the isb model for the upper extremity dirkjan veeger carolien van andel jaap harlaar esmac seminar...
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The ISB model for the Upper Extremity
DirkJan Veeger
Carolien van Andel
Jaap Harlaar
ESMAC Seminar “Movement Analysis of the Upper Extremity”
www.internationalshouldergroup.org
Contents
• Introduction– 3D motion description basics– Segment motion - joint motion
• The ISB model– Choices– Procedure– intricacies
• Issues – Euler angles and joint rotation– Reference values– compatibility
Introduction: 3D kinematics basics
• The full description of an object in 3D space requires the coordinates of three points on that object
• Follow the plane. The path of the nose, or the wing tips do not fully describe the plane’s motion..
• One needs at least three pointson the plane to quantitativelydescribe what it does.
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
Introduction: 3D kinematics basics
• Orientation definition of a segment requires three markers
• These three markers describe a plane
• In motion analysis these points can be landmarks or technical markers
TS
AI
AA
Introduction: 3D kinematics basics
• From x-y-z global coordinates markers markers we can construct a local coordinate system (or: frame)
• Frame describes its orientation and position (= pose) in global space
TS
AI
AA
Yg
Xg
Zg
• Five steps to define a local frame
– step 1: define the first axis– Step 2: define a support axis
to define the plane orientation
– Step 3: define a second axis perpendicular to the plane
– Step 4: orthogonize your system: calculate the axis in the plane perpendicular to the first two
– Step 5: construct the orientation matrix
TS
AI
AA z
€
z u =AA − TS
AA − TS
• Five steps to define a local frame
– step 1: define the first axis– Step 2: define a support axis
to define the plane orientation
– Step 3: define a second axis perpendicular to the plane
– Step 4: orthogonize your system: calculate the axis in the plane perpendicular to the first two
– Step 5: construct the orientation matrix
TS
AI
AA Z
Ytemp
€
z u =AA − TS
AA − TS
y temp =AA − AI
AA − AI
• Five steps to define a local frame
– step 1: define the first axis– Step 2: define a support axis
to define the plane orientation
– Step 3: define a second axis perpendicular to the plane
– Step 4: orthogonize your system: calculate the axis in the plane perpendicular to the first two
– Step 5: construct the orientation matrix
TS
AI
AA
Xs
Zs
Ytemp
€
z u =AA − TS
AA − TS
y temp =AA − AI
AA − AI
x = y temp × z u, x u =x
x
• Five steps to define a local frame
– step 1: define the first axis– Step 2: define a support axis
to define the plane orientation
– Step 3: define a second axis perpendicular to the plane
– Step 4: orthogonize your system: calculate the axis in the plane perpendicular to the first two
– Step 5: construct the orientation matrix
TS
AI
AA
Ys
Xs
Zs
€
z u =AA − TS
AA − TS
y temp =AA − AI
AA − AI
x = y temp × z u, x u =x
x
y = z × x , y u =y
y
• Five steps to define a local frame
– step 1: define the first axis– Step 2: define a support axis
to define the plane orientation
– Step 3: define a second axis perpendicular to the plane
– Step 4: orthogonize your system: calculate the axis in the plane perpendicular to the first two
– Step 5: construct the orientation matrix = all three axes / direction vectors
TS
AI
AA
Ys
Xs
Zs
€
z u =AA − TS
AA − TS
y temp =AA − AI
AA − AI
x = y temp × z u, x u =x
x
y = z × x , y u =y
y
R = x u y u z u[ ]
• The resulting 3x3 matrix describes the orientation of a segment in the global system
• The matrix contains the three direction vectors,
• Each direction vector defines the angle of that axis with the three axes of the global coordinate system
TS
AI
AA
€
Rscapula =
cos(x, X) cos(y, X) cos(z,X)
cos(x,Y ) cos(y,Y ) cos(z,Y )
cos(x,Z) cos(y,Z) cos(z,Z)
⎡
⎣
⎢ ⎢ ⎢
⎤
⎦
⎥ ⎥ ⎥
P scapula = AAglobal + Rscapula ⋅ x local =
with
det(Rscapula ) =1
AAglobal = Origin scapula frame
• The segment orientations can also be expressed relative to each other :– Joint orientation matrix
€
Relbow = RhumerusT ∗R forearm
c 0 s0 1 0-s 0 c
c -s 0s c 00 0 1
1 0 00 c -s0 s c
Decomposition of a matrix:vector rotation basics
• Rotation matrices can be used to rotate a point to any given position in a plane over a specified angle: (Rz), (Ry) or (Rx)
• The transpose of these matrices rotate the axes of a coordinate system towards a given vector (which is a rotation - for Rz etc.)
• The segment-, or joint orientation matrix can be seen as built up from three rotations– This can be any order of rotations: x-y-z, y-z-y etc.
• Decomposition is the extraction of these three rotations from the orientation matrix– What order is a matter of choice, but:– Each different order yields different results
Decomposition of a matrix:vector rotation basics
Decomposition of a joint orientation matrix
• Choose meaningful axes to rotate around...– Flexion-extension - ab/adduction - axial rotation– Plane of elevation - elevation - axial rotation– ??
• Standard protocol necessary!
QuickTime™ en eenTIFF (ongecomprimeerd)-decompressor
zijn vereist om deze afbeelding weer te geven.
[30,120,45]
180
0
90
180
90
30
60
30 60 120 150
120
150
North Pole
South Pole
45
€
let : Rx =
1 0 0
0 cosα −sinα
0 sinα cosα
⎡
⎣
⎢ ⎢ ⎢
⎤
⎦
⎥ ⎥ ⎥,Ry =
cosβ 0 sinβ
0 1 0
−sinβ 0 cosβ
⎡
⎣
⎢ ⎢ ⎢
⎤
⎦
⎥ ⎥ ⎥,Rz =
cosγ −sinγ 0
sinγ cosγ 0
0 0 1
⎡
⎣
⎢ ⎢ ⎢
⎤
⎦
⎥ ⎥ ⎥
Rzxy =
r11 r12 r13
r21 r22 r23
r31 r32 r33
⎡
⎣
⎢ ⎢ ⎢
⎤
⎦
⎥ ⎥ ⎥= Rz ⋅ I( ) ⋅Rx( ) ⋅Ry( ) = Rzg ⋅Rxl ⋅Ryl
=
cosγ cosβ − sinγ sinα sinβ −sinγ cosα cosγ sinβ + sinγ sinα cosβ
sinγ cosβ + cosγ sinα sinβ cosγ cosα sinγ sinβ − cosγ sinα cosβ
−cosα sinβ sinα cosα cosβ
⎡
⎣
⎢ ⎢ ⎢
⎤
⎦
⎥ ⎥ ⎥
Decomposition example (see Capozzo, 2005)
This value in the orientation matrix can be used to calculate , the
rotation around the x-axis.
These values can be used to calculate
, the rotation around the z-axis
• Definition of local coordinate systems– Landmarks – Axis directions
• Definition of decomposition orders– Full text: see Wu et al, 2005
• Now: example humerus– Landmarks– Decomposition order
ISB Upper extremity model: choices
• ISB choice: local frames based on anatomical landmarks
ISB Upper extremity model: procedure
Procedure sensitive to landmark estimation errors
– Local humerus frame defined on three landmarks:
• EM, EL and GH
– GH has to be estimated• From kinematics (Helical axes or sphere
fit)• based on regression (Meskers et al. 1998)
• Alternative proximal marker in fixed position
– Long axis defined first, followed by axis perpendicular to plane
• Alternative procedure:– Use GH, EL, EM and forarm
markers
• Forearm used for definition of plane– Dependent on elbow angle: ISB
suggests 90° flexion and 90° pronation as reference position
• Long axis defined first, followed by axis perpendicular to plane
ISB Upper extremity model: procedure
[30,120,45]
180
0
90
180
90
30
60
30 60 120 150
120
150
North Pole
South Pole
45
• Proposed decomposition order:– Plane of elevation– Elevation– Axial rotation
• Gimbal lock when Plane of elevation is 0°, or 180°
• Applicable for thoracohumeral and glenohumeral motion
• “Comply or Explain”
ISB Upper extremity model: procedure
• Landmarks on the scapula can not directly be measured!
ISB Upper extremity model: intricacies
QuickTime™ and aYUV420 codec decompressorare needed to see this picture.
• Landmarks on the scapula can not directly be measured!– Use scapula locator
• (quasi static)
– Use markers on acromion• Reliability above 100° elevation?
– Estimate from thorax and arm orientation
• Tricky in patients..
ISB Upper extremity model: intricacies
Scapula locator
• Not unique to the ISB UX approach, but:– Model assumes that local coordinate systems are
aligned: no reference position• In full extension, the long axes of the arm might not be
exactly aligned: leads to variations in the second rotation.• These variations are NOT elbow abduction.... Or change in
carrying angle
ISB Upper extremity model: intricacies
• Not unique to the ISB UX approach, but:
– Upper extremities have large axial rotations and:• Landmarks / sensors sensitive to soft tissue deformation in axial
rotation• Local coordinate definition very sensitive to relative positions of
landmarks during calibration (= definition of local coordinate systems)
– Advice: always measure a separate reference position, preferably 0° arm elevation, 90° arm axial rotation, 90° flexion and 90° pronation
ISB Upper extremity model: intricacies
– ISB model is based on anatomical frames and not functional axes
– Euler angles and joint rotations are not the same:
• Elbow motion = forearm segment relative to arm segment
• Decomposition yields three Euler angles, but NOT actual elbow joint motion!
• The second rotation: ab-adduction is due to ‘mis’alignment, but:
– The Euler angles DO describe relative segment motion
• For ‘real’ joint motion (flexion, pro-supination), use other axes, or fit a kinematic model
ISB Upper extremity model: issuesy-axis arm
y-axis forearm
z-axis arm
– Compatibility: dependent on all steps of the procedure
• Landmark choice and definition• Definition order of local segment axes• Decomposition order of orientation matrix
– Comply or Explain!
ISB Upper extremity model: issues
Summary
• The ISB protocol is based on anatomical frames– Other options possible, but not interchangeable
• The ISB protocol gives a prescribed definition order for local frame axes
– Other options possible, but not interchangeable
• The ISB protocol defines the decomposition order for segment- and joint orientation matrices / frames
– Other options possible, but not interchangeable
• ISB protocol is not perfect, but still seems to be the basis for UE motion analyses
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