Present Study Patient Specific Motion Modeling and Assistive Devices S Russell, P Sheth, B Bennett, P Allaire, M Abel University of Virginia, Motion Analysis and Motor Performance Laboratory, Charlottesville, VA. Develop patient specific full body gait model Develop patient specific full body gait model Develop applied joint torques from desired Angular Momentum Develop applied joint torques from desired Angular Momentum Implementation of newly developed foot model Implementation of newly developed foot model Application and validation of Optimized contact model between foot and floor Application and validation of Optimized contact model between foot and floor Angular Momentum used to develop stable walking in bipedal gait models (Goswami, Popovic) Angular Momentum used to develop stable walking in bipedal gait models (Goswami, Popovic) Previously used to: Previously used to: Determine energy lost at heel strike/foot contact Determine energy lost at heel strike/foot contact Control strategy for full body model in single support Control strategy for full body model in single support 3-D kinematics collected via Vicon implementing a 38 marker Helen-Hayes full body set 3-D kinematics collected via Vicon implementing a 38 marker Helen-Hayes full body set 3 subjects with no history of lower extremity pathology were used to develop/validate patient specific models 3 subjects with no history of lower extremity pathology were used to develop/validate patient specific models Stable walking patterns are predicted using the angular momentum about the full body CoM as the high level control Stable walking patterns are predicted using the angular momentum about the full body CoM as the high level control Analysis found angular momentum computed from experimentally measured kinematics was invariant with speed (+ 20%) Analysis found angular momentum computed from experimentally measured kinematics was invariant with speed (+ 20%) Consistent with published data (Popovic) Consistent with published data (Popovic) Allows simulation of various speed from same angular momentum control matrix [A] Allows simulation of various speed from same angular momentum control matrix [A] Subject specific models make no assumption regarding symmetry and model entire gait cycle Subject specific models make no assumption regarding symmetry and model entire gait cycle Our research has found that children with Cerebral Palsy walk with angular momentum patterns similar to typical walkers Our research has found that children with Cerebral Palsy walk with angular momentum patterns similar to typical walkers Extension of this work is under way Extension of this work is under way Full 3-D simulations Full 3-D simulations Prediction pathologic gait Prediction pathologic gait Acknowledgements The authors would like to thank the staff at the Gait and Motion Analysis Lab, Kluge Children’s Rehabilitation Center at the University of Virginia, where experiments were conducted. This work was supported in part by NSF grant INTRODUCTION RESULTS (cont) DISCUSSION METHODS (cont) RESULTS Angular Momentum Control METHODS Tested Subjects Simulations completed successfully implementing, patient specific model, foot/floor contact model, and PD control for both single and double support phase Simulations completed successfully implementing, patient specific model, foot/floor contact model, and PD control for both single and double support phase Model successfully predicted gait kinematics and ground reaction force for individual patients Model successfully predicted gait kinematics and ground reaction force for individual patients Plots show lower extremity joint kinematics of a single patient. Results shown include experimentally measured joint angles for the ankle, knee, and hip joint. Also shown are the lower extremity joint angles predicted using the patient specific model, revised foot model, improved floor contact model, and angular momentum based PD control for joint torques Full body model developed for Full body model developed for each patient via MSC.Adams each patient via MSC.Adams using LifeMod using LifeMod Patient anthropometrics used Patient anthropometrics used with the GeBOD data base to with the GeBOD data base to create patient specific models create patient specific models Model Model 19 body segments 19 body segments 16 joints 16 joints Full 3-D with motion Full 3-D with motion constrained to sagittal plane constrained to sagittal plane Ground Contact Ground Contact Ground placement optimized resulting in GRF equaling Body weight Ground placement optimized resulting in GRF equaling Body weight Coulomb friction applied between floor and foot geometries Coulomb friction applied between floor and foot geometries Contact parameters (stiffness/damping) optimized in both planes to match experimentally measured GRF Contact parameters (stiffness/damping) optimized in both planes to match experimentally measured GRF Similar solution parameters suggest optimization process is not mandatory Similar solution parameters suggest optimization process is not mandatory Model Development Foot Model Foot Model Previous model consisted of Previous model consisted of only heel and toe ellipsoids only heel and toe ellipsoids Resulted in piece wise motion Resulted in piece wise motion of modeled CoP of modeled CoP Non-smooth GRF Non-smooth GRF New model includes contact New model includes contact ellipsoids along metatarsals ellipsoids along metatarsals connecting heel/toe ellipsoids connecting heel/toe ellipsoids Smooth/continuous GRF Smooth/continuous GRF Facilitates smooth CoP motion in Facilitates smooth CoP motion in both sagittal and frontal planes both sagittal and frontal planes Angular momentum of each segment about the body CoM calculated and averaged for each test subject Angular momentum of each segment about the body CoM calculated and averaged for each test subject Data used to populate 19xN matrix [A] where: Data used to populate 19xN matrix [A] where: N = # data points over gait cycle N = # data points over gait cycle PD control used to determine joint torques for each point of gait cycle, 1,2,…N PD control used to determine joint torques for each point of gait cycle, 1,2,…N Simulations run using angular momentum [A] as negative feedback for PD control resulting in minimized error between desired and simulated angular momentum Simulations run using angular momentum [A] as negative feedback for PD control resulting in minimized error between desired and simulated angular momentum Angular Momentum Control Comparison of actual patient vertical ground reaction force, measured experimentally, and the vertical component of the ground reaction force predicted by the model using Angular momentum control and the new foot and ground contact model. References Goswami, A., Kallen, V. (2004). Proc IEEE ICRA ’04, Popovic, M., et al. (2004). Proc IEEE ICRA ’04, Popovic, M., et al. (2004). Proc IEEE/RSJ IROS ’04,

Present Studies Patient Specific Motion Modeling and Assistive Devices S Russell, P Sheth, B Bennett, P Allaire, M Abel University of Virginia, Motion Analysis and Motor Performance Laboratory, Charlottesville, VA. Develop plantar flexion assist ankle foot orthosis (AFO) to promote heel strike while facilitating 3 rockers of stance Develop plantar flexion assist ankle foot orthosis (AFO) to promote heel strike while facilitating 3 rockers of stance Develop passive brace to store energy lost at heel strike and return it during pre swing Develop passive brace to store energy lost at heel strike and return it during pre swing Develop motorized walker to predict gait events and assist subjects in walking and turning Develop motorized walker to predict gait events and assist subjects in walking and turning Develop an AFO which limits plantar flexion during swing due to conditions such as equinus or drop foot Develop an AFO which limits plantar flexion during swing due to conditions such as equinus or drop foot Allow patient kinematics to exploit all three rockers during stance (Figure 1) Allow patient kinematics to exploit all three rockers during stance (Figure 1) Development of “real time” prediction of Gait events from forces applied to walker handles during walking Development of “real time” prediction of Gait events from forces applied to walker handles during walking Development of shared control algorithm to control electric motors for desired walker motion Development of shared control algorithm to control electric motors for desired walker motion Hold walker position fixed in cases of impending fall (instability) Hold walker position fixed in cases of impending fall (instability) Interject energy during strategic gait events (push off) Interject energy during strategic gait events (push off) Facilitate directional control of walker Facilitate directional control of walker Negate additional work of dragging a walker during gait Negate additional work of dragging a walker during gait INTRODUCTION Smart WalkerEnergy Return AFOPlantar Flexion Assist AFO Objectives Energy stored at heel strike Energy stored at heel strike Body weight compresses springs Body weight compresses springs Springs held in compression by multi-tooth ratchet system Springs held in compression by multi-tooth ratchet system Tension in cables released to facilitate full range of motion Tension in cables released to facilitate full range of motion Energy returned during push off Energy returned during push off Body rotates forward over foot (2 nd rocker) Body rotates forward over foot (2 nd rocker) Foot is dorsi-flexed taking slack out of cable Foot is dorsi-flexed taking slack out of cable Weight in on ball of foot activating mechanism to release springs Weight in on ball of foot activating mechanism to release springs Springs create plantar flexion moment about ankle joint via cables Springs create plantar flexion moment about ankle joint via cables Energy added from ankle plantar flexion at push off for CP gait typically 15-20% less than normal gait Energy added from ankle plantar flexion at push off for CP gait typically 15-20% less than normal gait Develop an AFO to store the energy lost during heel strike and return the energy later in gait cycle (i.e. push off) Develop an AFO to store the energy lost during heel strike and return the energy later in gait cycle (i.e. push off) Return.4 J/kg of energy to gait at push off (15% total normal energy added at push off) Return.4 J/kg of energy to gait at push off (15% total normal energy added at push off) Allow patient kinematics to exploit all three rockers during stance (Figure 1) Allow patient kinematics to exploit all three rockers during stance (Figure 1) Objectives Cerebral Palsy 764,000 people in the United States have symptoms of Cerebral Palsy (CP) 764,000 people in the United States have symptoms of Cerebral Palsy (CP) Metabolic costs of walking 2-3 times higher in individuals with CP Metabolic costs of walking 2-3 times higher in individuals with CP 50% of people with CP are prescribed Ankle Foot Orthotics (AFO) 50% of people with CP are prescribed Ankle Foot Orthotics (AFO) Previous research equivocal on effectiveness of AFO’s Previous research equivocal on effectiveness of AFO’s Preform real-time prediction of gait events (i.e. heel strike, toe off) via forces applied to walker handles Preform real-time prediction of gait events (i.e. heel strike, toe off) via forces applied to walker handles Create shared control of a motorized posterior walker to facilitate better walking in children with CP Create shared control of a motorized posterior walker to facilitate better walking in children with CP Objectives Figure 1. 1 st Rocker represents rotation about the heel at initial heel contact allowing the foot to lay flat, 2 nd Rocker allows the body to progress forward rotating about the ankle with the foot flat in stance, and the 3 rd rocker allows the subject to rotate onto the ball of there foot to facilitate push off during pre swing. Solid ankle AFO’s and posterior leaf spring (PLS) restrict or inhibit one or more kinematic rockers Solid ankle AFO’s and posterior leaf spring (PLS) restrict or inhibit one or more kinematic rockers Hinged AFO’s facilitate rockers but cannot inhibit foot drop or equinus Hinged AFO’s facilitate rockers but cannot inhibit foot drop or equinus Current AFO’s Based on a double upright AFO with dual action joints Based on a double upright AFO with dual action joints Patient specific conical compression springs located between foot bed and sole of shoe Patient specific conical compression springs located between foot bed and sole of shoe Ankle plantar flexion compresses the springs via the cable, moment arm, and pulleys Ankle plantar flexion compresses the springs via the cable, moment arm, and pulleys Spring tension is adjusted to apply patient specific plantar flexion assist during swing phase Spring tension is adjusted to apply patient specific plantar flexion assist during swing phase In stance springs are compressed as weight is transferred forward releasing tension on moment arm facilitating full range of motion and all 3 rockers In stance springs are compressed as weight is transferred forward releasing tension on moment arm facilitating full range of motion and all 3 rockers Current Solution Design Springs Pulleys Moment Arm Assist Adjustors Upright Shoe Hinge Cable Sole An additional benefit of the design is the energy return applied during pre swing to aid push off as the springs decompress as body weight is removed An additional benefit of the design is the energy return applied during pre swing to aid push off as the springs decompress as body weight is removed Solid ankle AFO’s are unable to return energy to gait cycle while PLS, ground reaction, and carbon toe off AFO’s store and return energy at push off but do so by inhibiting the 2 nd rocker Solid ankle AFO’s are unable to return energy to gait cycle while PLS, ground reaction, and carbon toe off AFO’s store and return energy at push off but do so by inhibiting the 2 nd rocker Current AFO’s Current Solution Design Post-processing prediction of gait events from handle forces validated using VICON motion analysis Post-processing prediction of gait events from handle forces validated using VICON motion analysis Implementation of shared control on steering angle to control anterior walker trajectories Implementation of shared control on steering angle to control anterior walker trajectories Previous Solutions Current Solution Design Ratchet Mechanism Upright Hinge Moment Arm Tension Adjustor Springs Release Mechanism Cable Release Mechanism