Simulation of Exoskeleton Alignment and its Effect on the Knee Extensor and Flexor Muscles

This study presents the analysis of different knee joint impairments and their effects on the knee extensor and flexor muscles. Joint impairments can result from stroke, musculoskeletal diseases, or misalignment of an attached exoskeleton joint. Understanding the correlation between parameters involved in joint movement mechanisms as well as force interactions could provide insight to establish an appropriate design for exoskeletons. Joints can be powered or even be rectified in terms of alignment by exoskeletons to help a patient recover quickly. For the study, OpenSIM 4.0 was used to generate models and simulations of the human musculoskeletal structure with and without introduced knee joint impairments along the sagittal and transverse directions. A scenario to simulate the constraints of an exoskeleton designed with a single hinge joint to mimic the knee joint was also considered. Alterations to the knee joint axis within the range of +5.00 to -6.40 mm would result in a meaningful yet not a significant change in muscle stresses; the simulation outputs indicate that constraining the knee joint motion to the sagittal plane will only increase the force generated by the vastus lateralis muscle up to 4.3%.