Investigation of the dependence of joint contact forces on musculotendon parameters using a codified workflow for image-based modelling

The generation of subject-specific musculoskeletal models of the lower limb has become a feasible taskthanks to improvements in medical imaging technology and musculoskeletal modelling software.Nevertheless, clinical use of these models in paediatric applications is still limited for what concernsthe estimation of muscle and joint contact forces. Aiming to improve the current state of the art, amethodology to generate highly personalized subject-specific musculoskeletal models of the lower limbbased on magnetic resonance imaging (MRI) scans was codified as a step-by-step procedure and appliedto data from eight juvenile individuals. The generated musculoskeletal models were used to simulate 107gait trials using stereophotogrammetric and force platform data as input. To ensure completeness of themodelling procedure, muscles’ architecture needs to be estimated. Four methods to estimate muscles’maximum isometric force and two methods to estimate musculotendon parameters (optimal fiber lengthand tendon slack length) were assessed and compared, in order to quantify their influence on the models’output. Reported results represent the first comprehensive subject-specific model-based characterizationof juvenile gait biomechanics, including profiles of joint kinematics and kinetics, muscle forces and jointcontact forces. Our findings suggest that, when musculotendon parameters were linearly scaled from areference model and the muscle force-length-velocity relationship was accounted for in the simulations,realistic knee contact forces could be estimated and these forces were not sensitive the method used tocompute muscle maximum isometric force.