Upload
lee-parsons
View
217
Download
0
Embed Size (px)
DESCRIPTION
VMO Training VMO resists lateral force and lateral tilt momentVMO resists lateral force and lateral tilt moment A weak VMO and delayed VMO activation can contribute to patellofemoral painA weak VMO and delayed VMO activation can contribute to patellofemoral pain Physical therapy regimens commonly emphasize training the VMOPhysical therapy regimens commonly emphasize training the VMO Stoller et al. Interactive Knee - Radiology ©1999 Primal Pictures Ltd.
Citation preview
Patient-Specific Analysis of the Patient-Specific Analysis of the Influence of VMO Training on Influence of VMO Training on
Patellofemoral Forces and Patellofemoral Forces and PressuresPressures
John J. Elias, PhDSurya P. Rai, MS
David M. Weinstein, MDDavid L. Walden, MD
Medical Education and Research Institute of ColoradoColorado Springs, CO
Patellofemoral PainPatellofemoral Pain• Patellofemoral pain is frequently Patellofemoral pain is frequently
attributed to lateral malalignment attributed to lateral malalignment • Lateral shift and tilt can increase Lateral shift and tilt can increase
pressure applied to lateral cartilagepressure applied to lateral cartilage• Overloading cartilage can lead to Overloading cartilage can lead to
cartilage degradation cartilage degradation and painand pain
VMO TrainingVMO Training
• VMO resists lateral force and VMO resists lateral force and lateral tilt momentlateral tilt moment
• A weak VMO and delayed VMO A weak VMO and delayed VMO activation can contribute to activation can contribute to patellofemoral painpatellofemoral pain
• Physical therapy regimens Physical therapy regimens commonly emphasize training commonly emphasize training the VMOthe VMO
Stoller et al.Interactive Knee - Radiology©1999 Primal Pictures Ltd.
Study GoalsStudy Goals
• Create computational models Create computational models representing patients with representing patients with patellofemoral painpatellofemoral pain
• Characterize how eliminating VMO Characterize how eliminating VMO weakness and delayed VMO weakness and delayed VMO activation influence patellofemoral activation influence patellofemoral force and pressure distributionsforce and pressure distributions
Patient-Specific ModelsPatient-Specific Models• Obtained IRB approvalObtained IRB approval• MRI images of knees at MRI images of knees at
full extension and 45full extension and 45°° [Cohen [Cohen et al., Am J Sports Med 31:87-98]et al., Am J Sports Med 31:87-98]
• Reconstructed bone Reconstructed bone surfaces and cartilagesurfaces and cartilage
• Characterize orientation Characterize orientation of quadriceps muscles of quadriceps muscles and patella tendon and patella tendon [Delp et al. [Delp et al. IEEE Trans Biomed Eng 37: 557-567, IEEE Trans Biomed Eng 37: 557-567, Farahmand et Farahmand et al. J Orthop Res. 16:136-43al. J Orthop Res. 16:136-43]]
Patella Tendon
VMO VL
VML
RF
VI
Patellofemoral KinematicsPatellofemoral Kinematics
• Rotate tibia about distal femurRotate tibia about distal femur• Characterize patellofemoral Characterize patellofemoral
alignment of flexed kneealignment of flexed knee• Maintain patella apex within groove Maintain patella apex within groove
and orientation of lateral facetand orientation of lateral facet• Patella flexion Patella flexion
proportional to proportional to tibiofemoral flexiontibiofemoral flexion
Patellofemoral CartilagePatellofemoral Cartilage• Identify cartilage lesions based on Identify cartilage lesions based on
thicknessthickness• Model cartilage as springsModel cartilage as springs• EEnormnorm = 4 MPa, E = 4 MPa, Elesionlesion = 1 MPa, = 1 MPa, ٧٧ = 0.45, = 0.45,
h = thickness, d = compressionh = thickness, d = compressionkn = -E(1- ٧٧)ln(1 – d/h) (1 + ٧٧)(1 – 2 ٧٧)d
ks = 0.02×kn
mmmed lat
0
6
[Blankevoort et al. J Biomech 24: 1019-1031]
Patellofemoral LoadingPatellofemoral Loading
VMOVMO VMLVML VIVI RFRF VLVL
Patellofemoral PainPatellofemoral Pain 4%4% 9%9% 44%44% 22%22% 21%21%Pain FreePain Free 10%10% 12%12% 40%40% 19%19% 19%19%Delayed VMODelayed VMO 0%0% 9%9% 44%44% 22%22% 21%21%
Quadriceps Force Distribution for 30 N-m Extension Moment
[Makhsous et al. Med Sci Sports Exerc 36:1768-75, Zhang et al. J Orthop Res 21:565-71]
Discrete Element AnalysisDiscrete Element Analysis
FM
V = potential energy = spring deformationu = displacement vectorK = stiffness matrixR = force vector
kn
cartilage springs V = 1/2(knn
2+ kss
2)dSV = 1/2{u}T[K]{u}R = V/u = [K]{u}
quads forces
pat tendon forces
Resultant force and moment applied in 5 equal steps
[Elias and Cosgarea, Am J Sports Med 34:1478-85, Elias et al. J Biomech 39:865-72, Elias et al. J Biomech 37:295-302, Elias et al. Am J Sports Med 32:1202-8]
Resultant Force and MomentResultant Force and Moment
40
50
60
70
80
90
100
110
120
30 40 50 60 70 80 90Flexion Angle (degrees)
Late
ral F
orce
(N)
Delayed VMOPatellofmeoral PainPain Free
0.5
1
1.5
2
2.5
3
30 40 50 60 70 80 90Flexion Angle (degrees)
Late
ral T
ilt M
omen
t (N
-m)
Delayed VMOPatellofemoral PainPain Free
VMO
Lat Force
Lat Rot
Lat Tilt
Force applied by VMO decreases lateral force, lateral tilt moment and lateral rotation moment acting on patella
0
0.5
1
1.5
2
2.5
30 40 50 60 70 80 90Flexion Angle (degrees)
Late
ral R
otat
ion
Mom
ent (
N-m
)
Delayed VMOPatellofemoral PainPain Free
Force DistributionForce Distribution
Open symbols significantly different from Open symbols significantly different from Patellofemoral Pain case (p < 0.05)Patellofemoral Pain case (p < 0.05)
70%
72%
74%
76%
78%
80%
82%
84%
86%
30 40 50 60 70 80 90Flexion Angle (degrees)
Late
ral F
orce
Per
cent
age
Delayed VMOPatellofemoral PainPain Free
Maximum PressureMaximum Pressure
Open symbols significantly different from Open symbols significantly different from Patellofemoral Pain case (p < 0.05)Patellofemoral Pain case (p < 0.05)
2
3
4
5
6
7
8
30 40 50 60 70 80 90Flexion Angle (degrees)
Max
Pre
ssur
e (M
Pa)
Delayed VMOPatellofemoral PainPain Free
Cartilage LesionsCartilage Lesions• Lesions identified for 5 kneesLesions identified for 5 knees• Various locations on patella and Various locations on patella and
femurfemur• Lesions increased Lesions increased
pressure, had littlepressure, had littleinfluence on influence on effectiveness of VMOeffectiveness of VMOtrainingtraining
1.5
2
2.5
3
3.5
4
30 40 50 60 70 80 90Flexion Angle (degrees)
Max
imum
Pre
ssur
e (M
Pa)
Pain, With LesionsPain, No LesionsPain Free, With LesionsPain Free, No Lesions
Lesions
Quads Distribution
Patellofemoral Pain Pain Free
LateralMedial
0
2.5
1.25
MPa
40°Patella Lesion
Patellofemoral Pain Pain Free
LateralMedial
0
2
1
MPa
80°Patella Lesion
Trochlear Lesion
ConclusionsConclusions
• Improving VMO function reduces Improving VMO function reduces force applied to lateral cartilage by force applied to lateral cartilage by decreasing lateral force and lateral decreasing lateral force and lateral tilt moment acting on patellatilt moment acting on patella
• Decreasing lateral force, lateral tilt Decreasing lateral force, lateral tilt moment and lateral rotation moment moment and lateral rotation moment acting on patella decrease maximum acting on patella decrease maximum cartilage pressurecartilage pressure
ConclusionsConclusions
• Cartilage lesions increase maximum Cartilage lesions increase maximum cartilage pressurecartilage pressure
• Further modeling of lesions Further modeling of lesions necessary to characterize influence necessary to characterize influence on effectiveness of VMO trainingon effectiveness of VMO training
• Results depend on accuracy of Results depend on accuracy of computational assumptionscomputational assumptions
AcknowledgementsAcknowledgements
• Colorado Institute for TechnologyColorado Institute for Technology