Shanshan Chen, Christopher L. Cunningham, John Lach

1. Enabling Longitudinal Assessment of Ankle-foot Orthosis Efficacy for Children with Cerebral Palsy Shanshan Chen, Christopher L. Cunningham, John Lach Charles L. Brown Dept. of Electrical & Computer Engineering Bradford C. Bennett Motion Analysis and Motor Performance Lab Department of Orthopedic Surgery UVA Center for Wireless Health

2. Cerebral Palsy • Neuromuscular Disorder • Wide Spectrum • Pathological Gait Pattern • How to Treat? • Surgeries: • Muscle lengthening/transferring • Ankle-foot orthosis (AFO) • Very popular Severe Crouch Gait by OpenSim Children with equinus pattern gait (A) and crouch pattern gait (B) deformity

3. Uncertain AFO Efficacy • However.. • Does AFO really help? • How much does it help? • What happens in real life? • Patient Self-Report? • Unreliable • Can’t provide a continuous document Quantitative Measure Continuous, Longitudinal Study

4. Current Clinical Approach • In-lab Optical Motion Capture System • Vicon® instrumented gait lab • High precision, industrial standard • Limitations • Expensive • In-clinic, unnatural environment • Inconvenient to use due to many markers • Discontinuous data if marker drops • Line of sight • Discontinuous data if sight is blocked • Short-term data • A few cycles of gait data • No idea what’s going on outside the lab

5. Inertial BSNs in Gait Analysis • Inertial Body Sensor Networks (BSNs) • Promising Platforms for Portable Gait Analysis • Fall risks assessment • Knee joint angle tracking • Gait speed estimation • Less Invasive and More Wearable • Potential for continuous longitudinal analysis TEMPO 3.1 System 6 DOF motion sensing a wrist watch form factor Developed by the INERTIA • Apply for assessing AFO efficacy • Mold the sensors in the AFOs!!

6. Project Description • Lay the groundwork for a continuouslongitudinal study for children with CP • For the first time, evaluate efficacy of AFO in the long-term, in the real world • Tailor AFOs for each individual • Employ Inertial BSNs for Assessing AFO Efficacy • Design a TRUE continuous, longitudinal monitoring system • Enhancing the ease of use • Molding the inertial BSNs in the AFO • Designing user friendly interface • Elongating battery life • Track gait parameters accurately for valid analysis • Enabling Study • Addressing technical challenges posed by specific applications • Validation of methodology against Vicon®

7. Enabling Study Objectives • Overcome Technical Challenges • Spatial Parameters Extraction • Integration drift • Mounting error • Pathological Gait • Multi-plane movement • Irregular gait pattern • Validate on Real Subjects • Coordination Challenges • Difficult for CP subjects to walk • Synchronization between Vicon® system and TEMPO system

8. Outline • Medical Background in Quantitative Assessment • Methodology to Overcome Technical Challenges • Initial Experiments on Healthy Subject • Validation Experiments on CP Subjects • Future Work • Conclusion

9. Quantitative Assessment • Medical Hypothesis for AFO • Help to correct pathological gait by limiting out-of-plane motion and increase the stability • Limit the excessive knee flexion and resisting dorsiflexion for the crouch gait • Limit the excessive plantar flexion for the equinus gait and promote heel-strike • Ankle Joint Angle as Primary Gait Parameter

10. With and Without AFO Comparison -- Ankle Joint Angle

11. With and Without AFO Comparison -- Shank Angular Velocity

12. Outline • Medical Background in Quantitative Assessment • Methodology to Overcome Technical Challenges • Initial Experiments on Healthy Subject • Validation Experiments on CP Subjects • Future Work • Conclusion

13. Angle Extraction from Inertial BSNs • Accelerometer • Provide inclination information of the sensor node by utilizing gravitational factor • Gyroscope • Indicates the angular velocity of the inertial frame • Differential Inclination of Shank and Foot • Ankle_Angle = Shank_Angle – Foot_Angle

14. Minimizing Integration Drift • Complimentary Filter • Accelerometer is good at long term displacement estimation • – low pass, keep low frequency component • Gyroscope is good at short period displacement estimation • – high pass, keep motion change • Fusing/Combining information of accelerometer and gyroscope sensors • 1stOrder Butterworth filter, • Time Domain:

15. Minimizing Mounting Error • Mounting Calibration • Sensor Alignment • Sensors are not affixed to the body in the global coordinate • Coordinates re-mapping • Rotation Matrix • Euler rotation sequence • Obtain compensating angles from the rotation matrix • Sensor coordinates map back to the desired coordinates

16. Compensating for Multi-plane Motion • Multi-plane Movement • Severe motion on planes apart from sagittal plane • Multi-axis rotation obtained by looking at the 3-axis rotation • Method • Rotations do not commute with each other • Derive Euler rotation rate from gyroscope signal • Provide less error but when the sampling rate is sufficiently high, the gyroscope rate is near Euler rotation rate Severe Crouch Gait by OpenSim

17. Outline • Medical Background in Quantitative Assessment • Methodology to Overcome Technical Challenges • Initial Experiments on Healthy Subject • Validation Experiments on CP Subjects • Future Work • Conclusion

18. Initial Experiments on Healthy Subject • Prep for Experiments on CP Subjects • Validating methodology for further development • Solving the practical issues in the experiments • Controlling gait variables • Experiment Setup • One healthy subject • Synchronization procedure • Walked on the treadmill for 1 minute • 3 Gait Patterns, with/without AFO comparison • Normal • Simulated Crouch Gait • Simulated Equinus Gait

19. Healthy Subject -- Normal Gait

20. Healthy Subject-- Simulated Crouch Gait

21. Healthy Subject – Simulated Equinus Gait

22. Outline • Medical Background in Quantitative Assessment • Methodology to Overcome Technical Challenges • Initial Experiments on Healthy Subject • Validation Experiments on CP Subjects • Future Work • Conclusion

23. Validation Experiments on Children with CP • Experiment Setup • 4 CP Subjects Wearing AFOs • Vicon® markers and TEMPO instrumented at the same time • On Ground Walking for Several Trials • Within the range of the Vicon® cameras • About 5 meters each trial • Unexpected Challenges • Validation Challenge • Walking aid devices block the line of sight • A few cycles – not easy for CP subjects to get on treadmill • Mounting Calibration Challenge • CP subject with crouch gait has difficulty to stand straight and still • Need of assistance from the research staff for holding the subject’s shanks

24. Ankle Joint Angle Validation

25. Ankle Joint Angle Validation (contd.)

26. Ankle Joint Angle Range Validation

27. Shank Angular Velocity Validation

28. Enabling Study Outcomes • Sufficient Accuracy for Key Gait Parameters Extraction • Validated against Vicon® for Children with CP Validated!

29. Future Work • Future Plan for CP Subject Study • Fabricate AFOs and non-AFOs • with compartments sized for molding TEMPO • Instruct Children with CP • wear AFO/non-AFO as they typically do • charge the device and upload data to the remote site • Future Plan for Technology Updates • Molding Inertial Sensors into the AFOs • Data Streaming Unnecessary • Data caching for opportunistic offloading • Ensuring battery life • More Analysis Enabled to Assess AFO Efficacy • Gait Speed • Phase Portrait -- Gait Stability and Complexity

30. Phase Portrait Comparison – Healthy Subject

31. Phase Portrait Comparison– CP subject

32. Conclusion AFO Manufacturers • Validation of Methodology • Enabled Continuous Longitudinal Study • Improve Patient Outcomes • Tailor AFO for each individual Physicians Caregivers Network EMR Server Medical Researchers

33. Thanks!