EVALUATION OF A NOVEL

TECHNIQUE TO MAP THE

BIOMECHANICAL PROPERTIES OF

ENTIRE ARTICULAR SURFACES

USING INDENTATION

S. Sim1, 2, E. Quenneville2, M. Garon2, C.D. Hoemann1, M. Hurtig3 and M.D. Buschmann1

1. Biomedical & Chemical Engineering, Ecole Polytechnique de Montreal, Montreal, QC, Canada

2. Biomomentum Inc., Laval, Qc, Canada

3. Comparative Orthopaedic Research Laboratory, Department of Clinical Studies, University of Guelph, Guelph, Ontario, Canada

ICRS 2013

Purpose • Mechanical testing of articular cartilage is a useful outcome measure in studies of

cartilage degeneration and cartilage repair.

• Mechanical testing can be done in different experimental configurations:

Indentation Compression

Shear Torsion Tension

Bending

Practical Advantages

of Indentation

• Cartilage need not be harvested

from the articular surface

• Minimal disruption of the articular surface

• Maintains the mechanical environment of the cartilage layer and its

interaction with the subchondral bone

• Testing multiple sites

Indentation requires the compression axis

aligned perpendicular to the articular surface.

Mathematical models are more complex in

indentation with a spherical indenter.

Picture from: http://www.kneeclinic.info/

Articular surface

Tide mark

Calcified cartilage Subchondral bone

Cancellous bone

However

Methods

Thickness

is missing

• Automated Perpendicular Indentation:

spherical indenter for a new automated indentation technique

multiaxial load cell – uses Fx, Fy and Fz to calculate the normal force

3-axis mechanical tester – uses 3 displacement components to provide

a perpendicular displacement based on the surface orientation

Contact coordinates (x,y,z)

of predefined positions and 4

surrounding positions

Surface orientation

(θz)

Normal

force/displacement vs

time

Methods

Thickness

is missing

• Automated Perpendicular Indentation:

spherical indenter for a new automated indentation technique

multiaxial load cell – uses Fx, Fy and Fz to calculate the normal force

3-axis mechanical tester – uses 3 displacement components to provide

a perpendicular displacement based on the surface orientation

Contact coordinates (x,y,z)

of predefined positions and 4

surrounding positions

Surface orientation

(θz)

Normal

force/displacement vs

time

Methods

Thickness

is missing

• Automated Perpendicular Indentation:

spherical indenter for a new automated indentation technique

multiaxial load cell – uses Fx, Fy and Fz to calculate the normal force

3-axis mechanical tester – uses 3 displacement components to provide

a perpendicular displacement based on the surface orientation

Contact coordinates (x,y,z)

of predefined positions and 4

surrounding positions

Surface orientation

(θz)

Normal

force/displacement vs

time

Methods

Thickness

is missing

• Automated Perpendicular Indentation:

spherical indenter for a new automated indentation technique

multiaxial load cell – uses Fx, Fy and Fz to calculate the normal force

3-axis mechanical tester – uses 3 displacement components to provide

a perpendicular displacement based on the surface orientation

Contact coordinates (x,y,z)

of predefined positions and 4

surrounding positions

Surface orientation

(θz)

Normal

force/displacement vs

time

Methods

Thickness

is missing

• Automated Perpendicular Indentation:

spherical indenter for a new automated indentation technique

multiaxial load cell – uses Fx, Fy and Fz to calculate the normal force

3-axis mechanical tester – uses 3 displacement components to provide

a perpendicular displacement based on the surface orientation

Contact coordinates (x,y,z)

of predefined positions and 4

surrounding positions

Surface orientation

(θz)

Normal

force/displacement vs

time

Methods

• Thickness measurement:

Technique adapted from Jurvelin et al., 1995

Position of the

cartilage surface Position of the

subchondral bone

Vertical

force/displacement vs

time

Thickness can

be obtained

Methods

• Thickness measurement:

Technique adapted from Jurvelin et al., 1995

Position of the

cartilage surface Position of the

subchondral bone

Vertical

force/displacement vs

time

Thickness can

be obtained

Analysis – Thickness

Vertical

Distance

Thickness = vertical distance x cosine (surface orientation)

Surface orientation

Cartilage

surface Subchondral

bone

Analysis – Automated Indentation

Instantaneous Modulus

(MPa)

Elastic Model

in Indentation

(Hayes, 1972)

Using the known

thickness

No

rmal

Fo

rce

(N

)

Spherical

indenter

Intradermal Bever

Needle

from Precision Glide

Camera

from Point Grey

Research

Radius of 0.5 mm Needle size of 26G 3/8” FMVU USB 2.0

Methods

Mach-1 v500css

from

Biomomentum Inc.

Multiaxial mechanical

tester

Device Equipment

Methods

• Mechanically-Controlled Surface Mapping

sample

camera

picture (1280x960 pixels)

position grid superimposed

converted in units of length (mm)

MACH-1

Methods • Samples:

Ovine Murine

current use in articular

cartilage repair studies

use in many disease and

developmental studies

Male Male

100-140 lbs 0.08 lbs

4-5 y.o Mature

No indications of joint pathology

Visually normal tibial plateau and femoral condyles were collected from

closed stifle joints

Pictures from: http://www.123rf.com/

Small dimensions

To reveal the high

spatial resolution and

sensitivity of this novel

technique

Results

≈ 150 measurements/articular surface

≈ 1 minute per indentation

≈ 30 seconds per thickness

3

D

S

U

R

F

A

C

E

Verifier le

graphique Fmax

vs. Angle pour voir

corriger

compliance ou

non

Discussion Works with any type of articular

cartilage as thin as murine.

Thickness obtained are in line with those

reported in the literature (Stockwell et al., 1971;

Frisbie et al., 2006).

Results can also be fit with poroelastic models,

e.g. the fibril-reinforced poroelastic model where

the permeability, the matrix modulus and fibril

modulus can be extracted.

≠ Aggregate Modulus: a measure of

stiffness of the tissue at equilibrium

when all flow fluid has ceased.

Discussion • Possible applications:

• Characterization of articular surfaces in cartilage

repair studies

• Monitoring of cartilage degeneration

• Monitoring of the mechanical properties in

knockout mice knee joints

• Characterization of bone, skin or

different materials for implants

Pictures from: http://www.genome.gov/

Conclusions

• This novel indentation mapping technique allows

to highlight the spatial variation over the entire

surface.

• A promising tool for studies that need to

characterize mechanical properties of the

articular surface.

Acknowledgement

• Funding provided by National Sciences and

Engineering Research Council (NSERC),

the Fonds du recherche du Québec -

Nature et technologies (FRQ-NT) and

Biomomentum Inc.

Questions