Transcript Determinants of Gait

chapter
12
Ambulation and
Ambulation Aids
Gait
• = A series of rhythmical, alternating movements
of the limbs and trunk that causes a forward
progression of the center of gravity (CoG).
• Involves a repetitive loss and recovery of
balance through displacing and controlling the
motion of the CoG in the most efficient manner
Gait Cycle
• = The series of events that occur between the
heel strike of one limb and the next heel strike
of the same limb.
Figure 12.1a
Gait Components
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Step length: the distance covered between
heel strike (HS) of one limb and HS of the
other limb
Stride length: The distance covered between
the successive HS of one limb and HS of the
same limb
(continued)
Gait Components (continued)
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Cadence: The speed of gait. It can be
measured in the number of steps for a period
of time (usually steps/min).
Cadence and time for gait cycle are related:
The longer the period of time for the gait
cycle, the slower the cadence.
As cadence increases, the time of double
support decreases.
Figure 12.2
Terminology
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HS: heel strike = IC: initial contact
FF: foot flat = LR: loading response
MS: midstance = MS: midstance
HO: heel-off = TS: terminal stance
TO: toe-off = PS: preswing
ES: early swing=IS: initial swing
MSw: midswing = MSw: midswing
LS: late swing = TSw: terminal swing
Gait Cycle Phases
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Stance phase:
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Swing phase:
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62% of the gait cycle
From HS of one limb to toe-off (TO) of same limb
Some or all of the body’s weight borne on the limb
38% of the gait cycle
Time the limb is non-weight bearing
From TO to HS
Double support:
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20% of the gait cycle
Both limbs in contact with the ground
One limb in late stance, other in early stance
Stance Phases
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Heel strike (HS):
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When the heel strikes the ground
Sometimes called foot strike
Foot flat (FF): When entire sole of foot
contacts ground
Midstance (MS): When body is directly over
the limb
(continued)
Stance Phases (continued)
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Heel-off (HO): When heel leaves the ground
but ball of foot remains in contact
Toe-off (TO):
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When toe leaves the ground
Final phase of gait
Swing Phases
Early swing (ES):
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Immediately following TO
Limb CoG begins accelerating forward to move in
front of the body’s CoG
Sometimes called acceleration phase
(continued)
Swing Phases (continued)
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Midswing (MSw):
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Limb passes directly beneath the body.
Tibia is perpendicular to the ground.
Late swing (LS):
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Limb passes in front of the body in preparation for
HS.
Sometimes called deceleration phase.
CoG and Gait
• Purpose of gait is to move the CoG.
• CoG is located approximately anterior to S2.
• During gait, CoG moves from side to side and
from superior to inferior.
(continued)
CoG and Gait (continued)
• Vertical displacement:
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CoG is displaced to vertical peak twice in gait cycle.
Highest point occurs at MS.
Lowest point occurs at double support.
CoG follows sinusoidal path in the vertical direction.
Total vertical displacement is ~2 in. (~5 cm).
• Horizontal displacement:
– CoG is moved from side to side once in gait cycle.
– CoG follows sinusoidal path in the horizontal
direction.
– Total side-to-side displacement: ~1.75 in. (~4.5 cm).
Determinants of Gait
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Six determinants
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Pelvic rotation
Pelvic tilt
Knee flexion at early midstance
Foot and ankle
Ankle and knee
Lateral pelvic motion
Work together to increase gait efficiency
Figure 12.3
Determinants of Gait:
Pelvic Rotation
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Pelvic rotation: ~4° to each side
Pelvis rotates left to right and vertically.
Left-to-right rotation depends on swing limb
(e.g., right limb leads  pelvis rotates to left)
Amount of swing varies with cadence and
step length.
(continued)
Determinants of Gait:
Pelvic Rotation (continued)
Effect of some rotation occurs at both hips
•  Amplitude of sinusoidal wave crest
•  Severity of deflections between wave arcs
•  Severity of impact with the ground
•  Force needed to change direction of CoG
from trough to crest wave
• Smoothes out deflection points
Figure 12.4
Determinants of Gait: Pelvic Tilt
• Pelvic tilt: ~5°to either side
• Pelvis drops inferiorly opposite to weightbearing (WB) limb.
• Some motion occurs at both hips.
– Adduction on WB side
– Abduction on non-weight-bearing (NWB) side
• Effects:
–  Amplitude of sinusoidal wave
– How does this  effectiveness of hip abductor
mechanism?
Determinants of Gait:
Knee Flexion in Early Midstance
• Knee begins to flex immediately after HS and
continues to flex (~15°) until FF.
• Effects:
–  Amplitude of sinusoidal wave crest
–  Severity of deflections between sinusoidal wave
arcs
Figure 12.6
Figure 12.7b
Determinants of Gait: Foot and Ankle
• Talocrural joint
– CoG is falling and WB limb shortens to dampen
impact: Talocrural joint dorsiflexes.
– Plantar flexes immediately following HS to FF.
– Dorsiflexes in MS.
– Begins to plantar flex immediately after MS.
(continued)
Determinants of Gait:
Foot and Ankle (continued)
• Foot
– Pronated by FF.
– Begins to supinate immediately after FF.
• Talocrural center of rotation (CoR) position
changes: high at HS, low at MS, high at TO.
Determinants of Gait: Ankle and Knee
• At HS:
– Knee flexes.
– Ankle CoR moves high to low.
• At FF
– Knee begins extension.
– Ankle CoR remains low.
• At HO
– Knee begins flexing to shorten the limb for swing.
– Ankle CoR rises, then knee flexion increases as
ankle CoR continues to rise.
(continued)
Determinants of Gait:
Ankle and Knee (continued)
• Effects:
–  Severity of the deflections between wave arcs
– Smoothes out the reversal of motion of the CoG at
the low point of its course
• Combinations of knee and ankle motions 
gradual change in functional limb length
throughout gait
Determinants of Gait:
Lateral Pelvic Motion
• Lateral displacement of CoG toward stance
limb could be as much as 6 in.
• Effect: produces lateral movement of CoG
• Hip-knee angle  lateral movement to 1 in.
each side
Figure 12.8a
Figure 12.8b
Figure 12.9
Figure 12.10a
Figure 12.10b
Figure 12.10c
Figure 12.11a
Figure 12.11b
Figure 12.11c
Figure 12.12a
Figure 12.12b