Enabling Longitudinal Assessment of Ankle-Foot Orthosis Efficacy for Children with Cerebral Palsy

Enabling Longitudinal Assessment of Ankle-foot Orthosis Efficacy for Children with Cerebral PalsyShanshan Chen, Christopher L. Cunningham, John LachCharles L. Brown Dept. of Electrical & Computer Engineering

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Bradford C. BennettMotion Analysis and Motor Performance LabDepartment of Orthopedic Surgery

UVA Center for Wireless Health 1Cerebral PalsyNeuromuscular DisorderWide SpectrumPathological Gait Pattern

How to Treat?Surgeries:Muscle lengthening/transferringAnkle-foot orthosis (AFO)Very popular

Severe Crouch Gait by OpenSim

Children with equinus pattern gait (A) and crouch pattern gait (B) deformity22 3However..Does AFO really help?How much does it help?What happens in real life?

Patient Self-Report?UnreliableCant provide a continuous document

Uncertain AFO EfficacyContinuous, Longitudinal StudyQuantitative Measure3Current Clinical Approach4In-lab Optical Motion Capture System Vicon instrumented gait labHigh precision, industrial standardLimitationsExpensiveIn-clinic, unnatural environmentInconvenient to use due to many markersDiscontinuous data if marker dropsLine of sight Discontinuous data if sight is blockedShort-term dataA few cycles of gait dataNo idea whats going on outside the lab

4Inertial BSNs in Gait Analysis

5Inertial Body Sensor Networks (BSNs)Promising Platforms for Portable Gait AnalysisFall risks assessmentKnee joint angle trackingGait speed estimationLess Invasive and More WearablePotential for continuous longitudinal analysisTEMPO 3.1 System 6 DOF motion sensinga wrist watch form factorDeveloped by the INERTIA

Apply for assessing AFO efficacyMold the sensors in the AFOs!!5Project DescriptionLay the groundwork for a continuous longitudinal study for children with CPFor the first time, evaluate efficacy of AFO in the long-term, in the real worldTailor AFOs for each individual

Employ Inertial BSNs for Assessing AFO EfficacyDesign a TRUE continuous, longitudinal monitoring systemEnhancing the ease of useMolding the inertial BSNs in the AFO Designing user friendly interfaceElongating battery lifeTrack gait parameters accurately for valid analysis

Enabling StudyAddressing technical challenges posed by specific applicationsValidation of methodology against Vicon66Enabling Study ObjectivesOvercome Technical ChallengesSpatial Parameters ExtractionIntegration driftMounting errorPathological GaitMulti-plane movementIrregular gait pattern

Validate on Real SubjectsCoordination Challenges Difficult for CP subjects to walkSynchronization between Vicon system and TEMPO system

77OutlineMedical Background in Quantitative AssessmentMethodology to Overcome Technical ChallengesInitial Experiments on Healthy SubjectValidation Experiments on CP SubjectsFuture WorkConclusion8Quantitative AssessmentMedical Hypothesis for AFOHelp to correct pathological gait by limiting out-of-plane motion and increase the stabilityLimit the excessive knee flexion and resisting dorsiflexion for the crouch gaitLimit the excessive plantar flexion for the equinus gait and promote heel-strike

Ankle Joint Angle as Primary Gait Parameter

99With and Without AFO Comparison -- Ankle Joint Angle

1010With and Without AFO Comparison -- Shank Angular Velocity

11OutlineMedical Background in Quantitative AssessmentMethodology to Overcome Technical ChallengesInitial Experiments on Healthy SubjectValidation Experiments on CP SubjectsFuture WorkConclusion12Angle Extraction from Inertial BSNs1313Minimizing Integration Drift14

14Minimizing Mounting Error

Mounting CalibrationSensor AlignmentSensors are not affixed to the body in the global coordinateCoordinates re-mapping

Rotation MatrixEuler rotation sequenceObtain compensating angles from the rotation matrixSensor coordinates map back to the desired coordinates1515Compensating for Multi-plane MotionMulti-plane MovementSevere motion on planes apart from sagittal planeMulti-axis rotation obtained by looking at the 3-axis rotation

MethodRotations do not commute with each otherDerive Euler rotation rate from gyroscope signalProvide less error but when the sampling rate is sufficiently high, the gyroscope rate is near Euler rotation rate

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Severe Crouch Gait by OpenSim16OutlineMedical Background in Quantitative AssessmentMethodology to Overcome Technical ChallengesInitial Experiments on Healthy SubjectValidation Experiments on CP SubjectsFuture WorkConclusion1717Initial Experiments on Healthy Subject

Prep for Experiments on CP SubjectsValidating methodology for further developmentSolving the practical issues in the experimentsControlling gait variables

Experiment SetupOne healthy subjectSynchronization procedureWalked on the treadmill for 1 minute3 Gait Patterns, with/without AFO comparisonNormalSimulated Crouch GaitSimulated Equinus Gait

1818Healthy Subject -- Normal Gait

19Healthy Subject-- Simulated Crouch Gait

2020Healthy Subject Simulated Equinus Gait

2121OutlineMedical Background in Quantitative AssessmentMethodology to Overcome Technical ChallengesInitial Experiments on Healthy SubjectValidation Experiments on CP SubjectsFuture WorkConclusion22Validation Experiments on Children with CP

Experiment Setup4 CP Subjects Wearing AFOsVicon markers and TEMPO instrumented at the same timeOn Ground Walking for Several TrialsWithin the range of the Vicon cameras About 5 meters each trial

Unexpected ChallengesValidation ChallengeWalking aid devices block the line of sight A few cycles not easy for CP subjects to get on treadmillMounting Calibration ChallengeCP subject with crouch gait has difficulty to stand straight and still Need of assistance from the research staff for holding the subjects shanks

2323Ankle Joint Angle Validation24

24Ankle Joint Angle Validation (contd.)25

Ankle Joint Angle Range Validation26Shank Angular Velocity Validation

2727Enabling Study OutcomesSufficient Accuracy for Key Gait Parameters ExtractionValidated against Vicon for Children with CP

28Validated!28Future WorkFuture Plan for CP Subject StudyFabricate AFOs and non-AFOswith compartments sized for molding TEMPOInstruct Children with CPwear AFO/non-AFO as they typically docharge the device and upload data to the remote siteFuture Plan for Technology UpdatesMolding Inertial Sensors into the AFOsData Streaming UnnecessaryData caching for opportunistic offloading Ensuring battery lifeMore Analysis Enabled to Assess AFO EfficacyGait SpeedPhase Portrait -- Gait Stability and Complexity 2929Phase Portrait Comparison Healthy Subject

30Phase Portrait Comparison CP subject

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AFO ManufacturersMedicalResearchersPhysiciansCaregiversConclusionValidation of MethodologyEnabled Continuous Longitudinal Study Improve Patient OutcomesTailor AFO for each individual

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