observational gait analysis nerrolyn ford phd. the observational gait analysis process...
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Observational Gait Analysis
Nerrolyn Ford PhD
• The observational gait analysis process
• Reliability/Validity
• What is done in practice?• Visual search strategies
• Decision making strategies
Issues for discussion
Selection of Cues to observe
Evaluation of Cues
Interpretation of findings
The Observational Gait
Analysis process
Selection of Cues to observe
Evaluation of Cues
Interpretation of findings
Plane:
Coronal
Sagittal
Parameter
Temporal
Spatial
Kinematic
Region:
Feet KneesHipsTrunkShoulderArmsHandsHead
Selection of Cues to observe
Evaluation of Cues
Interpretation of findings
Theoretical/biomechanical knowledge
Internalizedmodel of
“normal walking”
Working environment/ Interaction with colleagues
Experience/exposure to similar cases
Selection of Cues to observe
Evaluation of Cues
Interpretation of findings
Normal
Abnormal
Decision to intervene
Decision about success of treatment
Decision not to intervene
Decision to attend to different cues
Observational gait analysis reliability
Study Entityobserved
Obsever Reliability estimates
Goodkin andDiller (1973)
Hemiplegicgait
Physiotherapists
(Live viewing)
specific deviations = 82%
Preferred treatment = 28%
Saleh andMurdoch(1985)
Amputee gait Surgeons, Physicians,Physiotherapists,Prosthetists
(Live viewing)
Observed/Predicted deviations = 22%
Krebs et al.(1985)
Gait of childrenfitted withbilateralKAFO’s
Physiotherapists
(Video taped viewing)
Within rater r = 0.6
Between rater r < 0.6
Keenan andBach (1996)
Rearfootmotion
Podiatrists
(Video taped viewing)
Between rater k = 0.19Within rater range k = -0.13 to 0.59
Ford et al.(1995)
Amputee gait Prosthetists
(Video taped viewing)
A/P alignment shift k = 0.08M/L alignments shifts k= 0.46
Research Aims
• Investigate and describe the current practice of observational gait analysis from an information processing and visual search perspective
• Develop and test an observational gait analysis training program
Decision making in OGA
• Examine specific methods and cognitive processes used by clinicians performing observational gait analysis.
• Identify sources of error and bias that may compromise OGA reliability and validity
Method (subjects)• 17 clinicians represent different
professional groups– Prosthetics, orthotics, physiotherapy, medicine
• Clinicians evaluated in their own clinical environment while performing a gait related consultation
• Video assisted recall
Method• Prior to performing a clinical consultation
clinicians were fitted with a lightweight head mounted video camera
Recall session• Immediately after performing the consultation
clinicians participated in a recall session
– View video and attempt to verbalise thoughts, feeling and decisions they remember having had at the time of the consultation
– Recall sessions dubbed over a copy of the original tape and transcribed verbatim for coding and analysis
Transcript coding
• Decision type– treatment or diagnostic
• Decision strategy– Hypothetico-deductive, pattern
recognition, exhaustive, multiple branching
• Observational variables– kinematic upper limb– kinematic lower limb– temporospatial
Results (decision strategy)Orthotists Prosthetists Physiotherapists Medical
specialists
Total
Pattern
recognition
32 19 46 22 119
Multiple
branching
3 14 26 7 50
Hypothetico
-deductive
0 3 0 3 6
Exhaustive 0 1 0 0 1
Total 35 37 72 32 176
Results (observational variables)
0
20
40
60
80
100
Pros
thet
ist
Ort
hoti
st
Phys
ioth
erap
ist
Med
ical
spec
iali
st
% to
tal v
aria
bles
Upper extremity,temporospatialand "other"
Lower extremitykinematic
% of OGA spent viewing coronal versus sagittal plane
14.0%
86.0%
0
20
40
60
80
100
Coronal Sagittal
Major findings
• All clinicians tend to use a pattern recognition decision strategy
• Clinicians differ in the types of decisions made
• Clinicians differ in the observational variables they consider
If clinicians differ in the information they consider, do they differ in the information
they visually attend to?
Study aims
• Compare the visual search strategies of expert clinicians, novice clinicians and lay subjects
Testing sessions
• Video taped footage of 10 gait affected and 2 non affected subjects (split screen)
• Identify “major” walking problems
• Eye movements tracked using video based eye tracking system (DBA systems inc.)
Participants
16 expert cliniciansProsthetists, orthotists, physiotherapists,
medical specialist
13 novice clinicians2nd year prosthetics and orthotics
students
5 lay subjectsNo prior experience in gait assessment
Recording of eye movements using video based tracking system
Data analysis procedure
• x-y coordinates of eye position (eye tracker)
• x-y coordinates of major joints, head & trunk (PEAK)
• visual fixation occurs when eye remains within designated region for 0.24 seconds
Data analysis
Visual fixations – Location
• Plane (coronal or sagittal)
• Body region (feet, knees, hips, trunk, shoulders, elbows, hands, head)
– Sequencing
Location of visual fixations (expert/novice/lay)
0
20
40
60
80
100
Expert Novice Lay
% to
tal f
ixat
ions
Sagittal
Coronal
he
ad
hand
s
elbo
ws
shou
lder
s
trun
k
hips
knee
s
feet
% t
otal
fix
atio
ns60
50
40
30
20
10
0
Group
student
expert
lay
Location of visual fixations (expert/novice/lay)
Sequencing of visual fixations
Lay subjects Novice subjects Expert subjects
Important findings
• Coronal plane viewing bias (expert/novice and lay subjects)
• expert clinicians allocate significantly greater proportion of fixations to the trunk and upper body
• eye movement transitions most likely to occur from superior to an inferior body region
• Novice clinicians more likely to make eye movement transitions between anatomically distant body regions
Can visual search strategies be taught to novice clinicians?
Traditional model of teaching observational gait analysis
• Knowledge/cue based learning
• Specific body regions (Segment by segment)
• Theoretical training rather than experience based training
Perceptual training
• Novice task performers will eventually gravitate towards pattern recognition decision strategies
• Training more efficient if it complements pattern recognition strategies from the outset
(Kirlik et al., 1996)
• Reduces cognitive load
• Less sensitive to situations of high stress, time pressures
• More likely to be retained over a period of time
(Rogers et al., 1997)
Perceptual training
Aim
Investigate effects of perceptual training on visual search strategies
of novice clinicians
Method
S y stem atic eva lua tionfee t - knees - h ip s - trunk - head
C ue based lea rn ing6 s tuden ts
P a tho log ica l cond itionsexpec ted gait dev ia tions
P a tho logy based lea rn ing7 s tuden ts
13 P & O s tuden ts2nd y ea r o f s tudy
Testing sessions1 - pre-training2 - post training
3 - five months post training
Results - Coronal versus sagittal plane viewing
0
25
50
75
100
1 2 3 expertTesting occasion
%SagittalCoronal
* * * *
Distribution of fixations pre v/s post training
Pathology CueFeet
Knees
Hips
Trunk
Shoulders
Elbows
Hands
Head
Distribution of fixations pre v/s 5-months post training
Pathology CueFeet
Knees
Hips
Trunk
Shoulders
Elbows
Hands
Head
Sequencing of visual fixationsPathology-based learning group
Pre-training Post-training 5 months post
Sequencing of visual fixationsCue-based learning group
Pre-training Post-training 5 months post
• Both training groups significantly increased the proportion of fixations directed at the upper body
• Cue groups were less rapid to respond to training, did not adopt the search strategy emphasised throughout training.
Discussion
How can we improve our OGA skills
• Recognize errors and biases
• Observer training
• Optimize viewing conditions
• Collect appropriate patient information (narrow the search)
• Identify visual cues that can be observed in a valid and reliable manner
• Nature and number of visual cues that must be observed in order to make a valid and reliable decision