Mobile Bearing TKA - University of...
Transcript of Mobile Bearing TKA - University of...
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Mobile Bearing TKA
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Knee JointComplex motion
•flexion/extension•sliding•rolling•endo/exorotation
Large joint loads•4 x body weight
Cartilage degeneration ⇒ osteoarthritis
femur
patella
tibia
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femoralcomponent
tibialcomponent
poly
Total Knee Replacement•Resurface joint ends
•metal and plastic•Accommodate complexmotion
Fixed bearing•Single contact surface•Round on flat•High stresses ⇒ wear/failure•Balance conformity/constraint
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Mobile Bearing Total Knees•↑ conformity, ↓ constraint•Two contact surfaces•Abnormal kinematics•Limited bearing motion
(Nilsson et al., 1991; Stiehl et al., 1997; Hartford et al., 2001)
•High conforming fixed bearing
Understanding mobility important to success
PFC SigmaRotating Platform TKA
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TKA Mobile Bearing Designs
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LCS (DePuy)
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Hypothesis
•Friction at the “mobile” interface of a rotating platform total knee produces sufficient counter-torque to interfere with endo/exorotation.
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LCS PS (DePuy)Femoral Component
•PC substituting
Tibial Tray• rotating platform II
Polyethylene Insert• 10.0 mm thickness
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Finite Element MeshModel Geometry
• IGES
Metal Components•ECoCr >> Epoly• rigid Bezier surface•3-noded triangular
Polyethylene Insert• 8-noded brick
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Polyethylene Material PropertiesE(σ) = 634.92 – 12.31σ – 3.61σ2 + 0.199σ3 – 0.00283σ4
0
10
20
30
40
50
60
0 0.2 0.4 0.6Strain (mm/mm)
Stre
ss (M
Pa)
Nonlinear model(Cripton, 1993)634.92
ν = 0.45
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Dual SurfaceInteractions“Bearing” Interface
•FC/PE insert
“Mobile” Interface•TT/PE insert
Friction•µ = 0.089
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Constraints/FreedomsFemoral Component
• free translation• free varus/valgusrotation
Tibial Tray• fixed translation•prescribed internalrotation
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Loading Conditions
Variables Examined• resisting torque • contact area•contact stress • relative rotation
LoadAllocation
Axial Load(BW)
FlexionAngle (°)
InternalRotation (°)
50-50 1, 2, 3, 4 0 1060-40 1, 2, 3, 4 0 10
50-50 10,15,2030,60,90 10
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Step Procedure1: TT/PE into contact
2: FC/PE into contact
3: 50 N load
4: PE freed
5: FC freed in translationand V/V rotation
6: Physiological load
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Testing FixtureFemoral Component
•axial/torsional load•endo/exorotation• flexion
Tibial Tray•M/L and A/P•V/V
Condylar Load•equal•medially biased
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0° Flexion
0
1
2
3
4
5
6
7
0 2 4 6 8 10Tibial Tray Rotation (deg)
Res
istin
g To
rque
(N-m
) 4 BW
3 BW
2 BW
1 BW
50-5060-40
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0°
0
1
2
3
4
5
6
7
0 1 2 3 4x Body Weight
Res
istin
g To
rque
(N-m
)
50-5060-40
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0° Flexion
0
1
2
3
4
5
6
7
1 2 3 4x Body Weight
Res
istin
g To
rque
(N-m
)
50-50 FEM50-50 EXP60-40 FEM60-40 EXP
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50-50, 1 BW
0.0
0.5
1.0
1.5
2.0
0 15 30 45 60 75 90Flexion Angle (deg)
Torq
ue (N
-m)
FEMEXP
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50-50, 0° Flexion
4 BW
1 BW
No rotation 10º rotation
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50-50, 0° Flexion
A
P
ML
2 BW
28 mm
Stress Distribution•peripheral edge loading• long moment arm•FE/Exp match well
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0° Flexion
0
200
400
600
800
1000
1200
0 1 2 3 4x Body Weight
Con
tact
Are
a (m
m2 )
'mobile' interface
'bearing' interface
50-5060-4050-5060-40
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50-50, 1 BW
0
100
200
300
400
500
600
0 15 30 45 60 75 90Flexion Angle (deg)
Con
tact
Are
a (m
m2 )
"bearing" interface
"mobile" interface
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50-50, 1BW
0.0
0.5
1.0
1.5
2.0
0 15 30 45 60 75 90Flexion Angle (deg)
Rel
ativ
e R
otat
ion
(deg
)
FEMEXP
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FE vs Experimental Agreement
•Resisting torque• load allocation•axial load• flexion angle
•Contact stress distribution•peripheral edge loading
•Relative rotation
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Summary
•50-50 and 60-40 same•Resisting torque ∝ axial load•20° flexion ⇒ FC radii transition
• less congruent•↓ contact area•↑ relative rotation
•Peripheral edge loading• large moment arm
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Peak Torque•Present data: 5.98 ± 0.19 N-m•Taylor et al., 1998: 6-8 N-m
Design Improvements?•↓ peripheral stresses•↓ resisting torque
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Loading Conditions•50-50 or 60-40•1, 2, 3, or 4 BW (1 BW = 686.5 N)•0, 15, 20, 30, 60, 90° flexion• internally rotated 10°•elastic ⇒ 4 BW, 50-50, 0° flexion
Variables Examined• resisting torque•contact stress•contact area• relative rotation
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KinematicsFlexion
•60° walking (Lafortune et al., 1992 )• 90° stair ascent/decent (Andriacchi et al., 1980)
Internal/External Rotation•12° walking (Kettelkamp et al., 1970)
Posterior Translation•7 mm walking (Dennis et al., 2001)• 20 mm high flexion (Dennis et al., 2001)
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KineticsAxial Load
•4 BW walking (Morrison, 1970)• 5 BW stair ascent/decent (Morrison, 1969)•Medially biased (Morrison, 1970)
Internal/External Torque•8 Nm walking (Li et al., 1993)
ArthritisCartilage degeneration ⇒ Pain ⇒ TKR
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PurposeStudy the mobility and contact mechanics of rotating platform TKRs under functional loading conditions
MethodMobility ⇒ internal/external torque, rotationContact Mechanics ⇒ contact stress, areaParametric Evaluation
•physical experiments• finite element model
Walking Cycle
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LCS Std (DePuy)Femoral Component
•PC sacrificing•CoCr
Tibial Tray• rotating platform•CoCr
Polyethylene Insert• 6.0 mm thickness
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LCS PS (DePuy)Femoral Component
•PC substituting
Tibial Tray• rotating platform II
Polyethylene Insert• 6.0 mm thickness
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Loading Conditions•Axial load 1, 2, 3, 4 BW (1 BW=687 N)•Load allocation 50-50 or 60-40•Flexion angle 0, 15, 30, 45, 60, 90°•Axial rotation ±10°•Lubrication bovine serum
Variables Examined•Resisting torque
•static/dynamic• Insert rotation lag•Contact distribution (Fuji)
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Finite Element ModelModel Geometry
• IGES → PATRAN
Metal Components•ECoCr >> Epoly• rigid surface•3-noded triangular
Polyethylene Insert• nonlinear solid•8-noded brick
femoralcomponent
tibialtray
polyinsert
LCS Std
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LCS PS
FE AnalysisABAQUS
•3D•Nonlinear
•Materially•Geometrically
•Large displacement•Multi-contact
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Dual SurfaceInteractions•Bearing interface•Mobile interface•Friction, µ = 0.089
Constraints/Freedoms•Same DOF as testingfixture
•PE free to move
“bearing”
“mobile”
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Loading Conditions•Axial load 1, 2, 3, 4 BW (1 BW=687 N)•Load allocation 50-50 or 60-40•Flexion angle 0, 15, 30, 45, 60, 90°•Axial rotation ±10°•Friction µ = 0.089
Variables Examined•Resisting torque • Contact stress• Insert rotation lag • Contact area
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Full Walking Cycle Simulation• ISO 14243-1• Input waveforms
•axial load (medially biased)•axial torque•A/P forces• flexion angle
•Soft tissue constraints•A/P•axial rotation
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0
500
1000
1500
2000
2500
3000
0 20 40 60 80 100Walking Cycle (%)
Axi
al L
oad
(N)
0
10
20
30
40
50
60
0 20 40 60 80 100Walking Cycle (%)
Flex
ion
Ang
le (°
)
-2-101234567
0 20 40 60 80 100
Walking Cycle (%)
Axi
al T
orqu
e (N
-m) internal (+)
external (-) -300-250-200-150-100
-500
50100150
0 20 40 60 80 100
Walking Cycle (%)
A/P
For
ce (N
)
anterior (+)
posterior (-)
ISO 14243-1
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LCS Std vs PS - 50-50, 0° Flexion
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LCS Std vs PS - 50-50, 0° Flexion
0
2
4
6
8
10
0 1 2 3 4x Body Weight
Res
istin
g To
rque
(Nm
)
LCS StdLCS PSStaticDynamic
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50-50 vs 60-40 - 0° Flexion
0
2
4
6
8
10
1 2 3 4x Body Weight
Res
istin
g To
rque
(Nm
)50-5060-40
PS Exp StaticPS Exp DynamicPS FEM DynamicStd FEM Dynamic
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Exp vs FEM - 0° Flexion
0
2
4
6
8
10
1 2 3 4x Body Weight
Res
istin
g To
rque
(Nm
)ExperimentalFEM
Std 50-50PS 50-50PS 60-40
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LCS Standard - 3 BW, 50-50
0123456789
10
0 15 30 45 60 75 90Flexion Angle (°)
Res
istin
g To
rque
(Nm
)
Exp Static
Exp Dynamic
FEM Dynamic
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LCS Standard
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LCS PS - 50-50, 0° Flexion
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50-50, 0° Flexion
0
200
400
600
800
1000
1200
1400
0 1 2 3 4x Body Weight
Con
tact
Are
a (m
m2 )
LCS StdLCS PS
mobile interface
bearing interface
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LCS Standard - 50-50, 3 BW
0
200
400
600
800
1000
1200
1400
0 15 30 45 60 75 90Flexion Angle (°)
Con
tact
Are
a (m
m2 )
bearing interface
mobile interface
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Lag vs Flexion Angle - 3 BW, 50-50
0.0
1.0
2.0
3.0
4.0
0 15 30 45 60 90Flexion Angle (°)
Inse
rt R
otat
ion
Lag
(°)
LCS StdLCS PS
Exp StaticExp DynamicFEM Dynamic
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LCS Standard
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-2
-1
0
1
2
3
4
5
6
0 20 40 60 80 100
% Walking Cycle
Axi
al R
otat
ion
(°)
endorotation (+)
exorotation (-)
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Finite Element Model Validation|
•Resisting torque•axial load• load allocation• flexion angle
• Insert rotation lag•Contact stress distributions
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Peak Torque•LCS Standard: 9.47 N-m (static)
5.51 N-m (dynamic)•Taylor et al., 1998: 6-8 N-m
Internal/External Rotation•LCS Standard: 6°•Normal knee: 12° (Kettelkamp et al., 1970)
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Summary
•Resisting torque ∝ axial load•50-50 and 60-40 same•Mobile area > bearing area•25-30° flexion ⇒ FC radii transition
• less congruent, ↓ contact area•↑ insert rotation lag
• Insert rotation lag small•Contact stresses < 7 MPa
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Comparison Std PSEdge loading •Contact stresses •Contact area
bearing •mobile •
Insert rotation lag •Resisting torque
static •dynamic •
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mobile bearing
Backside wear•mobile bearing• fixed bearing
Evaluate other designs•capture mechanisms•PC substituting posts
Improve mobility•parametric designchanges
fixed bearing
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LCS PS - 50-50, 0° Flexion
4 BW
1 BW
No rotation 10º rotation
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Standard PS
FEA Full Gait Cycle Comparisons
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Flanges
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Insert Footprints
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0
500
1000
1500
2000
2500
3000
0 20 40 60 80 100Walking Cycle (%)
Axi
al L
oad
(N)
0
10
20
30
40
50
60
0 20 40 60 80 100Walking Cycle (%)
Flex
ion
Ang
le (°
)
-2-101234567
0 20 40 60 80 100
Walking Cycle (%)
Axi
al T
orqu
e (N
-m) internal (+)
external (-) -300-250-200-150-100
-500
50100150
0 20 40 60 80 100
Walking Cycle (%)
A/P
For
ce (N
)
anterior (+)
posterior (-)
ISO 14243-1
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-2
-1
0
1
2
3
4
5
0 20 40 60 80 100% Walking Cycle
Axia
l Rot
atio
n (d
eg)
StandardPS
external (-)
internal (+)
(a)
Axial Rotation
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Lift-Off
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0.0
0.5
1.0
1.5
2.0
0 20 40 60 80 100% Walking Cycle
Lifto
ff (m
m)
-5
0
5
10
15
20
Rol
lbac
k (m
m)
StandardPS
LiftoffRollback
(b)
Rollback & Lift-Off
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0
5
10
15
20StandardPS
anterior posterior
(a)
medial profile
Bearing Surface Contact Stress
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0
5
10
15
20StandardPS
anterior posterior
(b)
medial profile
Mobile Interface Contact Stress