VARIABLE CADENCE KNEES

Overview and Brainstorm of

Training StrategiesTony 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: Short stumps Bilateral involvement Physical limitation to hip muscular control Fear / decreased confidence

Reduce energy requirements

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…)

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.

2. Physical Potential (cont)

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: Polycentric. Respond to changes in velocity. Provide stability in stance phase:

Yield / shock absorption.Support body weight.

Shorten limb for foot clearance.

Types of Knees

Mechanical: Geometric locking. Hydraulic / pneumatic. Polycentric / single axis

Microprocessor controlled: Hydraulic Magnetorheologic

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!

Advantages

Kinematics / Kinetics: Flexion yield at weight

acceptance: (Sutherland 1997)

Shock absorptionNo 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

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)

Advantages

___normal

….4-bar

---Total knee

(Sutherland et al 1997)

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.

Advantages

___normal

….4-bar

---Total knee

(Sutherland et al 1997)

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)

Advantages

Flexion under load Hydraulic knees

More natural stand sit.Descent of ramps / stairs.

Advantages

Stumble recovery 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:

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 Beware of some tasks:

Forceful hyperextensionWalking / stepping backwardsStepping down backwards (off stool, ladder, etc)Foot position during some standing / reaching tasks.Loading forefoot with knee extended while on uneven

ground.

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.

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

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: 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… 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).

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.

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.