THE ENGINEERING IN YOUR
JOINTS AND WHAT CAN GO
WRONG
N G SHRIVE
What Problems are We Trying to Solve
and Why?
Arthritis = “Inflamed Joint”
Need Compared to Other Diseases
Visits to Physicians
Cardiovascular Disease
9
Cancer
8
Bone & Joint Disorders
Millions
7
6
5
4
3
2
1
0
Year
Each year, one of every three Albertans sees a healthcare provider for a
bone & joint problem. 24% of visits to a physician are for MSK disorders.
Rogue’s gallery
Typical sketch of Synovial Joint
Actual Joints more complicated
Engineering Requirements of
Joints
• Transmit Loads between Bones
• Allow Relative Motion Between Bones
– Tribology (lubrication)
– Stabilization (Constrained Motion within
Range)
Muscles & Joints – a compromise
b
M
W
a
W
Muscles & Joints – a compromise
a
L`
S`
M`
a = 7b
M = 7W
M
S
L
Kinematic Advantage
Mechanical Disadvantage
Compressive Force across joint = 6W
Engineering Requirements of
Joints
• Supply nutrients and remove waste from
cells
• Perform task over lifetime
A Joint is an Organ – Roles of Tissues
• Loads
– Compression (Cartilage, Menisci, Labra, Bones)
– Tension (Ligaments, Tendons, Bones)
– Shear (Ligaments, Menisci, Bones)
– Moments (All)
(ALL INFLUENCED BY JOINT GEOMETRY)
A Joint is an Organ – Roles of Tissues
• Constrained Motion - Stability
– Ligaments, Capsule, Joint Geometry
• Lubrication
– Synovial fluid, Cartilage
A Joint is an Organ
• Synergism of components
• Failure of one component leads to
alteration/adaptation in other components
– including the underlying bone
• The tissue least able to adapt fails
mechanically
Constrained Motion Ligaments
Flexion/Extension Kinematics
Section of knee joint
Section of knee joint
The Cruciate Four-bar Chain
C
A
B
D
The Cruciate Four-bar Chain
B
C
C
B
C
B
A
A
A
D
D
B
T
T
C
C
B
C
T
B
A
A
X1
R
D
D
A
X2
R
D
X3
R
D
Fibre Recruitment
Ligament Histology

Longitudinally oriented parallel
collagen fibres. (In white)

Elongated cells (fibroblasts) in
rows between collagen fibres.
(In black)
Fibre
“Crimp” in an
unloaded ligament
Ligament Stress-Strain Curve
s
LINEAR
REGION
TOE REGION
(5% strain,14 MPa)
e
Creep
so
s
so
eo
e
t
t
Static Creep Strain +/- s.d. (%)
2.0
1.5
Relative insensitivity to
toe region stresses
*
1.0
0.5
0.0
4.1
7.1
14
Creep Test Stress (MPa)
* = different (p<0.05) than
at lower stresses
28
Creep
CRIMP
CRIMP
Pre-Creep
Post-Creep
e
t
Crimp Analysis: Creep
Pre-Creep
80% Crimped
20% Straight
Image Sizes 370 x 280 m
Post-Creep
24% Crimped
76% Straight
Load Transmission across
Diarthrodial Joints
Typical sketch of Synovial Joint
Cartilage Layer
• Thin
• Much less stiff than
bone
• ~ 80% water
Structure of Articular cartilage
In Diarthrodial Joints, have menisci,
or labra
• Mensiscus in the knee
In Diarthrodial Joints, have menisci,
or labra
• Glenoid labrum in the shoulder
In Diarthrodial Joints, have menisci,
or labra
• Acetabular labrum in the hip
Joint surfaces are Incongruous
Contact starts on the periphery
Finite Element Models
• Geometry
Gap
• Material properties
• Contact simulation
500N in 0.05sec.
Gap
Full Congruency
Finite Element Models
• Geometry
• Material properties
• Contact simulation
 = 0.002
Free drainage
Sealed surfaces
Results
• Pore Pressures
• Stresses perpendicular to the interface
• Stresses parallel to the interface
• Circumferential stresses
FEM Conclusion
• A small inner gap is good … but…
Pressure
S11
S22
S33
What is Effect of menisci and
labra?
Results
• Pore Pressures
• Stresses perpendicular to the interface
• Stresses parallel to the interface
• Circumferential stresses
How do menisci and Labra carry load?
Force transmission
Radius
Axis of
Symmetry
A
C
C
B
Radial
component
Applied
pressure
direction
Radial
component
Annulus
Vertical
component
Fc
Tangential
component
Fr
Annulus, C
Vertical
reaction
Fc
"Radial" components of
applied pressure
Tangential
component
Radial
component
displacement
ndentor
Circumferential stiffness
Original Position
Radial expansion
Original Position
Radial expansion
Vertical displacement
ofVertical
indentordisplacement
Final Position
of femur
Vertical displacement
of indentor
Final Position Vertical displacement
of femur
Meniscus fibres
Reconstruction of the Fibre pattern of the meniscus
Bullough, P. G., et al., (1970). The Journal of Bone and Joint Surgery. 52(B), No. 3. 564-570
Results & cell phenotype
*Hellio Le Graverand, et al. (2001).
J. Anat. 198:525-535
C
B
A
Lubrication
(and nutrient supply)
Pure fluid film lubrication: the fluid film between
the surfaces can be maintained by three
mechanisms – hydrostatic; squeeze film;
hydrodynamic
Boundary Lubrication: lubricant molecules
stick to the surfaces, keeping them apart
Continued Debate
In the lower limb
• Boundary Lubrication during load bearing?
– High load, “low” relative movement of
surfaces
• Fluid film during swing
– Low load, “high” relative speed of surfaces
What can go wrong?
Inflammatory Arthritis
Life threatening disease: >10,000 Albertans
Joint Injuries – “Sprains”
1:6 active people sprain a joint each year
Joint Injury
• Inflammation
– Acute
– Chronic
• Instability
• Change in loading?
Typical Meniscal tear
Result of Meniscectomy:
Pore Pressures @ 1050N
Osteoarthritis
Osteoarthritis
The Stages of Pathology of OA
progressive loss of hyaline cartilage
4 Grades:
• Soft and/or cracking
• Surface loss
(inflamed)
• Deeper loss
(inflamed+)
• Full thickness loss
– (Bone pain++++)
Ligament Healing
•
•
•
•
•
Gaps fill with new material
“SCAR”
Not organized like normal
Scar full of “flaws”
“Remodels” (alignment and
sizes of collagen fibrils)
Scar Composition
• Somewhat similar to normal
• BUT some key differences
• Changing over time
Soft Tissue Repair
•
•
•
•
•
•
Chemical Composition is not reproduced
Flaws not removed
Fibre orientation not complete
Fibre sizes not restored
Connectivity not restored
Consequences
– Reduced strength
– Greater creep
– Laxity
LCL Fibril Diameter Changes
N
% of total
50
Tx
Normal
ACL/MCL Tx
0
Collagen Fibril Diameter of Ligament
(48nm in each class)
30,000x
PCL Fibril Diameter Changes
N
Tx
% of total
50
Normal
ACL/MCL Tx
0
Collagen Fibril Diameter of Ligament
(48nm in each class)
30,000x
Conclusions
• Joints are organs
• Load bearing across joints and in
ligaments provides elegant solutions to
potential problems, given the materials
• Disruption to one component will affect all
others
• Need a lot more research
Acknowledgements
The many who have contributed to the
development of these perspectives –
including Cy Frank, Dave Hart, Ron
Zernicke, John O’Connor, John Matyas, JB
Rattner, Gail Thornton, Judith Meakin,
Samer Adeeb, Linda Marchuk, Ezz SayedAhmed, Marie-Pierre Helio Le Graverand,
Ashraf Ali, Sandra Martelli, Lara
Malmqvist, Frank van der Voet, Kaz
Simbeya, summer students, technical
staff…….
Funding Acknowledgements
QUESTIONS ?