Evidence-based and biomechanical considerations
for selection of mechanical prosthetic knees
Andreas Kannenberg, MD PhD, Director Medical Affairs
| © Otto Bock HealthCare
Background
Importance 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
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Body of evidence on prosthetic knee selection
Mechanical prosthetic knees – 2 systematic reviews
van 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.
| © Otto Bock HealthCare
J Rehabil Res Dev 2004, 41 (4): 55-70
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Body of evidence on prosthetic knee selection
Mechanical prosthetic knees – 2 systematic reviews
Samuelsson 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,
| © Otto Bock HealthCare
and quality of life: a systematic review. Prosthet Orthot Int 2012, 36(2): 145-158
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Prosthetic knee selection
Do 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
Biomechanical considerations – Stance control
Knee flexion
under weight bearing
no
knee flexion
• locked knee
• friction brake knee
limited
knee flexion
• multiaxial knee (≥5 axes)
unlimited
knee flexion
• hydraulic knee
• bouncing adapter
• 4-bar polycentric knee
modified after: Blumentritt S: Biomechanical aspects of the indications of prosthetic knee joints.
Orthopädie-Technik 2004,55(6):508-524 (Article in German)
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Mechanical knee stability and function
A reciprocal relationship
Stability*
locked
knee
Function
friction brake
4-bar
multiaxial
hydraulic free single
knee
polycentric knee knee (≥5 axes) knee
axis knee
*Stability = prevention of knee collapse during level walking ( ≠ Safety !!! )
Safety = stability during level walking
+ stability during walking on uneven terrains, slopes, stairs
+ toe clearance
+ stumble recovery
modified after: Blumentritt S: Biomechanical aspects of the indications of prosthetic knee joints.
Orthopädie-Technik 2004,55(6):508-524 (Article in German)
| © Otto Bock HealthCare
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Locked knee
Benefit
 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
3R40
 does not support reciprocal gait (step-over-step) on uneven
3R41
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.
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Friction brake knee
Benefit
 able to flex during swing phase – more natural swing pattern and foot
clearance
Disadvantages
 requires full extension at heel strike
 no stance flexion for shock absorption
3R49/15, 3R42
 does not allow for knee flexion at late stance (pre-swing)
3R90 / 3R92
 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.
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4-bar polycentric knee
Benefit(s)
 usually very safe at heel strike
 shortening of calf during swing – improved foot clearance
3R36/20
 allows for knee flexion at late stance – more natural and dynamic gait pattern
 shortening of thigh during sitting – more natural appearance
Disadvantages
 requires full extension at heel strike
 no stance flexion for shock absorption
 does not support walking on uneven ground, slopes, and stairs
 information on centrode required to match knee and patient
3R78
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. | © Otto Bock HealthCare 10
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
Disadvantages
3R60 EBS / 3R60 EBSpro
 requires full extension at heel strike
 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. | © Otto Bock HealthCare 11
Hydraulic knee
Benefits
 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
Disadvantages
3R80
 requires full extension at heel strike
 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
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Hydraulic knee
Hydraulic knees are suitable for mobility grade 3 (unlimited
community) and 4 (very active [“athlete“]) ambulators only.
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Free single axis knee and very dynamic 4-bar knee
Benefits
 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
3R55
3R95
 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
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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.
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Prosthetic knee selection
Biomechanic al considerations – Swing control
Swing phase control
one (fixed) gait speed
low to medium range
of gait speeds
full spectrum
of gait speeds
Friction
Pneumatic
Hydraulic
Swing extension assist
if full extension prior to heel strike.cannot be
reached reliably
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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.
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Summary
Prosthetic knee selection
 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.
| © Otto Bock HealthCare
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Thank you
for your attention.
andreas.kannenberg@ottobock.de