VARIABLE CADENCE KNEES

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VARIABLE CADENCE KNEES

• Overview and Brainstorm of
• Training Strategies
• Tony Fitzsimons
• Peter Spooner-Hart
• Dr Ian Jennsen

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Content

• Summary of general principles
• Types of knees
• Brainstorm Training Ideas

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Prescription

• Depends on users needs, physical potential, and
  goals.

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1. Needs

• Extra stance phase stability
• Short stumps
• Bilateral involvement
• Physical limitation to hip muscular control
• Fear / decreased confidence
• Reduce energy requirements

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1. Needs (cont)

• Mobility Needs
• Stand
• Transfer
• Walk level
• Walk uneven ground
• Slopes / ramps
• Stairs
• Curbs

• Grass
• Jog / run
• Vary pace
• No aids / hands free
• Dual task talk, carry objects, interact with
  environment (pets, children, escalators)

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2. Physical Potential

• K2 and above
• 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.

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2. Physical Potential (cont)

• Residual limb length.
• Muscle strength.
• Range of motion.
• Balance.
• Proprioception.
• Cognition.
• Involvement of other limb.
• Co-morbidities.

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3. Goals

• Higher level community ambulators.
• Work or recreational needs.
• Negotiation of uneven surfaces.
• Motivation with program.

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Types of Knees

• Need to try to mimic function of anatomical knee
• Polycentric.
• Respond to changes in velocity.
• Provide stability in stance phase
• Yield / shock absorption.
• Support body weight.
• Shorten limb for foot clearance.

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Types of Knees

• Mechanical
• Geometric locking.
• Hydraulic / pneumatic.
• Polycentric / single axis
• Microprocessor controlled
• Hydraulic
• Magnetorheologic

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Types of Knees

• Important for Physiotherapists to be aware of the
  characteristics and differences of the knee
  joints and their functionality
• 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!

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Advantages

• Kinematics / Kinetics
• Flexion yield at weight acceptance (Sutherland
  1997)
• Shock absorption
• No excessive elevation of Centre of Mass
• Reduced hip extensor activity during early stance
  (Johansson et al 2005)
• Decreased need to use extensors to lock knee

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Advantages

• Kinematics / Kinetics
• 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)

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Advantages
___normal .4-bar ---Total knee (Sutherland et
al 1997)
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Advantages

• Kinematics / Kinetics
• 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)
• 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.

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Advantages
___normal .4-bar ---Total knee (Sutherland et
al 1997)
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Advantages

• Increased velocity
• 18, total knee c/w 4-bar linkage knee
  (Sutherland et al 1997)
• Variable cadence
• Swing phase adapts to speed of walking.
• Reduced energy consumption (Farber et al 1995,
  Johansson et al 2005)
• Decreased trauma to residuum (Farber et al 1995)
• Decreased work of contralateral limb (Schmalz
  2002)

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Advantages

• Flexion under load
• Hydraulic knees
• More natural stand ?sit.
• Descent of ramps / stairs.

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Advantages

• Stumble recovery
• Weight activated stance control (Hydraulic knees
  3R80, Mauch, C-leg, Rheo)

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Disadvantages

• (Disadvantages may depend on model of knee)
• Generally heavier than safety knee.
• Sometimes difficult to align knees level with
  longer stumps.
• Sitting down
• Not always supportive during movement
• May have to unload knee to disengage stance
  features,
• OR
• Extend knee and load toe to disengage stance
  features

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Disadvantages

• Load toe may disengage stance support
• 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
• (with knees with stance phase yielding, eg Total
  Knee Sutherland et al 1997)
• May impact on contralateral swing phase
• 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.

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Disadvantages
___normal .4-bar ---Total knee (Sutherland et
al 1997)
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Types of Knees

• Demonstration

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Training General Principles

• Strength.
• Range of motion.
• Balance.
• Proprioception.
• Correct movement patterns.
• Confidence to load knee with correct timing
  alignment.

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Weight Acceptance

• Hip extensor activity.
• Forward shift of pelvis timing of loading
• eg 3R80 has stance sensitivity engagement setting
  must load joint to engage hydraulic (Schmalz et
  al 2002)

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Stance phase activation

• Prosthetic alignment

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Stance phase activation

• Patient alignment

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Weight Acceptance

• Correct trunk alignment to ensure correct timing
  of loading response and GRF positioned to
  activate stance control.

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Mid stance

• Maintain trunk control
• Maintain hip extensor activity
• Control lateral movement

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Late Stance / Swing Initiation

• Hip extension range.
• Burst of hip flexor activity.
• Must load toe during late stance to disengage
  stance control features.

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Late Swing

• Knee must be in extended position in order for
  stance control features to be activated at weight
  acceptance.

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Brainstorm

• Training ideas
• Walking on level ground.
• Walking downstairs.
• Walking down slopes.
• Other activities

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Brainstorm stance yield knees

• Getting used to the feel of engaging the
  hydraulic mechanism
• Practice stand ?sit, riding the hydraulic down.
• Step and load (/- hand support)
• 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).

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Brainstorm stance yield knees

• Step load, lift intact limb.
• Step load, and turn towards intact side while
  weight is borne on the (flexing) prosthetic side.
• Walking
• 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.

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Brainstorm stance yield knees

• Remember to seek advice from prosthetists, eg
• 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.