observational gait analysis nerrolyn ford phd. the observational gait analysis process...

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