conservative surgical treatments for osteoarthritis: an ... meetings/june anglia 11... ·...

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

(Source: Arthritis Research, UK)

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

3D Model of whole Knee Joint

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

Validation Work in Progress

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.

Thank you