1. OpenSim Workshop March 2013 Simulation of Obese Locomotion Biomechanics Workshop Goals: -Investigate the effects of individual muscle strength scaling on muscle force production and joint reaction forces -Refine our weighted static optimization API code to read in settings from an XML file -Knee able to resolve med-lat joint contact force distribution -Must incorporate knee alignment >> Modify Knee Model -Discuss predictive optimization approaches (over beer)

2. OpenSim Workshop March 2013 Modeling Static Knee Alignment: Motivation Obese children have ~3X greater prevalence of knee malalignment vs. NO Malalignement as Obese adult >> much greater risk for development and progression of OA We want to quantify both the magnitude and the distribution of the knee joint contact force

3. OpenSim Workshop March 2013 Modeling Static Knee Alignment What is the correct anatomical alignment? ?

4. OpenSim Workshop March 2013 Modeling Static Knee Alignment For this exercise, we kept the tibiofemoral joint parallel to the ground Added two bodies (femoral condyles, tibial plateau) Updated joint definitions (articulations) θ Varus alignment

5. OpenSim Workshop March 2013 Modeling Static Knee Alignment Also made a model with valgus alignment

6. OpenSim Workshop March 2013 Check: Make sure muscles aren’t passively stretched i.e. musculo-tendon unit is the same between a neutral and malaligned knee Modeling Static Knee Alignment e.g. Semitendinosus

7. OpenSim Workshop March 2013 Modeling Static Knee Alignment Reran IK>RRA>SO>JR for Valgus, Varus, and Neutral Alignment

8. OpenSim Workshop March 2013 Modeling Static Knee Alignment Axial Force Largest with Varus alignment (Not Expected, I expected neutral) Result of forcing alignment on neutral subject

9. OpenSim Workshop March 2013 Modeling Static Knee Alignment Knee Abd/Add Moment Largest with Varus alignment (Expected, Obvious) Add Abd

10. OpenSim Workshop March 2013 Proof of Concept: Can incorporate radiographic knee alignment to better understand loading in future childhood obesity study Take home message: Critical to incorporate frontal plane knee alignment if you intend to calculate medial-lateral distribution! Future: Balance forces and moments to resolve *approximate* medial-lateral distribution Incorporate med-lat calculation in a JR plugin Modeling Static Knee Alignment

11. OpenSim Workshop March 2013 Thank you, OpenSim Team!