Introduction to the

Conventional Gait Model

Richard Baker

Professor of Clinical Gait Analysis

Blog: wwRichard.net

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Conventional Gait Model

Newington, Davis,Gage

Helen Hayes, Kadaba

Vicon Clinical Manager (VCM), Plugin Gait

Conventional gait model (Visual 3d)

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Conventional Gait Model

By far the most widely used and best

understood model in clinical gait analysis.

Widely used in more general applications.

Better validated than any other model.

Better standardised than any other model.

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What is a model4

Triangles5

LineTriangle = + point

Triangles6

Defines a plane

Understanding the model7

Where are the lines and points that define the triangles?

Understanding the model

• Anatomical segment definition

• Theory of marker placement

• Placing markers on the ideal person

• Placing markers on less ideal people.

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Anatomical segment

definition

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Femur10

Principal axis From hip joint centre to knee joint centre

Reference pointLateral epicondyle

Tibia11

Principal axis From knee joint centre to ankle joint centre

Reference pointLateral malleolus

Pelvis12

Principal axis From one ASIS to the other

Reference pointMid point of PSIS

Foot13

Principal axis Along long axis of foot

Foot14

Principal axis Along long axis of foot

Theory of marker placement

(Ideal person)

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Marker placement

• The system only sees the middle of the

marker (not the baseplate)

• Use landmarks as a guide and try and

visualise the lines and planes

• Always place markers on skin

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Hiearchical model17

Pelvis18

Principal axis From one ASIS to the other

Reference pointMid point of PSIS

Right ASIS (Anterior superior iliac spine)

Left ASIS

Pelvis19

Principal axis From one ASIS to the other

Reference pointMid point of PSIS

Left PSIS (Posterior superior

iliac spine)

Right PSIS

Pelvis20

Principal axis From one ASIS to the other

Reference pointMid point of PSIS

Marker centres are a marker radius in front of ASIS

Need to tell software what the marker diameter is

Femur21

Principal axis From hip joint centre to knee joint centre

Reference pointLateral epicondyle

Lateral epicondyle

Femur22

Femoral head (femur) and cetnre of acetabulum (pelvis) are in same place.

Femur23

Medio-lateral distance is a proportion of ASIS width

If InterASISDistance is measured and entered PiG will use this.

If not PiG will take measured distance between ASIS

Femur24

Anterior-posterio distance

If AsisTrocDist is entered then PiG will calculate a distance based on this and leg length.

If not the distance is calculated as a function of leg length only

AsisTrocDist25

Distance in anterior-posterior direction (not measured round body)

Femur26

Proximal-distal distance

If AsisTrocDist is entered then PiG will calculate a distance based on this and leg length.

If not the distance is calculated as a function of leg length only

Femur27

Thigh wand determines the coronal plane of the femur

Femur28

50% to 70% of distance from hip to knee

AsisTrocDist29

Distance in anterior-posterior direction (not measured round body)

AsisTrocDist30

Distance in anterior-posterior direction (not measured round body)

Tibia31

Principal axis From knee joint centre to ankle joint centre

Reference pointLateral malleolus

Lateral malleolus

Tibia32

Knee joint centre assumed fixed in both femur and tibia

Tibia33

Knee joint centre is half knee width in from lateral epicondyle

Tibia34

Shank wand determines the coronal plane of the tibia

50% to 70% of distance from knee to ankle

Foot35

Principal axis Along long axis of foot

Foot36

Foot37

Knee joint centre is half knee width in from lateral epicondyle

Foot38

On second ray at level of “bump” on 1st cuneiform-metatarsal joint

A more distal marker may give erroneous dorsiflexion if foot deforms

Foot39

Foot rotation

offset

Plantarflexion offset

Need to define green line in static test

Foot40

Foot rotation

offset

Plantarflexion offset

Line from heel to forefoot markers defines long axis of foot in horixontal plane

Foot41

Foot rotation

offset

Plantarflexion offset

Line from heel to forefoot markers defines long axis of in sagittal plane

(or check foot flat box)

Foot42

If foot not flat on the ground heel marker must be same distance from plantar surface as forefoot marker

Plantarflexion offset

Placing markers on less

ideal people

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Pelvis44

Must enter AsisTrocDist

Must still palpate landmarks

Pelvis45

Keep markers symmetrical

Pelvis46

If you move markers out and forwards you must enter interAsis distance

Thanks for listening

Richard Baker

Professor of Clinical Gait Analysis

Blog: wwRichard.net

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