaluating the performance of gait assessment scores with variable severity of musculoskeletal deformations. In this study, a series of dynamic musculoskeletal simulations are performed to simulate and verify a mathematical model of a passive exoskeleton for simulating contractures. The proposed model achieved a root mean square error of 1.864° and a correlation of coefficient of 0.984 while testing on five unique combinations of linear and non-linear torques and seven degrees of severity of hamstring contracture. To understand the tolerance of the proposed model to environmental noises, its performance is also tested at various perturbations. The results indicate that a passive exoskeleton attached to an unimpaired musculoskeletal model can accurately simulate the contracture of the targeted muscles. Clinical relevance - The proposed methodology has a utility in evaluating performances of gait assessment scores and understanding the effect of contractures on biomechanics of gait.