Conservative surgical treatments
for osteoarthritis: An integrated
computational and in-vitro study
Diagarajen Carpanen, Franziska Reisse, Yazan Deri, Kevin Cheah,
John Dowell, Howard Hillstrom, Rob Walker, Rajshree Mootanah
Introduction
Osteoarthritis (OA) : degenerative disease of all the tissues in the
di-arthrodial joint leading to pain, limited mobility and joint
deformation.
14.1% of men & 22.8% of women over 45 years show symptoms
of OA of the knee.
OA costs £12 billion to the NHS and $185.5 billion to the United
States annually
Common Causes of Knee Osteoarthritis
• Joint injury - a torn meniscus or
ligament which can result from a twisting
injury ( football, skiing ).
• Knee malalignment – 4x more prone to
develop OA (Sharma, L., 2001)
• High tibial osteotomy (HTO) is a surgery aiming to relieve pain and
restore high-level function in active patients by re-aligning the lower limb
and lowering the contact stress in the knee joint.
• Partial meniscectomy is an arthroscopic surgical procedure commonly
performed to resect the injured part of the meniscus to relieve
symptoms and restore knee function.
High Tibial Osteotomy &
Partial Meniscectomy
Gap in Knowledge
•The underlying link between malalignment and stress in the knee
compartment is not well understood and surgical realignment
outcomes by HTO have been unpredictable for unknown reasons
•Effects of resecting specific sizes and locations of meniscus on
knee joint contact stress and the risk of osteoarthritis onset is not
clear.
In Vitro investigations
• A custom-made experimental rig has been designed to
work in conjunction with an Instron 8874 testing machine.
•The rig simulates the ‘sit to stand’ movement, which
places considerable demand on the menisci.
•Sheep knee specimens were used for this study.
•A compressive axial load was transmitted to the proximal
femur by a ball and socket fixture.
•A controlled load was applied to achieve 0 to 70° flx-ext.
Preliminary Results
•A Tekscan K-scan high resolution
sensor array measured contact area,
peak contact stress, and mean
contact stress in the knee joint.
•Higher medial compartment stress
resulted from partial meniscectomy
compared to the intact knee.
Computational Investigations
Created a 3D model of the knee joint from CT and MRI data of a
cadaveric specimen using MIMICS
Exported the 3D model to finite element packages where boundary
conditions (forces and constraints) were applied for stress analyses in
the knee joint
3D Knee Model Development
CT ImageMRI scan
Femur
FibulaTibia
Femoral Cartilage
Meniscus
Tibial Cartilage
Image Registration of Osseous &
Soft Tissues
3D MRI model was registered to the 3D CT model.
Point and global registration techniques were
employed, using the minimum RMS error.
Non-manifold Assembly (NMA)
The NMA algorithm permits elimination of sections between surfaces.
This ensures that a common border is calculated
Finally a volume mesh for NMA was created
Preliminary FEA Studies
• Healthy knee
• Knee with a total
meniscectomy
• Knee with malalignment
Material Properties
employed
Young’s
Modulus
[MPa]
Poisson’s Ratio
Bones 1000 0.3
Cartilage 50 0.45
Meniscus 112 0.45
Ligaments 400 0.45
Source: Kubicek, M. and Florian,Z., 2009
FEA – Contact Definitions
Labelling Contact Pair
1 Tibial cartilage - meniscus
2 Femoral cartilage - meniscus
3 Femoral cartilage – tibial cartilage
4 Tibia - fibula
• Contact Surfaces are allowed to touch but not penetrate.
FEA – Boundary Conditions
Solve for stress at static equilibrium to
simulate standing on one leg:
1. Fix the distal tibia and fibula (A & B).
2. Apply axial load at the proximal femur (C).
3. Set constraints (D):
• Translation free in vertical direction only
• Flx/ext constrained to sagital plane
• Other rotational degrees of freedom free
Preliminary Results
P: posterior
A: anterior
M: medial
L: lateral
P
L
A
M
Intact knee ~ 2.6 MPa
After Total Meniscectomy ~ 4.9 MPa
Malaligned Knee ~ 4.2 MPa
Validation Work in Progress
• Faxial = 300N
• knee = 0°• Mvarus = 0 to 12Nm
• Error analysis between joint contact stress
and predicted model stress in progress
QuickTime™ and aMicrosoft Video 1 decompressorare needed to see this picture.
A
P
ML
P: posterior
A: anterior
M: medial
L: lateral
Conclusion
Preliminary findings show
• the importance of the meniscus in reducing knee joint
contact stresses.
• that malaligned knees are subjected to high stress levels
which indicates the importance of understanding realigning
(e.g. HTO) surgical techniques.
Further Works
• Simulation of HTO and partial meniscectomies.
• Sensitivity analysis:
- on element size for each osseous and soft tissue structure.
- alter the geometries and material properties of bones and
soft tissues to investigate how these parameters affect
knee joint contact stresses.
