Dynamic response foot

DYNAMIC RESPONSE
FOOT
DIBYA RANJAN SWAIN
MPO 1st year
SVNIRTAR

INDEX:
1. Human feet and its function
2. Prosthetic foot and its classification
3. Dynamic response foot
4. History
5. Components
6. Factors for selection of DRF
7. Biomechanics
8. Classification of dynamic response foot
9. Pros and cons
10.Controversies
11.Conclusion

HUMAN FEET AND ITS FUNCTIONS:
 The feet are the flexible structures
of bones, joints, muscles, and soft
tissues that let us stand upright
and perform activities like walking,
running and jumping.
 Muscles, tendons and ligaments
that run beneath surface of the
feet allow complex movements
needed for motion and balance.
 It produces balance and
propulsion along with providing
foundation for the rest of the body.

PROSTHETIC FOOT:
The primary purpose of prosthetic foot is to serve in place of
anatomic foot and ankle.
The function of prosthetic foot and ankle unit is to allow smooth
and natural transition of the body during walking.
Functions:
 Joint simulation
 Shock absorption
 A stable weight bearing BOS
 Muscle simulation
 A pleasing appearance

CLASSIFICATION
 STRUCTURALLY:
F00T
ARTICULATED
SINGLE-
AXIS
MULTI-
AXIS
NON-
ARTICULATED

FUNCTIONALLY
CONVENTIONAL FLEXIBLE KEEL
DYNAMIC
RESPONSE
MICROPROCE
SSOR
CONTROL
HYBRID
DESIGNS
FOOT

DYNAMIC RESPONSE FOOT
INTRODUCTION:
 Dynamic Response Foot stores and
releases energy with ambulation.
 They function as sophisticated
springs that cushion at initial
contact and provide propulsion at
terminal stance, enhancing the
ability to walk long distances, run ,
and jump.
 Individuals with more-active
lifestyles require dynamic response
feet.

COMMON FEATURES :
 Good shock absorption during heel strike.
 Dynamic roll over action during ambulation.
 Elastic axial compression under load.
 Compensation for uneven walking surfaces.
 Flexible restoring force of the forefoot during fast
walking and running.
 Pleasing cosmetic appearance.

HISTORY
 Initially, the conventional foots like
SACH foot, single axis foot etc.
were used adversely for most of
the amputees besides of the
activity level and interest.
 Mainly amputees having athletic
lifestyle had no other options.
 As the conventional designs were
too stiff to permit comfortable
ambulation at more then a
moderate pace for high level
activities and similar recreational
activities.

Finally, in 1984 American inventor
Van Philips introduced first ever
dynamic response foot as Flex foot.
He( born in 1954) lost his leg below
the knee at the age of 21 who was an
athlete himself.
For a young and active individual the
options were stiff and uncomfortable.
So, he ultimately created a foot made
from carbon fiber which stored kinetic
energy from wearers steps as potential
energy, like a spring.

FACTORS FOR SELECTING DYNAMIC
RESPONSE FOOT:
 Amputation level
 Age
 Weight
 Foot size
 Activity level
 Economical conditions
 Environmental conditions
 Occupation
 Goals and recreational activities

 Amputation level:
- There is no certain limitations according to the length of the stump as long
as the lower limb muscles are strong and give a good range of motion.
- For ankle disarticulation (symes) specially designed foots are present in
the form of low profile DRF
- For partial foot amputations only carbon fiber foot plates are present but
they don’t come under DRF
- For specific high energy sports with strong demands, different types of
dynamic response foot are present along with specified keels.

 Age:
- Mainly for adults are specified with high
energy activities who need unrestricted
foot motion
for those who want not just standing
and compromised walking, as after
certain age the muscles weaken which
cannot controlled the energy given off
by the foot.
- But, people with very good musculature
and strength who easily don’t
compromise with the age, use this foot
in a very sufficient manner.

 Weight
- Specific weight is also considered for using dynamic
response foot as the spring are used where they can
provide a balanced push off at an optimum shape and
position as well as transforming the body weight to the
ground.
- If weight is too much, the push off will not be enough
- If weight is less, the compression will not be enough
- The ideal weight is specific for different designs

 Foot size: according to the measurements
 Activity level:

 Economical conditions: surely the dynamic response feet
are expensive then the conventional designs but there
are so many variables that can be accepted by amputees
with different economical conditions.
 Environmental conditions: these kind foot are mainly
designed for athletic activities so good for smooth as well
as uneven and inclined surfaces but show some laxicity
in muddy, sandy and humid environments.

 Occupation:
for persons with official or other lower activity level
occupation this foot is not ideal.
having occupations were activity level is k3 and k4,
the dynamic response foot provides great support.

STRUCTURAL MECHANISM OF DRF
 Hybridizing the properties of different classes,
primarily by combining dynamic response feet with
multi-axis attributes.
 The traditional classification system has become
outdated.
 Proposed subsets could include:
 Forefoot keel
 Heel lever
 Hind-foot roller
 Flexing strut
 Forefoot inversion/eversion
 Multi-axis hind foot
 Integrated shock

 Forefoot keel
 The forefoot keel is characteristic of the
most basic ESAR foot/ankle mechanism
with any number of materials and
configurations.
 The forefoot keel can be a single-bladed
member or consist of multiple separate
members.
 Stiffness is directly dependent on the
cross-section, material, keel length, and
geometry.
 Some designs use multiple layers that
collapse progressively.
 Others use a urethane sandwich, which
has a smoothing effect on the load
progression.

 Heel lever
 The heel lever emulates the heel rocker,
which contributes to load acceptance and
ankle plantar flexion characteristics.
 Many foot/ankle mechanisms simply use a
cushion heel that simulates plantar flexion
by compression.
 Such as flexfoot, a heel lever projects
posteriorly from the forefoot keel or midfoot
attachment, and often provides stiffer
support than a cushion heel.
 Recent designs have used multiple levers,
linkages, urethane bumpers or a urethane
sandwich to simulate the progressive
stiffness of the anatomical foot and ankkle.

 Hind foot roller
 A hind foot roller mechanism used by many
foot/ankle mechanism uses a rocker
element mounted on a footplate to
approximate the ankle rocker from loading
response to mid-stance.
 This mechanism emphasizes the rotary
motion of the ankle rocker to ease the
transition from loading response.
 When configured as a complete circular
mechanism that wraps superiorly, the hind-
foot roller can also function indirectly in
shock absorption by emulating mid-tarsal
dorsiflexion. Excessive rocker function in
late mid stance would be non-physiologic,
leading to a loss of support in late stance.

 Flexing strut
 A flexing strut proximal socket attachment
originated with the flex-foot design.
 Incorporate the forefoot keel in one
integrated structure.
 The strut is usually a wide rectangular
cross section.
 Using continuous fibers in the strut
composition insures maximum flexibility
and strength.
 All these flexing strut designs offer the
greatest amount of energy return.
 The longer the continuous fibers are in the
lay-up of the composite, the greater the
amount of bending flexion that can occur.

 Forefoot Inversion-Eversion
 Forefoot inversion-eversion split-toe
design.
 Other designs are more integrated,
molding different durometer materials
or members together within the foot, so
there are not necessarily articulating
parts.
 Some designs create a forefoot
composite urethane sandwich.
 The damping characteristics of the fore
foot may limit the desired energy
return.

 Multi-axis hind foot
 A multi-axis hind foot as an articulating
component with urethane rubber
bumpers, bushings, spherical snubbers,
large rings to dampen motion.
 Separate modular ankle unit that can be
used with a variety of prosthetic feet, or it
may be integrated into the foot/ankle
mechanism itself.
 Multi-axis articulating designs often need
regular maintenance and servicing.
 Some variants extend the urethane
sandwich from the forefoot to the hind
foot.

 Integrated shock absorbers
 It incorporates shock absorbers in
parallel or series configuration.
 A series confg. Is usually found with a
damper more proximal to the spring-like
foot.
 A parallel design has a damper and
spring at same level.
 The telescoping nature of many shock
absorbers considered non-physiologic.
 Design will be able to provide more
variable stiffness or flexibility
characteristics.
 Future components are sure to continue
this blending of qualities to provide
greater foot function and movement.
Absorbers in
series
Absorbers in
parallel

FUNCTIONAL MECHANISM OF DRF
During the gait cycle,
1.At heel strike,
 The dorsi-flexion movement of the foot
allows the keel to compress or distort
 The keel which acts as a spring( leaf
spring or coiled spring), absorbs kinetic
energy.
 Helps in shock absorption

2.During mid-stance,
 the kinetic energy is converted in static
energy there by giving stability and balance
to the body weight.
 Inversion and eversion is simulated by
flexibility of the keel and some designs also
have split in the middle to accommodate it.
 As the tibia or the shin starts to advance,
the keel begins to bend and foot starts to
dorsiflex.

3.During heel off,
 As the dorsiflexion advances, the energy again transforms and aids
in forward propelling.
 The heel rise is controlled by the stiffness of the keel and when
weight is transformed onto forefoot, the keel extends all the way to
the toe area.
 The flexible keel eliminates the need for rocker effect and provides a
smooth roll over.
 Gives the wearer a subjective sense of push off in pre-swing
 Helps in the initiation of the swing phase
 Gives the fine trajectory to the foot during swing phase.

 The shank and foot deflection pieces are linked using spectralon fibers,
which holds them at their shortest length and the system is able to retain the
foots absorbed energy.
 By attaching the deflexion plates around the axle, the system ensures the
linear GRF is converted to the torque.
 while the lower plate controls energy during normal to moderate walking and
jogging
 the upper deflection plate resists the torque and absorbs energy during high
level activities like running etc and helps the foot to return to equilibrium after
each successive step.

ANATOMICAL FOOT
The PF and DF of the foot is
carried out by specific group of
muscles and are also controlled
by antagonistic group of
muscles in very controlled
manner.
CONVENTIONAL DRF
There are mainly 2 deflection
plates, the lower one controlls
the foot during normal to
moderate activies and the
upper one specially controlls
the lower plate during
vigorous activities as an
antagonistic muscle group.
ADVANCED DRF
Here, along with the
deflection plates, extra
components are added
like bumpers, cylinders
and electrical motors
which control the higher
torques more efficiently.
HIGHER PROFILE
DRF
These designs only
depend upon the
stiffness of blade and
the architechture( C &
J) to controll the torque.

CLASSIFICATION OF DYNAMIC RESPONSE FOOT:
Dynamic
response
foot
EARLY DRF ARTICULATED
DRF
ADVANCED
DRF

EARLY DRF DESIGNS:
 Flex foot:
 The first dynamic response foot
invented by Van Philips in1984.
made from carbon fiber with leaf
spring design.
 It is a long keel design where the
foot is directly attached to the socket
or to the knee portion of the
prosthesis.
 It requires sufficient space between
residuum and floor.

 The shock absorbing function of the carbon fiber
along with active heel reduces the stress on the
proximal joints, the knee, the hips and the spine
while walking or participating in higher impact
activities.
 The full length keel permits flex foot users to spend
equal time on their prosthetic and sound limbs,
enabling a full length step eliminating drop off.

Flex foot cheetah:
 Following the design of flex foot, in 1996 flex foot
cheetah was created also by Van Philips under
Ossur.
 About 90% of the athletes in Paralympics wear
flex foot cheetah and variations. It have been
worn by Oscar Pistorius and other athletes.
 Made from carbon fiber along with epoxy
polymer.
The blade is a combination of 30 to 90 layered
sheets of carbon fiber depending upon the weight
of the person which reduces air bubbles that can
cause breaks

 Seattle foot:
o Seattle foot was introduced by 1981 in a course
organized by American Orthopaedic Association.
o The main concept of the foot is to stores energy
at the initial part of the stance phase and
releases the same at push off.
o The keel is made up of Derlin like a multileaf
automobile suspension spring with anterior
deflection plate.
o This is the 1st energy storing foot and
commercial production strated in october 1985.
 Materials Used:
o Derlin
o Kevlor toe pad
o PU foam shell

 Springlite Foot:
 The Springlite foot is simmilar in design
to the flex foot and consists of two layers
of carbon and fiberglass filaments
surrounded by a soft cover.
 Indication:
 Vigorous sports activity
 Advantages:
 Light weight
 Allowed vertical jumping.
 Provides med. And lat. Stability
 Symes and pedeatric models are
avaliable.

 Sabolich foot:
- Developed by John Sabolich of Sabolich
prosthetic center, Oklahoma.
- The foot design resembles the human
anatomy of the longitudinal arch with a
bridge like structure fabricated from Delrin.
- During heel contact the energy is stored as
the person progresses to foot flat during
mid-stance the arch is flattened again and
energy is released later in the gait cycle.
- This assists in propelling the CG up and
forward.
- The foot is custom manufactured according
to the activity level and weight appropriate
for the amputee.

 Carbon copy ll:
- Mauch laboratory with Ohio willow
wood designed a foot shell for
mauch hydraulic ankle unit. With
engineered carbon composite keel
they released carbon copy I.
- But, after further development,
carbon copy II was the first
cosmetically appealing energy
storing foot brought to market.

- The keel is composed of two strong deflection
plates, made out of carbon graphite plate.
- The longer deflection plate terminate at the distal
IP joint.
- Shorter upper plate is activated under high load.
- Plates are available in 3 levels of resistance.
Provides little medio-lateral stability.

 Quantum foot:
- it was introduced in September 1988 by
Hanger.
- The keel is in the form of spring module
consisting of a lower and upper deflection
plates attached to ankle base from where
the plates project forward to the MTP joints
and backward to the heel.
- The lower plate stores and returns energy
during last half of the stance phase.
- The upper plate acts as a spring in case of
high forces .

 C-walk:
- A new generation innovative design made from
carbon composite dynamic response foot which
provides walking at different speeds, walking uphill
or down heel with a secure feeling and harmonious
roll over on uneven grounds.
- It consists of,
C-spring(coiled)
Base spring
Control ring
Heel elements

PROPERTIES:
o Large controlled PF up to 12degrees
o Multi axis motion for uneven surfaces
o Reduced strain on sound leg
o Cushioned heel strike
o Physiological rollover
o Harmonious transition from stance to swing
o Comfortable walking uphill and down hill.

 ARTICULATED designs:
-These feet are the combination of multi-axial ankle with a
dynamic response foot, in an effort to offer the
advantages of both concepts.
 Total concept foot:
-Developed by OSSURE, Sweden
-Provides 10 degree DF to 25 degree PF
-Heel height from 0-2 inches

 Advanced DESIGNS:
 College park true step foot:
- It designed to mimic the anatomic
foot and ankle.
- It contains,
1.PF and DF bumpers
2.Ankle alignment bushings
3.The bumpers are easily
changed to accommodate variable
weights, thereby providing the
correct resistance for smooth gait.

 Luxon max foot:
- It incorporates computerized knee or c-
leg
 Pathfinder foot:
- It combines with adjustable pneumatic
heel spring with two carbon fiber
springs for dynamic response.
 Proprio foot:
- An adaptive microprocessor controlled
ankle
- Have different types of modes
- Weatherproof
- Controlled by smart application

COMPARISON OF PROSTHETIC FOOT
PROSTHETIC
FOOT
INDICATION ADVANTAGES DISADVANTAGES PICTURES
Single axis  Enhances
the knee
stability
K1
 Adjustable
bumpers
 Rapid PF
 Increased wt
 Non cosmetic
 Debris can enter
the jt.
Multi axis  Accommo
dates
uneven
surfaces
K2
 Allows
multidirection
al motion
 Good shock
absorption
 Increased wt
 Less stability on
smooth surfaces
SACH foot  General
use
K1 K2
 Large variety
of heels
 Reliable
 Less
maintenance
 Limited
dorsiflexion due
to rigid keel
 No propulsion at
terminal stance.

CONTD
Flex foot  Vigorous
sports
K3 K4
 Light wt
 Vertical
jumping
 Med-lat
stability
 high cost
 Complex
fabrication and
alignment
 Difficulties in
hell height
changes
Spring-lite foot  Same as
flex foot
K3 K4
 Same as flex
but less
expensive
 Same as flex
Seattle foot  General
sports
 Active
wearer
K3 K4
 Dynamic
response
improves
cosmetic
appearance
 Increased
weight

CONTD
Carbon copy
II
 Active
wearer
 Smooth
stance roll
over
K3 K4
 Good med-
lat stability
 Light weight
 Increased
cost
College park
true step
 High
activity
level
K3 K4
 Increased
stability
 Adjustable
bumpers
 Increased
maintenance
 Expense
 Avl only for
adult sizes
and low
heeled shoes
C- Walk  High
activity
level
 Active
patient
K3 K4
 Large
controlled
PF up to
12degrees
 Increased
maintenance
 Expense
 Increased wt

CONTROVERSIES:
Do dynamic response foot give the athletes some kind of unfair
advantages?
 In 1980s, initially a J-shaped foot was introduced
which was build out of stiff carbon fiber meant to
imitate the strength and springiness of the
anatomical calf-muscles with flexible-deep-firm
fitting socket to minimize energy loss.
 Then Ossure, get rid-off the heel spring making it
fully j shaped with increased stiffness and came out
with flex sprint.

 IFAA- international federation of athletic
association, changed the rule:
‘Use of any devices that incorporates springs,
wheels or any other element that provides the user
with an advantage over another athlete not using
such device is not permissible’.
 But, runners with prosthetics run differently than able
bodied runners.
 Then, a group of German researchers worked with
Oscar Pistorius analyzed that,
 Prosthetic DRF store and release energy more
efficiently then actual anatomical muscles.

 But, they did not measured any metabolic factors like
heart rate, oxygen consumption etc.
 It was based only on kinetic factors.
 Again, researchers of RICE university did a follow-up
study focused on metabolic factors performed with
both types of runners and came out that;
 Yes, the prosthetic foot gives different mechanics but
does not gives physiologic edge which the Germans
predicted.
 This study ruled IFAA decision, and allowed Oscar
Pisturious to run in the events.

 Study on, running economy with heart rate
response showed that;
running with prosthetic foot is better in
everything due the groundbreaking change in the
design of foot.

 Again, in 2018 studies showed that, as the angle
of impact increases, the stiffness in the spring
decreases.
 Which gave rise to a new question,
Does different designs give more advantage
then others?
 As a result which again AFAA announced,

New studies with bilateral trans-tibial amputees
variations like, different models, height, stiffness and
shape found that,
The only thing that influenced speed is, the shape
of the blade.

CONCLUSION:
By February 2020,
IFAA still not allows to use any such devices. But,
Able and disable runners have different
biomechanics
The disable runners compromise in physiology
Mostly all the studies are based on small sample
sizes as its difficult to get specific samples
 the future goal of the athletes still counts on.

REFERENCES
 A publication of the amputee coalition of america in
partnership with the U.S Army Amputee patient care
and programme.
 Michelle M. Lucardi, Orthotics and Prosthetics in
rehabilitation, 2nd edition, 422
 Perry J. Gait Analysis ; Normal and Pathological
function. New York, Mcgraw-Hill,1992, 11-16.
 www.collegepark.in
 www.ottobock.com
 www.endoliteindia.in

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