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R. Hainisch, Z. Karim, A. Kranzl, M. Gföhler, MG Pandy:
"Joint Moments in Children with Cerebral Palsy based on Biomechanical Models";
Talk: ESMAC 2011 Europ. Soc. of Gait Analysis for Adults & Children, Vienna; 2011-09-15 - 2011-09-17; in: "20th Annual Meeting of ESMAC", (2011), 44.

Introduction
Cerebral Palsy (CP) is resulting from a static injury to the developing brain. An abnormal motor control with associated delay in onset of walking and an abnormal gait pattern (crouch gait) are commonly characteristics to this type of injury. Subject specified 3-dimensional computational models of the musculoskeletal system will be used for the calculation of the muscle function during gait. To asses the models we will use for further simulations we compared the possible net joint moments in several degrees of freedom.

Patients/ Material and methods
We performed gait experiments of 2 children with cerebral palsy and of a control group of 5 age-matched healthy subjects to get motion capture data and ground reaction forces. Electromyography was only recorded from the healthy subjects. For the lower limbs Magnetic-Resonance-Imaging was taken for all subjects. We created musculoskeletal biomechanical models based on a template-model in OpenSim [1]. After scaling of the template model according to anatomical landmarks [2] the parameters of each muscle in the models were customized according to the individual MRI-based anatomical data. The coordinates of the muscles attachment points, where extracted from a manual segmented MR-data-set. This was done by taking into account biased limb positions during image capture [3]. The parameters for the Hill-type [4] muscle-model in particular maximum isometric force, optimal muscle-fiber-length and tendon-slack-length where set according to calculation algorithms described in [3].

Results
We calculated the net joint moments and all individual muscle contributions in the models over a typical range of motion of all joints in the lower limbs with OpenSim. The results were compared to data from a scaled generic model [5].
Even if the net joint moment in CP-children is lower due to weaker muscles the results indicate no significant differences in net joint moment due to biased bone geometry or shifted muscle attachment points in CP-children.

Discussion & Conclusion
We might have to change this calculation and take into account the special physiological conditions in CP muscles. The derived net joint moments only represent the maximum possible joint moment without taking into account passive forces and spasticisms of antagonists.

References
[1] Delp 2007, OpenSim: Open-Source Software to Create and Analyze Dynamic Simulations of Movement. IEEE Transactions on Biomedical Engineering. 54(11)
[2] Hainisch et. al, Scaling of biomechanical models: A comparison of motion tracking markers and anatomical landmarks, 9th International Symposium on computer Methods in Biomechanics and Biomedical Engineering, Valencia 2010.
[3] Hainisch et al, METHOD for Determination of Musculotendon Parameters in A Subject-Specific Musculoskeletal Model of a child based on MRI Data, Proceedings of Euromech Colloquium511, 3/2011
[4] Hill, The heat of shortening and the dynamic constants of muscle. Proceedings of the Royal Society of London Series
[5] Anderson, A dynamic optimisation solution for a complete cycle of normal gait, Dissertation, University of Texas 12/1999

Biomechanics, Joint Moments, Modelling, Cerebral Palsy