Evidence-based and biomechanical considerations for selection of mechanical prosthetic knees

| © Otto Bock HealthCare

Evidence-based and biomechanical considerations for selection of mechanical prosthetic kneesAndreas Kannenberg, MD PhD, Director Medical Affairs

| © Otto Bock HealthCare 2

BackgroundImportance of prosthetic knee selection

For transfemoral amputees selection of the most appropriate prosthetic

knee is key to successful rehabilitation and reintegration into social and

professional life.

The prosthetic knee must meet two essential needs:

1. provide the greatest safety possible during ambulation

2. support as many as possible activities of daily living


Body of evidence on prosthetic knee selectionMechanical prosthetic knees – 2 systematic reviewsvan der Linde et al. 2004

only 5 studies on mechanical prosthetic knees had good enough

quality to be included in the review

one study concluded that a Mauch SNS with a lock may enable

vascular amputees to adopt a higher walking speed as compared to

an unlocked knee unit

advanced swing phase control mechanisms (pneumatic or hydraulic)

may improve gait symmetry and velocity of active prosthesis users

van der Linde H, Hofstad CJ, Geurts ACH, Postema K, Geertzen JHB, van Limbeek J: A systematic review of the effect of different prosthetic components on human functioning with a a lower limb prosthesis. J Rehabil Res Dev 2004, 41 (4): 55-70


Body of evidence on prosthetic knee selectionMechanical prosthetic knees – 2 systematic reviewsSamuelsson et al. 2012

Systematic review of all studies in lower limb prosthetics

818 studies found

737 excluded as not pertinent or duplicates

73 studies excluded for poor quality

8 studies had sufficient methodological quality to be reviewed

Not a single study with mechanical prosthetic knees had enough

methodological quality to be included in the review.

Samuelsson KAM, Töytäri O, Salminen AL, Brandt Å: Effects of lower limb prosthesis on activity, participation, and quality of life: a systematic review. Prosthet Orthot Int 2012, 36(2): 145-158


Prosthetic knee selectionDo prosthetic knee classifications help?

Various knee classifications exist all are based on technologies used for stance and swing control

extensive background knowledge of features and functions of knee

technologies is needed

features and functions of prosthetic knees using the same technology

may differ remarkably

prosthetic knee classifications do not facilitate clinical decision

making

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Prosthetic knee selection

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Biomechanical considerations – Stance control

Knee flexion under weight bearing

modified after: Blumentritt S: Biomechanical aspects of the indications of prosthetic knee joints. Orthopädie-Technik 2004,55(6):508-524 (Article in German)

no knee flexion

limited knee flexion

unlimited knee flexion

• locked knee

• friction brake knee

•4-bar polycentric knee

•multiaxial knee (≥5 axes)

•bouncing adapter

•hydraulic knee


Mechanical knee stability and functionA reciprocal relationship

modified after: Blumentritt S: Biomechanical aspects of the indications of prosthetic knee joints. Orthopädie-Technik 2004,55(6):508-524 (Article in German)

Stability* Function

locked knee

friction brake knee

4-bar polycentric knee

multiaxial knee (≥5 axes)

hydraulic knee

*Stability = prevention of knee collapse during level walking

Safety = stability during level walking + stability during walking on uneven terrains, slopes, stairs + toe clearance + stumble recovery

( ≠ Safety !!! )

free single axis knee


Locked kneeBenefit total stability (prevention of knee collapse) at all times and circumstances

Disadvantages walking with a stiff prosthetic leg at all times

compensatory movements to produce foot clearance

no stance flexion for shock absorption

does not support reciprocal gait (step-over-step) on uneven

ground or slope and stair descent

Suitable for mobility grade 1 (household) ambulators or amputees who are not able to safely control

a more functional knee only.

3R40

3R41


Friction brake knee

Benefit able to flex during swing phase – more natural swing pattern and foot

clearance

Disadvantages requires full extension at heel strike


does not allow for knee flexion at late stance (pre-swing)

does not support reciprocal gait on uneven ground or slope and stair descent

Suitable for high mobility grade 1 (household) and low to medium mobility grade 2 (limited community) ambulators.

3R49/15, 3R423R90 / 3R92


4-bar polycentric kneeBenefit(s) usually very safe at heel strike

shortening of calf during swing – improved foot clearance

allows for knee flexion at late stance – more natural and dynamic gait pattern

shortening of thigh during sitting – more natural appearance



does not support walking on uneven ground, slopes, and stairs

information on centrode required to match knee and patient

4-bar knees with a safe centrode are suitable for medium to high mobility grade 2 (limited community) and mobility grade 3

(unlimited community) ambulators.

3R36/20

3R78


Multiaxial knee with ≥5 axes

Additional benefits to 4-bar knee may support limited stance flexion for shock absorption

may support walking on shallow slopes and sligthly

uneven ground


stance flexion of ≥5° requires stance extension dampening to prevent buckling

does not support reciprocal gait on heavily uneven ground or

steeper slope and stair descent

Multiaxial knees are suitable for medium to high mobility grade 2 (limited community) and mobility grade 3 (unlimited community)

ambulators who tolerate stance flexion.

3R60 EBS / 3R60 EBSpro


Hydraulic kneeBenefits may support stance flexion for shock absorption

may support loading for sitting down

may support reciprocal gait on uneven ground as well as slope

and stair descent


stance flexion of ≥5° requires stance extension dampening to prevent buckling

switch mechanism between stance and swing is susceptible to unintentional

switching – amputee must always be “alert“, prepared, and able to take over

control with residual limb or fall in a controlled manner

3R80


Hydraulic knee

Hydraulic knees are suitable for mobility grade 3 (unlimited

community) and 4 (very active [“athlete“]) ambulators only.


Free single axis knee and very dynamic 4-bar kneeBenefits full voluntary control of the prosthesis

may allow for (free swing) reciprocal gait on uneven ground

as well as slope and stair descent if properly motor controlled

by the residual limb

Disadvantages absolutely no safety features other than posterior offset of the knee or instant

center of rotation, respectively

requires full extension at heel strike

requires excellent residual limb strength and coordination to control and

secure the prosthesis at any times and circumstances as well as the ability

to fall in a controlled and “safe“ manner

3R953R55


Free single axis knee and very dynamic 4-bar knee

Free single axis and very dynamic 4-bar polycentric knees

are suitable for mobility grade 4 (very active [“athlete“])

ambulators only.


Prosthetic knee selectionBiomechanic al considerations – Swing control

Swing phase control

Friction Pneumatic Hydraulic

one (fixed) gait speed low to medium range of gait speeds

full spectrum of gait speeds

Swing extension assistif full extension prior to heel strike.cannot be

reached reliably


C-Leg research summary

14 clinical trials with 236 patients

12 biomechanical studies with 129 patients

5 patient surveys with 368 patients

3 health-economic studies with 146 patients in 3 countries

1 systematic review

The C-Leg combines excellent safety (not only stability) and support of function such as safe reciprocal gait

on uneven terrain and slope and stair descent.


Summary

Current clinical evidence and technical classifications don´t facilitate individual prosthetic knee selection.

Knee selection may be based on biomechanical considerations on certain stance and swing control features to be matched with the physical (and mental) capabilities as well as mobility needs of the amputee.

Manufacturers have to provide more detailed information on their prosthetic knees than they currently do on their websites, marketing materials, and instructions for use.

Manufacturers are summoned to initiate and support research with their prosthetic knees to produce clinical evidence to better guide individual clinical decision making.

Prosthetic knee selection

Thank you

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for your attention.

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Evidence-based and biomechanical considerations for selection of mechanical prosthetic knees