Lecture 10
Dimitar Stefanov
LOWER-EXTREMITY PROSTHESES
Example
socket
(individually fitted component)
residual limb (soft tissue and bones)
In case of partial amputation, inserts within a conventional
shoe are can be applied.
Energy-stored feet.
In general, it is realized via flexible keel, which provides non-linear spring action
similar to the push-off phase of walking or running.
DYNAMIC RESPONSE FEET
The distinguishing characteristic of this
group is a plastic spring mechanism in
the keel which deflects during heel off
and returns to its resting position during
toe off. Often called "energy storing" by
manufacturers, these feet provide a
subjective sense of push-off for the
wearer, a more normal range of
motion, and a more symmetric gait.
SINGLE-AXIS FOOT
Single axis solid ankle cushioned heel (SACH) prosthetic foot – provides
planar flexion and smooth transition to mid-stance; increased knee stability;
best suited for short-term use, such as on preparatory devices or for elders who
may walk with a shuffling gait and never fully load the forefoot.
In case of partial amputation, inserts within a conventional
shoe are can be applied.
Energy-stored feet.
In general, it is realized via flexible keel, which provides non-linear spring action
similar to the push-off phase of walking or running.
DYNAMIC RESPONSE FEET
The distinguishing characteristic of this
group is a plastic spring mechanism in
the keel which deflects during heel off
and returns to its resting position during
toe off. Often called "energy storing" by
manufacturers, these feet provide a
subjective sense of push-off for the
wearer, a more normal range of
motion, and a more symmetric gait.
SINGLE-AXIS FOOT
Single axis solid ankle cushioned heel (SACH) prosthetic foot – provides
planar flexion and smooth transition to mid-stance; increased knee stability;
best suited for short-term use, such as on preparatory devices or for elders who
may walk with a shuffling gait and never fully load the forefoot.
Multi-axis foot
Swim prostheses
The Jaipur foot
•inexpensive prosthetic foot – India
•Made of vulcanized rubber
•Wooden keel
•Consists of three inserts: fore-foot and heel of micro cellular rubber
and an ankle of laminated wood
•Flexibility in three planes
•Well suited for walking over uneven terrain, climbing trees, etc.
Below-the-knee prosthesis
Important problems:
•design of convenient socket; prevention of pistoning;
•reduction the forces on the residual limb;
•large contact area between the distal end of the limb and the
socket.
•Suspension through latex rubber sleeves and a waist belt
attached to a cuff.
•CAD-CAM design can be applied in the socket production.
• The wire-frame model representation of the socket should
be viewed by the prosthetist and modified.
Above-the-knee prostheses
Knee joint – much important component
It should be lightweight and safe in operation.
Design solutions of knee joint:
A./ Simple mechanical device with manually operated locking mechanism.
Disadvantages:
•Low functionality
•useful for sitting only
•doesn’t allow bending during the swing phase.
B./ Mechanical devices that allow knee to flex when it is unweighed and
which lock when a weight threshold is exceeded. Solutions for activation of
the knee lock:
•Pressure of the heel
•Ankle flexion
C./ Hydraulic knees –
•They allow stance and swing phase control; Adjustment
of the swing phase to suit to individual’s pattern of
walking.
•Hydraulic resistance to flexion;
•Lock of the knee joint in hyperextension;
•Unlock the joint when the forces to the prosthetic forefoot
exceed a threshold;
•Manual lock for activities which require maximal stability
(driving an automobile, standing on a bus, vocational
activities);
•Release for maximum flexibility.
Solutions:
•Piston and a hydraulic cylinder.
•The cylinder is perforated to allow fluid to flow from
one side of the cylinder to the opposite side when the
piston moves.
•The distribution of the holes within the cylinder
determines the amount of damping.
•Hydraulic cylinder and piston.
• Holes on the cylinder ends and electromagnetcontrolled valve which determine the fluid flow.
•Microprocessor control unit and a hall-effect sensor
for knee-bending measurement.
Otto-Bock knee prostheses:
3R45 Modular Knee Joint
An optimal gait pattern is
achieved by adjusting the
independent swing phase
flexion and extension
resistances
integrated miniature
hydraulic cylinder
3R80 Modular Rotary Hydraulic
Knee Joint
•Weight activated;
•Cadence responsive;
•Precise adjustability;
•135 degree flexion angle;
•Independently adjustable
hydraulic flexion and extension
resistance.
•Pneumatic
cylinder and a
swing-phase
controller.
The Endolite intelligent prosthesis
•Swing-phase controller
(control in different
cadences)
•4-bit microprocessor
which controls a needle
valve, via a stepper motor
•The controller is
programmed (by the
prosthetist) to provide an
optimal damping in
different walking patterns.
Prosthetic gait analysis and assessment
Harmless prostheses design – to minimize the risk of injury associated
with stumbling, slipping and falling.
•Prosthethic limbs do not provide direct proprioceptive feedback.
•Some force information is transferred to the user via the socket.
•Often prostheses produce sound or vibrations that change with the force and
cadence.
People with lower-limb prostheses use a higher oxygen consumption, which
varies to the different model prostheses.
gait analysis, force-reactions measurement.
Biomechanical techniques for assessment the adaptation of the user to
the lower-limb prostheses:
Lower-extremity orthoses
Applied in case of lower limb paralysis
Orthosis design:
•The ankle is treated as a joint with a single DOF
•The knee joint is modeled with two DOF joint (flexion/extension
in the sagital plane and rotation in the transverse plane)
•The hip is modeled with a joint with 3 DOF
(abduction/adduction in the frontal plane, flexion/extension in the
sagital plane, and internal/external rotation).
Mechanically strong – static and dynamic loads.
Walking stability and prevention of falling.
The sensory feedback to the user contributes the stability increase.
Ankle-foot orthosis
Designed of molded plastic or metal
Foot design – very important (heel high)
Mechanical ankle-foot orthosis
Vanini-Rizzoli Stabilizing Limb Orthosis (VRSLO)
The polypropylene orthosis is inserted into a
specially designed leather boot.
The insole of the orthosis is angled to provide
10 to 15 degrees of planar flexion.
•Attempt for development of lightweight, simple and easy
to use otthosis.
Knee-ankle-foot orthoses –very high energy-costs during
use due to poor biomechanical efficiency.
Heavy, bulky, and bad
cosmetically looking
Three classes devices for movement of paralyzed legs:
•Purely mechanical orthoses
•Hybrid devices (mechanical support + FES)
•FES alone.