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
1
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
16
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
3131
AFO
ManufacturersMedicalResearchersPhysiciansCaregiversConclusionValidation
of MethodologyEnabled Continuous Longitudinal Study Improve Patient
OutcomesTailor AFO for each individual
32NetworkEMRServer32 Thanks!33
33