Simulation of soft tissue loading from observed movement dynamics

Abstract

An understanding of in vivo soft tissue loading is essential for investigating the causes of traumatic injury, progression of degenerative joint disease, and options for orthopedic treatment. Modern motion analysis technologies can be used to observe movement dynamics and characterize resultant joint loads. However, technologies for directly measuring the loads on in vivo soft tissues (e.g., ligament, tendon, and cartilage) generally require invasive techniques and thus are impractical for widespread use. In this chapter, we review two computational modeling approaches for characterizing soft tissue loads from observed movement dynamics. In the traditional sequential simulation approach, linked-segment dynamic musculoskeletal models are first solved for muscle and resultant joint loading. These loads are then applied as boundary conditions on a more detailed model of the joint to estimate loading and deformation of ligament and cartilage tissues. The primary limitation of the sequential approach is that it decouples movement dynamics and joint mechanics, making it infeasible to predict how muscle coordination may adapt to changes in soft tissue behavior. To overcome this limitation, concurrent simulation approaches have been introduced, which enable simultaneous solution of muscle forces and soft tissue mechanics underlying human movement. We demonstrate the advantage of the concurrent approach to directly probe inherent coupling between muscle coordination, joint kinematics, cartilage contact pressure, and ligamentous behavior that can arise with soft tissue damage. We conclude with suggestions for further development and use of concurrent simulation approaches that could greatly extend our ability to investigate both surgical and rehabilitative treatments of musculoskeletal pathologies.