Download Talk 1 – Ankle Biomechanics and Gait Analysis

Ankle Biomechanics
and Gait Analysis
Dr. Tim Daniels
MD FRCSC
Assistant Professor
University of Toronto
Ankle Biomechanics and Gait
Analysis
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Anatomy and Biomechanics of the
ankle joint.
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Histology of ankle cartilage.
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Ankle function during gait.
The Ankle Joint
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Primary motion at
the ankle joint is
in the sagittal
plane as
dorsiflexion and
plantarflexion.
There has been a
misconception
that
biomechanically
the ankle
functions as a
hinged joint
Not a hinged
joint.
The Ankle Joint
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Biplanar motion
external
rotation with
dorsiflexion
internal
rotation with
plantarflexion.
15°
Ankle Rotation
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Cone shaped
articulation.
Rotation of the
ankle joint
occurs around
an axis that
corresponds to
the position of
the deltoid
ligament – also
referred to as
the Apical Angle
A
A>B
B
Ankle Stability
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A single fan shaped
deltoid ligament is
adequate for
medial
stabilization.
Posterior
Tibiocalcaneal
tibiotalar
Anterior tibiotalarligament
ligament
ligament
Tibionavicular
ligament
Ankle Stability
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Larger surface area
laterally – stability
provided by three
separate bands.
Anterior talofibular ligament
Posterior talofibular ligament
The fibula extends more distally
than the medial malleolus thus
providing greater osseous
support on the lateral side.
Calcaneofibular ligament
Ankle Stability
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Larger surface area
laterally – stability
provided by three
separate bands.
Anterior talofibular ligament
Posterior talofibular ligament
The fibula extends more distally
than the medial malleolus thus
providing greater osseous
support on the lateral side.
Calcaneofibular ligament
The foot minus the talus is
considered as one fibro-osseous
unit.
MacConaill and Basmajian
1945
Inherent stability of the ankle is important:
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It is the primary articulation responsible for the
transmission of forces from the ground to the
remainder of the lower extremity.
It is subjected to greater forces per square cm
than any other joint of the body:
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FORCES
CONTACT AREA
Hip = 2 - 3 X body weight
- 1100 mm²
- Knee = 3
- Ankle = 5
- 4 X body weight
- 7 X body weight
- 1120 mm²
- 350 mm²
Ankle Stability
The actual surface area of
the Ankle is larger than the
Knee and Hip - 12 cm²
(Stouffer)
The surface area available to
distribute the forces is
smaller = contact area
The increased surface area aids in stability of the
ankle joint but not in the distribution of forces.
Ankle Stability
The ankle joint is a stable
articulation.
It is supported by three
bony prominences:
Medial malleolus
Lateral malleolus
Posterior malleolus
There is a common misconception
that the ankle is much more stable
in dorsiflexion than it is in
plantarflexion
The Ankle Joint
Ankle Joint
A
5 X body
weight
Foot
Fulcrum
B
A >B
The Ankle Joint
A
B
A>
> B
The Ankle Joint
There is a common misconception
that the ankle is much more stable
in dorsiflexion than it is in
plantarflexion
Lever Arm
A >B
A
B
The Ankle Joint
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The ankle joint is subjected to the highest
forces per square centimetre.
It is more commonly injured than any
other joint in the body.
Yet, the incidence of symptomatic ankle
arthritis is approximately nine times lower
than that of the knee and hip.
The Ankle Joint
(Histology)
Articular cartilage thickness:
• Knee - 1 to 6 mm
• Ankle - 1 to 1.7 mm
u  Ankle cartilage is more uniform in nature when
compared to the knee and hip.
u  Ankle cartilage is stiffer than the knee and hip.
u  Talar cartilage is more resistant to physiologic
stresses created by cyclical loading.
u  Ankle cartilage more resistant to the actions of MMP
(matrix mealloprotinases) than the knee and hip.
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Ankle Joint Function
during the Gait Cycle
The Foot functions as a Rocker
The Ankle Joint
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Subjected to the
greatest forces.
Lowest contact
area.
Most commonly
injured joint.
Remarkably
resilient to the
development
of
Osteoarthritis
The ankle appears to be protected
from the development of OA by its:
Metabolic properties
u  Uniform cartilage mantle
u  Congruency
u  Stability
u  Restrained movement
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