Transcript Slide 1

Biomechanics of Walking
for People with
Lower Extremity Amputations
Dave Thompson PT
http://moon.ouhsc.edu/dthompso/
Update on Lower Extremity Amputations
September 28, 2006
1
Objectives
• List the gait deviations that are most common in
people who wear prostheses, and explain their
most frequent causes.
• Explain how changes in prosthetic alignment
alter the position of the ground reaction force and
affect prosthetic joint movement during gait.
• Explain how prosthetic foot alignment affects the
alignment of a person's residual limb inside a
prosthetic socket.
Update on Lower Extremity Amputations
September 28, 2006
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When is someone ready for a
prosthesis?
• when he or she can control the knee joint
well enough to walk safely.
Update on Lower Extremity Amputations
September 28, 2006
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Controlling the knee joint:
Forces that affect
joint position and
movement during
stance:
• ground reaction
• muscles
• joint reaction
Update on Lower Extremity Amputations
September 28, 2006
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Ground reaction force (GRF)
• GRF is equal in magnitude
and opposite in direction to
sum of gravitational and
inertial forces
• Assess GRF’s effect on joint
movement in customary way,
by evaluating its location with
respect to joint axis.
Update on Lower Extremity Amputations
September 28, 2006
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A useful simplification:
Moments produced by GRF and
muscles are equal and opposite.
Mmm = -Mgrf
Update on Lower Extremity Amputations
September 28, 2006
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Moments produced by GRF and
muscles are equal and opposite.
During loading response,
GRF’s sagittal plane location
is:
• posterior to ankle axis
• posterior to knee axis
• anterior to hip axis
Update on Lower Extremity Amputations
September 28, 2006
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To preserve stability, people with
amputations can compensate for
absent or weak muscles by:
1. substituting another muscle in a
closed chain
2. moving joint axis to  GRF’s
moment about joint.
3. moving GRF to  its moment
about joint.
Update on Lower Extremity Amputations
September 28, 2006
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Controlling the knee joint during
loading response:
People with
amputations can
activate muscles to
control residual and
prosthetic joints:
• Knee extensors
(in TT prosthesis)
• Hip extensors
• Hip abductors /
rotators
Update on Lower Extremity Amputations
September 28, 2006
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A less useful way to control the knee
joint during loading response:
reposition knee joint
axis posteriorly to 
GRF’s moment
about joint
by posterior rotation
of pelvis
Update on Lower Extremity Amputations
September 28, 2006
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Prosthetic alignment can help control
knee joint during loading response:
Position
prosthetic
foot so
origin of
GRF is more
anterior.
Update on Lower Extremity Amputations
September 28, 2006
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Moments produced by GRF and
muscles are equal and opposite.
During preswing, GRFV’s
sagittal plane location is:
• anterior to ankle axis
• posterior to knee axis
• posterior to hip axis
Update on Lower Extremity Amputations
September 28, 2006
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Initiation of knee flexion
during preswing
GRF initiates prosthetic knee
flexion if it is posterior to
knee joint axis.
• Heel must rise.
• Pelvis must rotate
forward, moving the femur.
• Body weight must
transition smoothly from
trailing to forward limb.
Update on Lower Extremity Amputations
September 28, 2006
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Poor preswing initiation of knee flexion
Four probable causes
•  GRF
•  fwd pelvic rotation
•  hip flexor action
• Prosthetic alignment that
delays heel rise.
Update on Lower Extremity Amputations
September 28, 2006
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Moments produced by GRF and
muscles are equal and opposite.
During loading response,
GRF’s frontal plane location
is:
• lateral to subtalar axis
• medial to knee
• medial to hip axis
Update on Lower Extremity Amputations
September 28, 2006
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Hip abductors counter
GRF’s adductor moment
Figure from Gottschalk et al. (1989).
Does socket configuration influence
the position of the femur in aboveknee amputation? Journal of
Prosthetics and Orthotics, 2, 94-102.
http://www.oandp.org/jpo/library/1990_01_
094.asp
Update on Lower Extremity Amputations
September 28, 2006
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Lateral trunk lean reduces GRF’s hip
adductor moment
Update on Lower Extremity Amputations
September 28, 2006
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Objectives
• List the gait deviations that are most
common in people who wear prostheses,
and explain their most frequent causes.
Update on Lower Extremity Amputations
September 28, 2006
18
Objectives
• Explain how changes in prosthetic
alignment alter the position of the ground
reaction force and affect prosthetic joint
movement during gait.
• Explain how prosthetic foot alignment
affects the alignment of a person's
residual limb inside a prosthetic socket.
• http://moon.ouhsc.edu/dthompso/gait/pobmk/frames.htm
Update on Lower Extremity Amputations
September 28, 2006
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