The Effect of Femoral Anteversion and Tibial Torsion on Simulation of Cerebral Palsy Gait

Musculoskeletal modeling and dynamics simulations are common tools used to analyse gait in patients with Cerebral Palsy (CP). These musculoskeletal models are usually generic models based on anatomical measurements obtained from cadavers, hence no subject characteristics are included. It is important to understand the accuracy of using a generic musculoskeletal model when analysing impaired gait to better comprehend the outcome which can lead to enhanced gait analysis for CP. The purpose of this study was to determine if and how a musculoskeletal model, including femoral anteversion and tibial torsion, will improve a simulation of CP gait. Deformed musculoskeletal models including femoral anteversion and/or tibial torsion and a generic musculoskeletal model were applied to artiﬁcial datasets representing the same deformation as in the deformed model. The model outputs that were studied are marker tracking errors, simulated joint angles, muscle-tendon length and moment arms of the psoas, gluteus medius, gastrocnemius and tibialis anterior in a static pose and during simulation of gait. The models were also tested with gait data for ﬁve CP subjects. A generic and a deformed model were applied to gait data for each the subjects. The same model outputs were analysed and compared between the models as for the artiﬁcial datasets. Eﬀects of ﬁtting a generic musculoskeletal model on data including bone deformations was demonstrated with the artiﬁcial data. Although, ﬁtting the generic model and the deformed model to the ﬁve CP subjects did show the same eﬀects as for the artiﬁcial data we can not conclude that including femoral anteversion and tibial torsion in a musculoskeletal model will improve simulation of CP gait since these eﬀect were on a small scale and could be due to other factors than the bone deformations. This thesis is submitted for the degree of Master of Science at the Delft University of Technology, titled: The eﬀect of femoral anteversion and tibial torsion on simulation of cerebral palsy gait. First, an overview of the prerequisite theory is presented. Then the creation of the musculoskeletal model and the experimental setup are introduced. Finally, the results are presented and discussed. This thesis was conducted under the supervision of Dr. van der Krogt. The subject data used in this these was provided by another study called Model-Driven European Paediatric Digital Repository (MD-peadigree). Abstract Musculoskeletal modeling and dynamics simulations are common tools used to analyse gait in patients with Cerebral Palsy (CP). These musculoskeletal models are usually generic models based on anatomical measurements obtained from cadavers, hence no subject characteristics are included. It is important to understand the accuracy of using a generic musculoskeletal model when analysing impaired gait to better comprehend the outcome which can lead to enhanced gait analysis for CP. The purpose of this study was to determine if and how a musculoskeletal model, including femoral anteversion and tibial torsion, will improve a simulation of CP gait. Deformed musculoskeletal models including femoral anteversion and/or tibial torsion and a generic musculoskeletal model were applied to artiﬁcial datasets representing the same deformation as in the deformed model. The model outputs that were studied are marker tracking errors, simulated joint angles, muscle-tendon length and moment arms of the psoas, gluteus medius, gastrocnemius and tibialis anterior in a static pose and during simulation of gait. The models were also tested with gait data for ﬁve CP subjects. A generic and a deformed model were applied to gait data for each the subjects. The same model outputs were analysed and compared between the models as for the artiﬁcial datasets. Eﬀects of ﬁtting a generic musculoskeletal model on data including bone deformations was demonstrated with the artiﬁcial data. Although, ﬁtting the generic model and the deformed model to the ﬁve CP subjects did show the same eﬀects as for the artiﬁcial data we can not conclude that including femoral anteversion and tibial torsion in a musculoskeletal model will improve simulation of CP gait since these eﬀect were on a small scale and could be due to other factors than the bone deformations. capacity of muscles to accelerate the joints during gait and other movements. Models including femoral anteversion or tibial torsion separately have both provided accurate estimates when analysing impaired gait. However, the eﬀects on simulation of CP gait by including both of these deformations in the same model and comparing with results from a generic model is lacking in the literature. The eﬀects of applying a generic model to impaired gait with either femoral anteversion and/or tibial torsion in OpenSim is also unknown, and an application for OpenSim to deform these bones is not available. By including bone deformation in a musculoskeletal model a more representative location of the muscle attachments is acquired but it is yet unknown how the combined modelling of femoral anteversion and tibial torsion aﬀects simulations of CP gait. The overall goal of this study was to determine if, and how, a musculoskeletal model including femoral anteversion and tibial torsion will improve simulation of CP gait. Two types of musculoskeletal models were used, a generic musculoskeletal model (GM) and deformed musculoskeletal models (DM) (Fig: 1). The GM was used without including any patient-speciﬁc bone geometry. The DM either included one of the deformations, femoral anteversion (DM-FA) or tibial torsion (DM-TT), or both of them (DM-FATT). The deformation methods were based on previously men- tioned methods by Arnold et al. and Hicks et al. The speciﬁc aims were ﬁrstly, to determine the theoretical eﬀects of including femoral anteversion and/or tibial torsion in a musculoskeletal model when simulating static pose and gait. Secondly, to determine the eﬀects of including femoral anteversion and tibial torsion in a musculoskeletal model when simulating gait for ﬁve CP subjects. The marker tracking errors, joint angles, moment arm and muscle-tendon length of the gluteus medius, psoas, gastrocnemius, and the tibialis anterior were used for evaluation for both of these aims. were moved to match with the experimental markers. The inverse kinematics tool in OpenSim was used to generate simulations of the gait trials. This tool positions the musculoskeletal model in a pose for each time step of the gait by solving the same weighted least-squares problem as mentioned above. Each marker was also assigned a weight before solving this problem, the motion segment markers were assigned a higher values for more signiﬁcance than the other markers since these markers are less likely to be inﬂuenced by muscle and other soft tissue movements during motion [21].