PROSTHESIS FOR HIP DISARTICULATION AMPUTEES - STUDY

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PROSTHETICS
• A Hip-Disarticulation consist of the removal of the
entire leg at the hip joint and results in the loss of 3
major limb joints: The ankle, the knee and the hip
joint
• Douglas G. Smith, MD comments in an article
in the magazine In-Motion: …
“Trying to overcome the loss of three weight-bearing joints, rather
than one or two, is extremely complicated. Living with a
transfemoral amputation is about 10 times as tough as living with a
transtibial amputation, and living with a hip- or pelvic-level
amputation is perhaps 100 times harder. Walking, standing, and
even sitting balance – something that most of us take for granted –
are greatly affected by amputations at the hip or pelvis”

PROSTHETICS
1. Malignant musculoskeletal tumors (most often in younger patients)
2. Limb ischemia (perivascular disease and complications to diabetes)
3. Trauma (such severe traumas often result in the death of the
patient)
4. Severe lower limbs infections (chronic skin or bone infection)
As a result. . . . . . .

PROSTHETICS
• Most prosthetist have little experience with this type of amputation
• Only 20% of hip amputees use a prosthetic leg full-time (i.e. 8 to 12
hr./day)
• From these 20%, only a small minority use a prosthetic leg without a
cane or crutch
• This small minority of full time users without walking aids consists
primarily of the young patients with malignant tumors.
• There is a persistent belief within the medical community that most
middle aged hip-disarticulation amputees will ambulate with crutches
or a wheelchair only!!!
* Consent is is a bit of a misnomer as I had to choose between 1) hip-disarticulation or 2) slowly dying from infection or 3) slowly dying from the I.V. Vancomycin (antibiotic of last resort) eating my body away.
I REMEMBER CLEARLY THE SURGEON EXPLAINING TO ME, AS I WAS SIGNING THE CONSENT* PAPERS PRIOR
TO THE SURGICAL PROCEDURE, THAT I WAS GOING TO SPEND THE REST OF MY LIFE ON CRUTCHES

PROSTHETICS
• I am not an athlete (165lbs/5’11”), and certainly not young (52+),
yet…..
• I am a full-time user AND I walk without a cane and…
• I live a full life and do just about everything I want.
• Granted, there are some limitations. Yes, I can’t play tennis anymore.
Big deal! Yes, I can’t ride motorcycles anymore. That, I do miss indeed
but it’s not the end of the world.
• Is the prosthesis comfortable? Hell no! But it beats using crutches all
day.
• Biggest problem with using crutches is that we loose the use of our
hands. People are always surprised when I say this. What I mean is
that we cannot carry things easily when using crutches.

PROSTHETICS
• The key to success is to become deeply involved in the process.
• It is easy to believe that “This is as best as it can be!”. These highly trained professional
prosthetists have done their best but I still can’t walk with the damn’ leg. It hurts, I keep
on falling (This I did. 3 broken wrists, 1 rib…). Therefore, I must be the problem. I am not
just good enough. I am too old. I am not trying hard enough. I am too weak, etc…
• True! This highly trained professionals try hard but…
• They lack experience in this domain.
• They don’t have the time to do it right and,
• These types of prosthetic legs are finicky to set up. It takes days of incremental
adjustments to get it just right. (i.e. Efficient to use (not tiring) and stable)
• For example, on my current leg, there are 44 set-screws and other
adjustments, all interacting with each other, altering the geometry and other
parameters of the leg.

PROSTHETICS - SOCKET
• The first socket was a disaster. Eventually, my prosthetist relented and accepted to build a second
one at no cost. Including many modifications I had suggested during numerous discussions.
• This socket is much better but by no mean GOOD.
• From what I have read in several technical articles, it could be much better.
• The problem consist of:
• 1) Finding a prosthetist, that actually knows what he is talking about. Not so easy, as they all claim to
be experts….
• 2) COST. For most non amputees, it is always a surprise. A socket cost around $12,000! (Yes, you are
reading right!) and, the icing on the cake is… MOST insurances do not pay at all, or pay only a minor
fraction of the cost. Prosthetics are included in insurance contracts under durable medical
equipment*. YES, it is covered but maximum payment is limited to……. $2,000/year. Nobody check
these things unless… they lose a limb.
*BTW: I wish they were durable. I have yet to find a knee that last more than 2 years!!

PROSTHETICS - SOCKET
Side View Back View
Carbon Fiber Socket
Deep recesses over the iliac crest
provides positive support, limiting
“pumping” and increasing toe
clearance (my idea)
Otto Bock 7E7 hip
joint (titanium)
Triple ski-boots type ratchets and
straps providing a TIGHT fit of the
socket around the pelvis for
improved “feel” and control
Non stretchable heavy duty
straps preventing change in
socket geometry with time
Note: I did the strapping system and ratchet buckles. The dimensions
of the straps are critical in maintaining the proper shape of the socket.
Earlier system used fabric straps that used to stretch over time.

PROSTHETIC COMPONENTS
The cost of prosthetic components is just astronomical
A typical knee will cost between $10,000 and $30,000
A “computerized” knee between $30,000 and $40,000
A foot between $2,000 and $5,000
A typical pyramid adapter $400 (Al) or $800 (Ti)

2014 CHEVROLET MALIBU
Incredibly complex machine with thousands of parts. The
results of a century of research in advanced materials and
complex alloys with cutting edge electronics and
unparalleled durability with minimum service. 4-cylinder
2-liter 259HP turbocharged engine, 6 speed automatic
transmission, curb weight 3,547lbs
$30,000
TEH-LIN Knee
GRAPHLITE frame
ENDOLITE hydraulics
A few bits or carbon fiber
A handful of ball bearings
A simple hydraulic cylinder
Curb weigh 5lbs
MAKE SENSE DOESN’T IT?

HD PROSTHESIS
The first challenge with a hip disarticulation
(HD) prosthetic leg is:
WHERE TO LOCATE THE HIP JOINT?
The Canadian-Type HD prosthesis was
developed in 1954. The hip joint is located
on the front of the socket. It is connected
to the knee joint with an angled tube in
such a way that the axis of the knee is
posterior to the single equivalent force.
Single Equivalent Force
(~Projection of CG)

HD PROSTHESIS
Single Equivalent Force
(Projection of CG)
Knee Axis

HD PROSTHESIS
Knee Joint
Knee Axis
SEF
The knee axis is posterior to
the SEF line. The resulting
moments will force the knee
to bend in the direction
indicated by the arrows.
However, the knee is already
fully extended and cannot
extend further.
THE KNEE IS STABLE
1
2
3

HD PROSTHESIS
The SEF line is posterior to
the knee axis. The resulting
moments will force the knee
to bend in the direction
indicated by the arrows.
1
The knee will buckle under
load.
2
THE KNEE IS UNSTABLE3
Knee Joint
Knee Axis
SEF
ALIGNMENT is the process of
setting up the geometry of the leg

THE BIOMECAHNICS OF AN HD PROSTHESIS*
* From Charles W. Radcliffe
Note that at heel strike
the knee is almost
unstable. AK amputees
use their extensor
muscles to increase
stability. HD amputees
CAN’T!!
SEF posterior to
knee axis. The knee
bends.
Bump stop in hip
joint helps bending
the knee

Hip Joint (Ti)
Male/female pyramid
Adapter to refine hip/knee
Geometry (Ti)
Angled pyramid adapter (15°) (Ti)
Knee rotator
(Critical for driving)
Sliding adapter (Ti)
GRAPHLITE/ENDOLITE
Single Axis Knee Height adjustable
adapter (Ti)
OSSUR Flex Foot
(Carbon Fiber)

Hip Joint (Ti)
Male/female pyramid
Adapter to refine hip/knee
Geometry (Ti)
Knee rotator
GRAPHLITE/ENDOLITE
Single Axis Knee Height adjustable
adapter (Ti)
OSSUR Flex Foot
(Carbon Fiber)
Single axis knees are not recommended for HD prosthesis. True but,
A WELL ALIGNED single axis knee works very well in an HD prosthesis

Pylon (al)
Knee rotator
Offset adapter (Ti)
THE-LIN 5-BAR KNEE CARBON Pylon
with Ti adapter
Carbon Shock Absorber
OSSUR Reflex VSP
Foot
HD Prosthesis using the TEH-LIN TGK-5PSO Polycentric 5-Bar
Pneumatic knee with adjustable centroid

L
l
HD – TOE CLEARANCE
KNEE JOINT
FOOT
GROUND FLOOR
T

KNEE JOINT
FOOT
GROUND FLOOR
T
T = R-L
𝑻 = 𝒍 𝟐 + 𝑳 𝟐 − 𝑳
Toe Clearance T
Toe clearance is always an issue for all above knee
(AK) amputees and a very big issue for HD
amputees.
If the toes hit the floor during the swing phase, the
knee may not lock at heel strike and buckle under
load, resulting in a fall.
AK amputees have good control of their prosthetic
knee and the interface socket/stump provides
enhanced proprioception. HD amputees do not!
To minimize such event, it is customary to shorten
the prosthetic leg. However, this results in a non
symmetrical gait and pronounced limp.

One way to minimize the toe clearance is to
increase L.
The graph shows that by increasing L by
200mm, we gain 8mm of toe clearance. That
may not sound a lot but I can clearly feel a
change of 1 or 2mm in length.
However, for practical and cosmetic reasons,
we want the prosthetic knee to be at the
same level as the “good” knee and for the
same reasons we want the prosthetic foot to
be the same size as the good foot.
18
20
22
24
26
28
30
500 520 540 560 580 600 620 640 660 680 700
C(mm)
L (mm)
Clearance C as a function of L C
l=170mm
L=500-700mm
SO, WHAT DO WE DO?

THE POLYCENTRIC KNEE
All polycentric knees commercially available are 4-bar designs.
The “5-bar” knees are 4-bar knees with adjustable geometry.
In the 4-bar linkage A-B, C-D, the rotation center of the segment
B-D relative to A-C is located at the intersection the lines passing
through A-B and B-D. This virtual center of rotation is called
the centroid (or centrode by the O&P community)
l=170mm
L>500mm
Centroid
Centroid
Trajectory
The centroid is not fixed but is a function of the angle of
the knee. Note that the centroid moves in the vertical
direction AND in the posterior/anterior direction. This has
important consequences in term of alignment and
stability.
The polycentric knee allows to increase the distance L
without moving the knee. It is possible to gain up to
10mm in toe clearance with some polycentric knees.

T
KNEE JOINT
FOOT
GROUND FLOOR
T = R-L
𝑻 = 𝒍 𝟐 + 𝑳 𝟐 − 𝑳
Toe Clearance T
We need to build a foot/shin/knee
assembly in such a way that the toes
will rise in the final phase of the
swing.
Between α = 0 and α = α 1 , β < 90°
For α > α 1 β = 90°
β = 90° under load
Or, we move the foot!
α
α1
β=90°

Such a knee/foot system exists. PROTEOR, a French
manufacturer developed such system: The 1P50R
Hydracadence II.
Unfortunately, PROTEOR is poorly distributed in the US.
Nevertheless, I managed to convince my prosthetist to
order such a knee and… what happened then is a disgrace.
The knee was defective, we couldn’t get tech-support in
English, they did not answer any request and eventually
blamed the prosthetist for the faulty knee demanding
$2,000 for repair.
Made me proud to be French!
1P50R Hydracadence II

The 1P50R Hydracadence II is a single axis hydraulic knee.
The coupling between knee angle and foot angle is
hydraulic. In addition, to its unique ability to improve toe
clearance, the system provides a smoother and safer
transition to load bearing at heel strike. It is a very clever
system and it’s a shame that their service and support is so
poor in the US.
I propose to build a similar system using a simpler
mechanical coupling between knee and foot with the
following requirements:
Toe rise for 0 < α < α 1 (terminal phase of swing)
and
rigid foot/knee coupling (90°) for α = 0 and α > α1
1P50R Hydracadence II

The kinematics of a hip-joint/knee/foot with such requirements
is beyond the paper and pencil approach.
Three possibilities
1) LEGO
YES! I hear you laughing but you would be surprised to see what can be done with the LEGO technics pieces. I even
built a functioning clock escapement to impress the kids. (Photos lost unfortunately)
2) COMPUTER MODELING
There are many software solutions. However, most are designed for the professional community and very
expensive. In addition, the learning curve with such programs is extremely steep. GOOGLE created SKETCHUP, a
FREE 3D modeling package. It is powerful yet, relatively easy to learn. SKETCHYPHYSICS is a free plugin for
SKETCHUP based on the NEWTON SDK physics engine from NEWTON GAME DYNAMICS. SKETCHYPHYSICS is VERY
buggy but… it is FREE.
3) DO THE MATHS
Solve analytically the motion of each part of the system (Major Trigonometric Cluster F*@!&). Then, simulate in EXCEL.

HD – TOE CLEARANCE – KINEMATICS MODELING
First test of kinematics modeling with Google Sketchup and Sketchyphysics. Sketchup was primarily designed for
architects but can be used for other applications. 3D modelling is never easy but Google developed a user friendly
interface. Sketchyphysics on the other hand is obscure and buggy but is the only free application I could find.

Four-Bar Linkage Animation using Google Sketchup and Sketchyphysics Plug-In

HD – TOE CLEARANCE – KINEMATICS MODELING

Model or a 5-bar linkage
modelled in Sketchup8 and
Rendered in KERKYTHEA
KERKYTHEA is extremely
powerful. It is free and…
TOTALLY user UNFRIENDLY…

HD – KINEMATICS
TEH-LIN, a Taiwanese manufacturer, recently introduced
two 5-bar knees. These knees do not use a proper 5-bar
linkage but offer the possibility of altering the 4-bar
geometry and the centroid trajectory through the motion
of the knee.
It is difficult to measure accurately the geometry of the 4-
bar linkage and their documentation is rather vague on the
effect of the 5-th bar adjustment on knee stability and toe
clearance.
I proposed the following methodology to measure the
centroid trajectory for each knee.

HD – KINEMATICS MEASUREMENTS
1. Build a test jig consisting of a sheet of ½” plywood on a
stand and a pyramid adapter to support the knee
under test and a 30”x20” foam board
2. Build a test foot made of a ½”x1 ½” piece of wood with
three 12mm holes at the normal toe and heel location
and a pyramid adapter
3. Connect the test foot to the knee to be tested and
connect the knee to the test jig
4. Install 3 sharpies into each hole and bend the knee up
to 90° of flexion.
5. Each sharpie will provide a record of the toe, leg, heel
trajectory.
6. Adjust the 5th bar and repeat the measurement on a
new sheet of foam board.
Adapter
KNEE
Test Foot
Test Jig
Foam Board

HD – KINEMATICS PROCESSING
1. Photograph each foam board (SONY DSLR on a tripod)
using a longer focal length (70mm) to minimize
geometric distortions.
2. Process the photos in Photoshop. (Straighten, crop,
normalize)
3. Digitize the curves using ENGAUGE, a freeware curve
digitizing programs (quite good too!)
4. Compute the data in Excel and calculate the centroid
trajectory and toe clearance for each 5th bar
adjustment.
PROJECT IN PROGRESS
The test jig and test foot have been built but no
measurement and processing have been done yet.

TEH-LIN KK950 “FIVE”-BAR POLYCENTRIC KNEE

KNEE KINEMATIC ANALYSIS
The picture of the 4-bar polycentric prosthetic knee is
calibrated in dimensions using Photoshop. The axis
centered on the shank pylon is plotted, as well as the
projection of the top pyramid adapter. (Scale 1:1)
The coordinates of the joints of the 4-bar linkage are
measured relative to A, defined as the knee axis of
rotation. The angle of rotation of the knee is defined as
the angle of the pylon from vertical . (Scale 1:1)
x y D
A 0 0 104.5
B 103.3 15.9 60.1
C 58.3 -24 45.8
D 12.6 -21.4 24.8
NOTE: The
distance DC
is adjustable
4-Bar linkage
Geometry

-60
40
140
-100 0 100 200 300 400 500 600
KINEMATIC ANALYSIS
KINEMATIC MODELING – Base of Foot (Nominal Leg Length)
540mm
200mm
Shank Pylon
Microsoft Excel

KINEMATIC ANALYSIS
-60
40
140
-100 0 100 200 300 400 500 600
540mm
200mm
KINEMATIC MODELING – TOES
Shank Pylon
Microsoft Excel

KINEMATIC ANALYSIS
Some quick comments:
This is entirely done in EXCEL using video screen capture with VLC media player.
And YES! I did suffer and banged my head on the wall on a few occasions. However, I took the opportunity to
dramatically enrich my vocabulary in trigonometric obscenities… And do not let me into the cluster f#@*#! of video
codecs compatibles with just about nothing else….
1) Between 0° and 40°, the toes do not clear the floor.
2) The gain in toe clearance provided by the polycentric design is very small.
3) The centroid of rotation between 0 and 13 degrees of flexion is BELOW the reference axis!!! However, over the
same range, the centroid remains posterior to the reference axis providing added stability.
Note: The motion of each leg component is calculated from classic trigonometry. The centroid is calculated as the
center of a circle passing through three adjacent points of the trajectory.

KINEMATIC ANALYSIS
-40
-20
0
20
40
0 5 10 15 20 25 30 35 40 45 50
Toe elevation
Toe Circle
Floor
Flexion (°)
Leg Vertical Length Variation as a Function of Knee Flexion
Between 0 and 40°, the apparent vertical
length of the leg exceeds the nominal
length (i.e. The toes do not clear the
floor).
The blue curve represent the toes
elevation relative to floor for the
polycentric knee.
The orange curve represent the toes
elevation relative to floor for a single axis
knee.
The gain in toe-clearance from the
polycentric knee is marginal.
ToeElevationRelativetoFloor(mm)

KINEMATIC ANALYSIS
0
1
2
3
4
5
0 5 10 15 20 25 30 35 40 45 50
Difference Polycentric-Single Axis
Floor
Flexion (°)DifferencePolycentrictoSingleAxis(mm)
The gain in toe clearance from the
Polycentric Knee between 0° and 40°
is less than 4mm.
The maximum is 3.8mm at 33° of
flexion.
The green curve represents the
difference in toe elevation relative to
floor between the polycentric knee
and a single axis knee.
NEXT STEP? VALIDATE THESE RESULTS
USING THE TEST JIG. NOT DONE YET.

HD - COMPONENTS
• The only way to evaluate and compare the capabilities of commercial prosthetic
components is to test them.
• However, as I explain earlier the cost of these components is astronomical. So, what do
we do?
• Thanks to EBAY, used components are affordable. The current market value of used or
even brand new prosthetic components is around 1 to 2 percent of the retail price.
• YES, YOU READ WELL. 1% TO 2% OF THE RETAIL PRICE!!
• Some examples below….
• TEH-LIN TGK5P00 KNEE MSRP $12,500 EBAY $175 1.4%
• TEH-LIN KK150 KNEE (BRAND NEW) MRSP $15,100 EBAY $160 1.1%
• MOBI OP4 KNEE (BRAND NEW) MSRP $11,000 EBAY $180 1.6%

HD - COMPONENTS
• The prices on EBAY are low today because the demand is low. WHY?
• Prosthetist do not and cannot use used components.
Apparently for insurance reason. Sounds like a good excuse to me, as they
make significant profit on the components.
• The prosthetic market is quite unique as the customer (the amputee)
doesn’t decide what components to use.

HD - COMPONENTS
• The customer has a good medical insurance. The prosthetist will order the
most expensive (not necessarily the most appropriate) components the insurance
accept to pay. If the leg doesn’t work, it will eventually end up on EBAY.
• The customer does not have medical insurance. The prosthetist will order
the cheapest components. Nevertheless, the leg will still cost $20,000 (AK).
The leg doesn’t work and the amputee will sell the components on EBAY.
• The customer does not have medical insurance and doesn’t have $20,000.
NO PROBLEMS! He can buy a pair of crutches at Walgreen for $20! Or,
beg at the traffic light. In less than 15 years, he will have enough money for
a leg… Unless he jumped under the 18-wheeler, of course….

HD - COMPONENTS
• Most customer have complete faith in their prosthetist. Coping
with the grief associated to recent limb loss and with no knowledge of prosthetic
technology and practices, the new amputee relies completely on the person with
the white lab coat talking with complicated words to put them back on two legs
again.
• The very large majority of prosthetists are honest and do the best they can for
their patients. However, they are human, often overworked and with their own
constraints.
• To become a Board Certified O&P practitioner is a 2-year degree, not 7 like an M.D.
Some are good and some are… “less good”.

HD - COMPONENTS
• We have a large community of amputees in
the US (1.7 millions).
• 91% are lower limb amputees, most
resulting from vascular disease (66%) and
(20%) from trauma. Lower limb amputees
from vascular diseases often suffer from
additional conditions and may not be able
to use their prosthetic leg. In addition, they
have a high mortality rate. The leg
components are sold on EBAY.
Cause of Amputation in the US

HD - COMPONENTS
• Most amputees rely completely on their prosthetists.
• Prosthetists cannot use “used” components.
• There are over 1.5 millions lower extremity amputees in the US.
• Therefore, we have a market with a large supply and low demand.
As a result…….

PROSTHETICS
MY COLLECTION
ORTHO EUROPE ULTIMATE KNEE: Single
Axis – Adjustable hydraulic damping for
flexion and extension – Adjustable
weight activated stance control

PROSTHETICS
MOBI-OP4: Single Axis –
Adjustable pneumatic damping
for flexion and extension –
Weight activated stance control
ENDOLITE: Single Axis –
Adjustable hydraulic
damping for flexion and
extension – Weight
activated stance control
GRAPHLITE TCG-PS0: Polycentric 5-bar with
adjustable centroid– Carbon fiber frame -
Adjustable pneumatic damping for flexion and
extension –stance flexion control
ORTHO EUROPE: Single
Axis – Adjustable
hydraulic damping for
flexion and extension –
Weight activated stance
control
GRAPHLITE
frame/ENDOLITE
cylinder: Single Axis –
Adjustable hydraulic
damping for flexion and
extension
OTTO-BOCK 3R60:
Polycentric–
Adjustable
hydraulic damping
for flexion and
extension – EBC for
stance flexion
ORTHO EUROPE: 2
Partial collection of
prosthetic knees

PROSTHETICS
Partial collection
of prosthetic feet

PROSTHETICS
Partial collection of
30mm prosthetic
pylons (aluminum
and carbon fiber) Carbon Fiber
Carbon Fiber
Carbon Fiber
Carbon Fiber
Pylons with integral
Pyramid Adapter

Partial collection of various
pyramid adapter/tube
clamps. Mainly polished
Titanium, some Stainless
Steel and Aluminum.
Adjustable Offset
Adapter (Titanium)
Adjustable Height
Adapter (Titanium)
(Aluminum)
Angled Adapter
for HD Prosthesis
(Titanium)
Male Adapter
(Titanium)

PROSTHESIS FOR HIP DISARTICULATION AMPUTEES - STUDY

PROSTHESIS FOR HIP DISARTICULATION AMPUTEES - STUDY

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