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 1 Bradford C. Bennett Motion Analysis and Motor Performance Lab Department of Orthopedic Surgery UVA Center for Wireless Health

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 2

3 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 Uncertain AFO Efficacy Continuous, Longitudinal Study Quantitative Measure

Current Clinical Approach 4 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

Inertial BSNs in Gait Analysis 5 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!!

Project Description Lay the groundwork for a continuous longitudinal 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® 6

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 7

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

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 9

With and Without AFO Comparison -- Ankle Joint Angle 10

With and Without AFO Comparison -- Shank Angular Velocity 11

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

Angle Extraction from Inertial BSNs 13

Minimizing Integration Drift 14

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 15

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 16 Severe Crouch Gait by OpenSim

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

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 18

Healthy Subject -- Normal Gait 19

Healthy Subject-- Simulated Crouch Gait 20

Healthy Subject – Simulated Equinus Gait 21

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

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 23

Ankle Joint Angle Validation 24

Ankle Joint Angle Validation (contd.) 25

Ankle Joint Angle Range Validation 26

Shank Angular Velocity Validation 27

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

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 29

Phase Portrait Comparison – Healthy Subject 30

Phase Portrait Comparison – CP subject 31

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

THANKS! 33