The document provides an introduction to the conventional gait model, which is the most widely used and best validated model in clinical gait analysis. It describes the anatomical segment definitions used in the model, including defining the principal axes and reference points for the pelvis, femur, tibia, and foot segments. It discusses the theory of marker placement, including placing markers over bony landmarks on an ideal person and techniques for placing markers on less ideal people.

1. Introduction to the
Conventional Gait Model
Richard Baker
Professor of Clinical Gait Analysis
Blog: wwRichard.net
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2. Conventional Gait Model
Newington, Davis,Gage
Helen Hayes, Kadaba
Vicon Clinical Manager (VCM), Plugin Gait
Conventional gait model (Visual 3d)
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3. 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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4. What is a model
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5. Triangles
5
LineTriangle = + point

6. Triangles
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Defines a plane

7. Understanding the model
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Where are the lines and
points that define the
triangles?

8. 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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9. Anatomical segment
definition
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10. Femur
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Principal axis
From hip joint centre to
knee joint centre
Reference point
Lateral epicondyle

11. Tibia
11
Principal axis
From knee joint centre
to ankle joint centre
Reference point
Lateral malleolus

12. Pelvis
12
Principal axis
From one ASIS to
the other
Reference point
Mid point of PSIS

13. Foot
13
Principal axis
Along long axis of foot

14. Foot
14
Principal axis
Along long axis of foot

15. Theory of marker placement
(Ideal person)
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16. 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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17. Hiearchical model
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18. Pelvis
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Principal axis
From one ASIS to
the other
Reference point
Mid point of PSIS
Right ASIS
(Anterior superior iliac spine)
Left ASIS

19. Pelvis
19
Principal axis
From one ASIS to
the other
Reference point
Mid point of PSIS
Left PSIS
(Posterior superior
iliac spine)
Right PSIS

20. Pelvis
20
Principal axis
From one ASIS to
the other
Reference point
Mid point of PSIS
Marker centres are a marker
radius in front of ASIS
Need to tell software what the
marker diameter is

21. Femur
21
Principal axis
From hip joint centre to
knee joint centre
Reference point
Lateral epicondyle
Lateral epicondyle

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

23. Femur
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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

24. Femur
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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

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

26. Femur
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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

27. Femur
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Thigh wand determines the coronal plane of the femur

28. Femur
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50% to 70% of distance
from hip to knee

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

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

31. Tibia
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Principal axis
From knee joint centre
to ankle joint centre
Reference point
Lateral malleolus
Lateral malleolus

32. Tibia
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Knee joint centre assumed fixed in both femur and tibia

33. Tibia
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Knee joint centre is half knee width in from lateral epicondyle

34. Tibia
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Shank wand determines the coronal plane of the tibia
50% to 70% of
distance from
knee to ankle

35. Foot
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Principal axis
Along long axis of foot

36. Foot
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37. Foot
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Knee joint centre is half knee width in from lateral epicondyle

38. Foot
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On second ray at level of “bump” on 1st cuneiform-metatarsal joint
A more distal marker may give erroneous dorsiflexion if foot deforms

39. Foot
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Foot
rotation
offset
Plantarflexion
offset
Need to define green line in static test

40. Foot
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Foot
rotation
offset
Plantarflexion
offset
Line from heel to forefoot markers defines long axis of foot in horixontal plane

41. Foot
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Foot
rotation
offset
Plantarflexion
offset
Line from heel to forefoot markers defines long axis of in sagittal plane
(or check foot flat box)

42. Foot
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If foot not flat on the ground heel marker must be same distance
from plantar surface as forefoot marker
Plantarflexion
offset

43. Placing markers on less
ideal people
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44. Pelvis
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Must enter AsisTrocDist
Must still palpate
landmarks

45. Pelvis
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Keep markers symmetrical

46. Pelvis
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If you move markers out and forwards you must enter interAsis distance

47. Thigh markers
Visualising the knee joint axis
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48. 48

49. 49

50. 50

51. 51

52. 52

53. 53
Note that the thigh wand is not necessarily perpendicular to the floor
– it is the marker position that is important
Fine adjustment is
almost impossible
with skin markres

54. Hip Flexion
70
-20
Flex
Ext
deg
Knee Flexion
75
-15
Flex
Ext
deg
Dorsiflexion
30
-30
Dors
Plan
deg
Hip Adduction
30
-30
Add
Abd
deg
Knee Adduction
30
-30
Var
Val
deg
Foot Progression
30
-30
Int
Ext
deg
Hip Rotation
30
-30
Int
Ext
deg
Knee Rotation
30
-30
Int
Ext
deg
Ankle Rotation
30
-30
Int
Ext
deg
Misplaced thigh marker (too anterior)
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55. 55

56. Misplaced thigh marker
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Hip Flexion
70
-20
Flex
Ext
deg
Knee Flexion
75
-15
Flex
Ext
deg
Dorsiflexion
30
-30
Dors
Plan
deg
Hip Adduction
30
-30
Add
Abd
deg
Knee Adduction
30
-30
Var
Val
deg
Foot Progression
30
-30
Int
Ext
deg
Hip Rotation
30
-30
Int
Ext
deg
Knee Rotation
30
-30
Int
Ext
deg
Ankle Rotation
30
-30
Int
Ext
deg

57. Medial malleolus marker
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58. Thanks for listening
Richard Baker
Professor of Clinical Gait Analysis
Blog: wwRichard.net
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