Transcript VARIABLE CADENCE KNEES Overview and Brainstorm of Training Strategies Tony Fitzsimons Peter Spooner-Hart Dr Ian Jennsen.

VARIABLE CADENCE KNEES
Overview and Brainstorm of
Training Strategies
Tony Fitzsimons
Peter Spooner-Hart
Dr Ian Jennsen
Content
 Summary of general principles
 Types of knees
 Brainstorm Training Ideas
Prescription
 Depends on users needs, physical potential,
and goals.
1. Needs
 Extra stance phase stability:
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Short stumps
Bilateral involvement
Physical limitation to hip muscular control
Fear / decreased confidence
 Reduce energy requirements
1. Needs (cont)
 Mobility Needs:
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Stand
Transfer
Walk – level
Walk – uneven ground
Slopes / ramps
Stairs
Curbs
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Grass
Jog / run
Vary pace
No aids / hands free
Dual task: talk, carry
objects, interact with
environment (pets,
children, escalators…)
2. Physical Potential
 K2 and above:
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The patient has the ability or potential for
ambulation with the ability to traverse low-level
environmental barriers such as curbs, stairs or
uneven surfaces. Typical of the limited
community ambulator.
2. Physical Potential (cont)
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Residual limb length.
Muscle strength.
Range of motion.
Balance.
Proprioception.
Cognition.
Involvement of other limb.
Co-morbidities.
3. Goals
 Higher level community ambulators.
 Work or recreational needs.
 Negotiation of uneven surfaces.
 Motivation with program.
Types of Knees
 Need to try to mimic function of
anatomical knee:
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Polycentric.
Respond to changes in velocity.
Provide stability in stance phase:
Yield / shock absorption.
 Support body weight.
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Shorten limb for foot clearance.
Types of Knees
 Mechanical:
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Geometric locking.
Hydraulic / pneumatic.
Polycentric / single axis
 Microprocessor controlled:
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Hydraulic
Magnetorheologic
Types of Knees
 Important for Physiotherapists to be aware of the
characteristics and differences of the knee joints
and their functionality:
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Whether they “lock” in stance phase
How they “release” for swing phase
Will they allow flexion under load – stairs, ramps,
sitting?
Ability to engage / disengage hydraulics
 Not all knees will have the same advantages /
disadvantages!
Advantages
 Kinematics / Kinetics:
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Flexion yield at weight
acceptance: (Sutherland 1997)
Shock absorption
 No excessive elevation of
Centre of Mass
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Reduced hip extensor
activity during early
stance (Johansson et al 2005)
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Decreased need to use
extensors to lock knee
Advantages
 Kinematics / Kinetics
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Improved terminal hip extension (Total knee vs
normal or 4-bar linkage, Sutherland et al 1997)
Increased contralateral step length (17% with
Total knee vs 4-bar linkage, Sutherland et al 1997)
Advantages
___normal
….4-bar
---Total knee
(Sutherland et al 1997)
Advantages
 Kinematics / Kinetics:
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Reduced hip flexor demand at swing initiation
(Johansson et al 2005, Blumentritt et al 1998)
Better mechanical advantage (more initial extension)
 Knee not locked in “hyperextension” (NB Knee
flexion commences later through stance; Sutherland et al 1997)
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Reduced compensatory strategies such as hip
hiking, circumduction.
Polycentric knees allow shortening of limb for
better foot clearance.
Control of terminal impact during late swing.
Advantages
___normal
….4-bar
---Total knee
(Sutherland et al 1997)
Advantages
 Increased velocity:
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18%, total knee c/w 4-bar linkage knee (Sutherland et al 1997)
 Variable cadence:
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Swing phase adapts to speed of walking.
 Reduced energy consumption
 Decreased trauma to residuum
 Decreased work of contralateral limb (Schmalz 2002)
(Farber et al 1995, Johansson et al 2005)
(Farber et al 1995)
Advantages
 Flexion under load
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Hydraulic knees
More natural stand sit.
 Descent of ramps / stairs.
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Advantages
 Stumble recovery
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Weight activated stance control (Hydraulic
knees: 3R80, Mauch, C-leg, Rheo)
Disadvantages
(Disadvantages may depend on model of knee)
 Generally heavier than safety knee.
 Sometimes difficult to align knees level with longer
stumps.
 Sitting down:
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Not always supportive during movement
May have to unload knee to disengage stance features,
OR
Extend knee and load toe to disengage stance features
Disadvantages
 Load toe – may disengage stance support
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Beware of some tasks:
Forceful hyperextension
 Walking / stepping backwards
 Stepping down backwards (off stool, ladder, etc)
 Foot position during some standing / reaching tasks.
 Loading forefoot with knee extended while on uneven
ground.
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Disadvantages
 Increased need for manual adjustment as user
capabilities change (or is this an Advantage?)
 Lack of mid-stance knee extension
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(with knees with stance phase yielding, eg Total Knee
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May impact on contralateral swing phase
Sutherland et al 1997
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 Method of suspension – drop-off and control issues
with pelvic band. Do not tend to get as much out of
the knees if not securely attached to stump.
Disadvantages
___normal
….4-bar
---Total knee
(Sutherland et al 1997)
Types of Knees
 Demonstration…
Training – General Principles
 Strength.
 Range of motion.
 Balance.
 Proprioception.
 Correct movement patterns.
 Confidence to load knee with correct timing
& alignment.
Weight Acceptance
 Hip extensor activity.
 Forward shift of pelvis – timing of loading
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eg 3R80 has stance sensitivity engagement
setting – must load joint to engage hydraulic (Schmalz
et al 2002)
Stance phase activation
 Prosthetic alignment…
Stance phase activation
 Patient alignment…
Weight Acceptance
 Correct trunk alignment to ensure correct
timing of loading response and GRF
positioned to activate stance control.
Mid stance
 Maintain trunk control
 Maintain hip extensor activity
 Control lateral movement
Late Stance / Swing Initiation
 Hip extension range.
 Burst of hip flexor activity.
 Must load toe during late stance to disengage
stance control features.
Late Swing
 Knee must be in extended position in order
for stance control features to be activated at
weight acceptance.
Brainstorm
 Training ideas:
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Walking on level ground.
Walking downstairs.
Walking down slopes.
Other activities…
Brainstorm – stance yield knees
 Getting used to the feel of engaging the hydraulic
mechanism…
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Practice stand sit, riding the hydraulic down.
Step and load: (+/- hand support)
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On flat ground. Find the “sweet spot” where hydraulic resistance
kicks in.
Down from a step with prosthetic limb. Assists in unloading
contralateral limb and forward shift of weight to weight
acceptance on prosthetic limb.
Down from a step on to a wedge (simulates a ramp, and causes
knee to move towards flexion).
Brainstorm – stance yield knees
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Step & load, lift intact limb.
Step & load, and turn towards intact side while weight is borne
on the (flexing) prosthetic side.
Walking:
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Gait correction – pelvic rotation, trunk rotation, reduce lumbar
lordosis and improve terminal hip extension.
Improve confidence to load limb at weight acceptance,
maintaining forward shift of body weight.
Down slopes – at heel strike the knee will tend towards flexion,
so amputee must learn to load properly to engage the hydraulic
resistance.
Brainstorm – stance yield knees
 Remember to seek advice from prosthetists, eg:
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Tweaking stance phase resistance as amputee improves.
Tweak swing phase resistance if swing occurs too slowly,
or there are other abnormalities such as overuse of hip
flexors to initiate swing phase flexion (or late swing
extension), or if the toe catches in early swing due to
underused hip flexors.