1. Andreas Kannenberg, MD PhD, Director Medical Affairs
Evidence-based and biomechanical considerations for selection of mechanical prosthetic knees
Andreas Kannenberg, MD PhD, Director Medical Affairs

2. Importance of prosthetic knee selection
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:
provide the greatest safety possible during ambulation
support as many as possible activities of daily living

3. 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. J Rehabil Res Dev 2004, 41 (4): 55-70

4. 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, and quality of life: a systematic review. Prosthet Orthot Int 2012, 36(2):

5. 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

6. Prosthetic knee selection
Biomechanical considerations – Stance control
Knee flexion
under weight bearing 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
modified after: Blumentritt S: Biomechanical aspects of the indications of prosthetic knee joints. Orthopädie-Technik 2004,55(6): (Article in German)

7. Mechanical knee stability and function
A reciprocal relationship
Stability*
Function
locked knee
friction brake knee
4-bar polycentric knee
multiaxial knee (≥5 axes)
hydraulic knee
free single 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): (Article in German)

8. 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
does not support reciprocal gait (step-over-step) on uneven ground or slope and stair descent
3R40
3R41
Suitable for mobility grade 1 (household) ambulators or amputees who are not able to safely control a more functional knee only.

9. 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
does not allow for knee flexion at late stance (pre-swing)
does not support reciprocal gait on uneven ground or slope and stair descent
3R90 / 3R92
3R49/15, 3R42
Suitable for high mobility grade 1 (household) and low to medium mobility grade 2 (limited community) ambulators.

10. 4-bar polycentric knee
3R36/20
Benefit(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
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.

11. Multiaxial knee with ≥5 axes
3R60 EBS / 3R60 EBSpro
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
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.

12. 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
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
3R80

13. Hydraulic knee
Hydraulic knees are suitable for mobility grade 3 (unlimited community) and 4 (very active [“athlete“]) ambulators only.

14. 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
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
3R95
3R55

15. 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.

16. 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

17. 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.

18. Prosthetic knee selection
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.

19. Thank you
for your attention.