KNEE DISARTICULATION

PROSTHETICS

MI/Prosthetics manual/BPO/LLP/Aug 2009

 Chapter 1
Knee Disarticulation

1.1 Introduction
The knee disarticulation level of amputation
is also called the through-knee amputation.
The amputation is carried out on the joint
line itself.
The condyles of the femur are then used as
the weight bearing surface.

Many different approaches have been taken Fig 1.1 End bearing
in fitting the knee disarticulation prosthesis.
They usually use the end-bearing nature of The supracondylar area of the femur is still
the stump. intact and is bulbous in shape, and is able to
The method of suspension usually uses the be used for suspension. The socket is self-
supracondylar area. The knee mechanisms suspending and no other straps are required.
always try to reduce the length of the thigh
in their positioning set-up. The major muscle groups are intact and can
be fastened to the end of the femur. This
Energy consumption during gait for the knee makes the stump very powerful and the
disarticulation amputee will be higher than patient can control the prosthesis very well.
the transtibial amputee but lower than The long lever arm helps to reduce socket
transfemoral amputee. forces on the stump and increases the
comfort and control.

The Triangular shape of the epicondyles and

1.2 Advantages patella can be used to restrict rotation
between socket and stump. The shape of the
The major advantage of the knee supracondylar area can also control rotation,
disarticulation level of amputation, as especially when used for suspension.
opposed to the transfemoral level, is that it is
end-bearing. This means that the amputee is In children the knee disarticulation
able to put all his weight onto the end of the amputation has additional advantages. The
stump. stump will not grow as quickly as the sound
side. As the child grows the stump will
appear to shorten, when compared to the
sound limb. This will allow the use of
normal prosthetic knee joints later in life.
Also, the chance of bony overgrowth is
reduced because bone is not cut, so the
muscles and bone grow at the same rate.

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1.3 Disadvantages
The major disadvantage is that the long
stump makes it difficult for the prosthetist to
fit a knee joint at the distal end of the stump
without making the thigh too long and shank
too short. The knee centre will be too low
(Fig. 1.2).. This will affect the biomechanics
of walking, with the shank swinging more
quickly, and produce uneven timing.
Another concern will be the cosmesis, as the
thigh section will be noticeably longer,
especially when seated.

The alternative is to fit knee joints on the

outside of the socket at the correct height.
The problem with this method is that the
joints make the M-L diameter of the knee
much bigger than the natural leg.
Fig 1.2 Knee centre
The bulbous end of the stump usually makes
it very easy to achieve good suspension. The One disadvantage of the knee disarticulation
problem is in donning and doffing the stump, is that over the long term the distal
prosthesis. There are different ways of tissues atrophy. (The muscles that were used
dealing with this and are discussed in the to control the knee no longer function to full
Chapter 8, Socket variations. capacity). This leaves the posterior aspect of
the femoral condyles quite prominent. This
area can develop problems with pressure and
sheer forces (especially for donning and
doffing the prosthesis).
Some surgeons perform a reduction
osteoplasty to reduce this problem. (See
Chapter 2)

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 Chapter 2
Amputation Surgery

2.1 Objectives
The surgeon must aim to make a stump that is well covered with high quality skin and is
comfortable in end bearing.

The major blood vessels are tied off and cut. The nerves are pulled down, tied and then
cut, allowing them to pull back up into the stump.

The major muscle groups must be attached to the femur in a way that will allow them to
function well.

It is important that the soft tissue on the end of the stump is not stuck to the bone. The
effects of shear forces in the socket can damage adherent scars.

2.2 Limitations
The knee disarticulation must only be carried out if the knee is beyond saving. A short
below-knee stump will usually perform better. The amputation through the knee will be
carried out under the following conditions:
o If the potential transtibial stump is shorter than tibial tubercle level.
o If the knee is dysfunctional, that is if it has damaged ligaments or if it has a severe
flexion contraction.
o If there is not enough skin to cover the end of a transtibial stump.

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 Fig 2.1 Sagittal flap – Anterior view

2.3 Surgical Procedure

Sagittal Flaps
The skin is cut as shown in (Fig.2.1).

The patella tendon is cut from the tibial tubercle. The knee capsule is cut
circumferentially at the level of the joint and the cruciate ligaments are cut from the tibia.
The patella tendon is sutured to the remnants of the cruciate ligaments. The same is done
for the hamstrings. The gastrocnemius is used as an end pad and is sutured to the remains
of the joint capsule. The skin flaps are trimmed and sutured together to cover the stump.

Anterior Posterior Skin Flaps

The skin is cut as shown in Fig. 2.2.

In this method the hamstrings and the patella tendon are pulled under the femur and
sutured to one another under optimal tension. The skin cover is achieved by cutting a
long anterior flap and a short posterior one.

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 Figure 2.2 Anterior Posterior skin flap – Lateral view

Circumferential Incision
The skin is cut as shown in Fig.2.3.

In this amputation no flaps are produced. This is a good technique when good skin is hard
to find.
The surgery must be done with the patient in the prone position. The knee is flexed 90
degrees and the skin is cut circumferentially 1.5 cm below the tibial tubercle. The
ligaments and joint capsule are cut circumferentially at the joint level. The patella tendon
and hamstrings are sutured to the remnants of the cruciates to give firm anchorage. The
skin is trimmed and closed in a line medial to lateral.

Fig. 2.3 Circumferential incision

2.4 Treatment of Muscles and Ligaments

Figures 2.4 and 2.5 show the cutting and suturing of ligaments to stabilize the muscles.

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 Fig. 2.4 shows the ligaments and knee joint capsule being cut

Fig 2.5 shows the patella tendon and hamstrings sutured to the cruciate ligaments.

2.5 Reduction Osteoplasty

In order to get a better cosmetic effect some surgeons suggest that the amputation should
be carried out a little higher up to improve cosmesis (Fig 2.6). This will give the stump a
flat end and not a peaked end as is natural. It is also possible to trim the condyles. This
will reduce the size of the distal end. It will also increase the pressure because of the
smaller area and will also reduce the suspension.

Fig 2.6 Reducti

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 Chapter 3
Biomechanics

3.1 Socket

ML forces during stance

phase

The Transfemoral prosthesis bears the

patient's load on the Ischial seat (Fig 3.1).
The centre of rotation is the Ischial seat Fig 3.2 Knee disarticulation biomechanics
where it contacts the ischial tuberosity. The
end of the femur is relatively free to shift proximal end of the socket is therefore able
laterally within the soft tissue. The socket is to shift laterally as the soft tissue is
flattened laterally to reduce that movement. compressed. In effect the knee
disarticulation socket biomechanics are the
reverse of the Transfemoral.

The proximal brim of the knee

disarticulation socket is shaped to reduce the
range of movement of the socket on the
proximal stump. There must be good
support of the proximal-medial tissue of the
stump. The proximal brim usually has no
need of an ischial seat because it usually has
no need to carry load. However the
quadrilateral brim will give good proximal
control.
Fig. 3.1 Transfemoral biomechanics The posterior wall does not make contact
with the ischium and is much narrower than
With a good knee disarticulation stump all the transfemoral seat. Since the anterior wall
the load is taken on the distal end (Fig 3.2). is not required to provide the counter force
In the knee disarticulation socket the distal to the ischial seat it can be trimmed much
end of the stump is held securely (as it is lower. Seated comfort is much improved.
weight bearing) and is unable to move. The The anatomical shape of the quadrilateral
centre of rotation is the distal end of the brim helps to control the M-L and A-P
stump. The non-load bearing shifting of the socket on the proximal stump.
It also helps to prevent rotation of the socket

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on the stump.

During stance phase in the transfemoral

prosthesis the body’s centre of gravity acts
at a distance from the point of support at the
end of the stump (Fig 3.3). This causes a
tendency for the body to rotate towards the
unsupported side. The rotation is controlled
by the action of the hip abductor muscles.
This causes a tendency for the femur to
move laterally in the transfemoral socket
and most of the pressure will be distal-
lateral in the socket.

Fig 3.4 Stance phase - anterior view

Fig 3.3 Stance phase - posterior view

In the knee disarticulation socket however,

the end of the stump is usually fully weight
bearing and thus very stable (Fig. 3.4). As a
result, the socket tends to shift laterally at
the proximal end of the stump. Most of the
pressure will be proximal-medial in the
socket.

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3.2 AP forces during
stance phase
When viewed from the lateral side the forces
in the knee disarticulation socket at heel
strike (Fig.3.5) are similar to those in the
transfemoral. The patient actively extends
the hip and creates a posterior force distally
that extends the knee against the knee
extension stop.

Most knee disarticulation amputees do not

need involuntary stability in the form of
excessive anterior placement of the TKA
(Trochanter/Knee/Ankle) line, a manual
knee lock, or stance phase control knee. The
long lever arm and strong hip extensors can Figure 3.6 Mid-stance
create a powerful knee extension moment.
Therefore, voluntary control of knee Figure 3.7 shows push off as the amputee
stability is usually sufficient. Socket forces initiates swing phase with the hip flexors.
are located posterior-distal and anterior- Socket forces are located anterior-distal and
proximal. posterior-proximal.

Figure 3.5 Heel strike

Fig 3.7 Push off (end of stance phase)

At mid-stance (Fig. 3.6) the forces are
purely axial when viewed from the lateral
side. A TKA line that is about 5mm anterior
to the knee joint is usually sufficient to make
the knee stable.

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3.3 Swing phase discussed in Chapter 8, Socket variations.

During swing phase the weight of the

prosthesis is hanging on the stump. The 3.4 Rotational control
bulbous shape of the condyles of the femur
provides the ideal area to lock the socket A close fit around the triangular shape of the
onto the stump. Mild indents are made in the epicondyles and the patella (Fig. 3.9) are
supracondylar area (Fig. 3.8). used to restrict rotation between the socket
and the stump.

Fig 3.8 Suspension forces Fig. 3.9 Shape of epicondyles and patella

Supracondylar suspension should not be The shape of the supracondylar suspension

used if the patient cannot bear weight on the area (Fig. 3.10) can also control rotation.
end of the stump. This type of patient will
need an ischial weight bearing socket.
The problem of providing an ischial weight
bearing socket and supracondylar
suspension is that at certain times the
ischium will push the prosthesis down onto
the supracondylar area and cause
discomfort/pain. Fig. 3.10 Transectional view of socket at
The times that this will happen are: supracondylar level
From mid-stance to toe-off, as the
ischium is strongly in contact with In addition, the proximal medial wall of the
the seat, and the distance from the socket can be flattened to help give some
ischium to the end of the stump rotational control. When there is a lot of soft
decreases. tissue around the stump a quadrilateral brim
Early swing phase, reducing as the can give improved rotational control.
leg swings through and distance Sometimes a silesian belt must be used for
between ischium and end of the maximum control.
stump increases

To allow the patient to get the leg on and off

over the bulbous end a variety of socket
designs are used. These will be further

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3.5 Summary
Biomechanically the knee disarticulation has
some big advantages, these are:

o The long stump has a larger area to

distribute pressures.
o A long lever arm and therefore small
M-L and A-P stabilizing forces
o Strong muscles giving improved
control of the prosthesis
o The bulbous end of the stump gives
very good suspension
o The stump can usually tolerate end
bearing

The main disadvantages are:

o The difficulty in fitting a prosthetic

knee under the stump without
making the thigh too long and the
shank too short
o Poor cosmesis
o Donning and doffing over the
bulbous distal end.

See also, page 42 Four Bar Linkage.

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 Chapter 4
Anatomy
4.1 The Femur
The Femur transmits the weight from the The layer of soft tissue covering the distal
ilium to the upper end of tibia. end is usually quite thin and therefore it
should be easy to feel and see the structure
The normal amputation procedure will leave of the end of the stump. The most important
the distal end of femur unchanged. bony structures are shown below.

Fig 4.1 Right femur

It is important to understand the anatomy of intercondyloid fossa, because stretching of

the distal end of the stump. The main load the skin into this area maybe painful.
bearing areas are the femoral condyles. Very
little pressure should be applied to the

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 is triangular in shape, with its apex
The Patella positioning downwards and its base
uppermost. (Human Anatomy, p.315)
The patella is a sesamoid bone formed in the
tendon of the quadriceps femoris muscle. It

Fig.4.3 Right femur viewed from below.

The patella is not always present in the

stump. When present, its position and
condition can vary greatly. The patella
should be fastened to the cruciate ligaments
and pulled towards the end of the stump to a
position where it can be loaded. But in some
cases it sits quite proximal on the stump. It
may be mobile or fixed.

Fig.4.4 The patella

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4.2 Surface Landmarks
On the surface of the stump the structures shown below are most important landmarks that need
to be recognized.

Fig. 4.5 Right stump - posterior view Fig.4.6 Right stump - anterior vie

4.3 Muscles around the It must be remembered that during many of

these movements the hip joint is weight
hip joint bearing, transmitting weight of the body
above it, via the lower limbs, to the ground.
The hip joint is a ball and socket joint Thus, the muscles surrounding the joint have
capable of movement in many directions. To a dual role. They must be capable of
produce these movements there is complex immediate controlled power when needed
arrangements of muscles around the joint. for sudden powerful activities and but also
be able to maintain a set position for long
periods of time.

Table 4.1 Muscles acting on the hip joint. (Fill this in for yourself, it will be a useful revision)

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1 MUSCLES EXTENDING THE HIP JOINT
MUSCLE ORIGIN INSERTION NERVE SUPPLY
Gluteus Maximus
The Hamstrings
o Semitendinosus
o Semimembranosus
o Biceps Femoris

2 MUSCLES ABDUCTING THE HIP JOINT

MUSCLE ORIGIN INSERTION NERVE SUPPLY
Gluteus Maximus
Gluteus Medius
Gluteus Minimus
Tensor Fascia Latae

3 MUSCLES ADDUCTING THE HIP JOINT

MUSCLE ORIGIN INSERTION NERVE SUPPLY
Adductor Magnus
Adductor Longus
Adductor Brevis
Gracilis
Pectineus

4 MUSCLES FLEXING THE HIP JOINT

MUSCLE ORIGIN INSERTION NERVE SUPPLY
Psoas Major
Iliacus
Rectus Femoris
Sartorius
Pectineus

In addition to the extension, abduction, adduction and flexion movements,

medial and lateral rotations of hip are produced by the combination of many muscles, or
parts of them.

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 Chapter 5
Patient Assessment
like to do better.
5.1 Introduction o Find out how important cosmesis is
to the patient.
This information will help you to choose the
The similarities between the transfemoral
best prescription.
stump and the knee disarticulation stump are
very great. The procedure for assessing the
function of the hip joint in terms of muscle 5.2 The Distal End
strength and range of motion can be taken
directly from the Transfemoral Prosthetics 1. Examine the skin. Is it healthy and
manual. It is expected that the muscle strong?
strength will be greater in this amputation
level because the muscles will be normal in 2. Examine the scar. Is the scar strong,
length and well anchored. non-adherent, and in a position
where it will not be damaged?
The Transtibial Prosthetics manual can be
referred to for assessment of the skin 3. Palpate the intercondyloid fossa. Can
condition. The major difference occurs at the skin be stretched into the groove?
the end of the stump in the end bearing Is it painful? This will tell if the
characteristics. socket can be molded into the groove
or not.
Make a thorough assessment of the general
condition of the sound side. Carefully assess 4. Push hard on the distal end and see if
muscle strength and range of motion at the the patient has pain. Ask the patient
hip, knee, and ankle. Problems on the sound to place their weight onto the distal
side can greatly affect the fitting of the end of the stump. Check all the bony
prosthesis. prominences including the edges of
Also do a quick check of upper limb and the medial and lateral epicondyles
hand function. and the adductor tubercle. Can the
distal end bear weight or will ischial
In addition, carefully involve the patient in weight bearing be needed?
the assessment procedure.
o You can get the best result if you let
the patient be a part of making
decisions about the prescription.
Talk in detail with the patient about
the activities at home and at work.
o Find out what activities the patient
needs to do every day.
o Find out what activities the patient Figure 5.1 Checking the bony edges of the
would like to be able to do or would lateral epicondyles.

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 5.3 Checking the patella

6. Assess the supracondylar areas. Are

they able to tolerate pressure for
supracondylar suspension? Note the
prominence of the bony structures.

7. Measure the circumference and

diameter of the bulbous end.
Measure the circumference and
diameter of the thigh at 5 cm
intervals up from the bulbous end. At
what level on the thigh are the
measurements the same as the
bulbous end? This will help to
determine the type of socket design
Figure 5.2 Checking the bony edges of the
needed for the bulbous end to easily
medial epicondyle and adductor tubercle.
enter the socket.
5. Check for the presence of a patella.
Is it mobile or not? Is movement
pain free? Assess and note the
amount of movement that needs to
be allowed in the socket to make the
patella comfortable.

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MI/Prosthetics manual/BPO/LLP/Aug 2009
 Chapter 6
Casting Procedure
6.1 Introduction 6.3 The Aims
The aim of taking the plaster cast is to The aims for end bearing stump.
produce a socket that reflects the shape and
biomechanical features of the stump. The When the patient can bear weight on the end
cast should be shaped as much as possible of the stump the distal part of the cast should
during the casting procedure to emphasize be taken in weight bearing.
the natural attributes of the stump, especially
those parts of the stump that can be used for The proximal cast can be quadrilateral in
direct load bearing and suspension. shape. It does not need to be heavily defined
and should not touch the ischial tuberosity.
6.2 Stump Features The posterior wall should be about 1.5 cm
from the ischial tuberosity.
o The knee disarticulation stump
usually has the ability to bear the If the distal end of the stump is fully weight
patient's total weight on the end of bearing, the proximal brim does not need to
the stump. be quadrilateral in shape.
o The end of the stump is usually It can be oval shape, slightly flattened on
bulbous, so it is not always easy to medial and lateral aspects.
remove the cast from the stump. A
plastic tube or strip should be placed The height of the medial wall can be up to 5
on the stump before casting so that cm below the perineum with the lateral wall
the cast can be safely cut for sloping up to the greater trochanter. The
removal. medial wall can be flattened to give
o The bulbous shape of the femoral rotational control. The edges of the socket
condyles can be used for suspension. should be flared.
o The proximal stump will require
protection from excessive pressure Whether the proximal brim is quadrilateral
from the upper edge of the socket. A or not, it should be as high as possible. This
quadrilateral brim can provide this will make a long lever arm and reduce
protection. The edges of the brim socket forces during gait.
that is lower than in quadrilateral TF
socket must be flared.

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The aims for non-end bearing
stump.

The distal stump should not be cast during

weight bearing if the patient can not bear
weight on the end of the stump. The socket
must be ischial weight bearing and the
proximal brim of the cast should be molded
as for a transfemoral patient.

Supracondylar suspension cannot be used

when the proximal brim is ischial weight
bearing. If supracondylar suspension is used,
the weight bearing pressure on the ischial
tuberosity will push the socket off the stump
slightly. Fig. 6.1 The casting stand
Most pressure will come onto the seat at
mid-late stance phase and early swing phase, 5. A stool or casting stand (Fig 6.1)
as the hip is in extension and the distance with 20mm of foam padding set up
from the ischium to the supracondylar area so the patient can weight bear on the
is at a minimum. At this point there will be a end of the stump at the correct
force pulling the limb out of the socket. This height.
will cause pain on the femoral epicondyles. 6. Four rolls of 15cm plaster bandage.
Alternative transfemoral suspension 7. Cast saw or sharp knife.
methods can be used for an ischial weight 8. An assistant will also be required.
bearing socket. Special attention should be
made to ensure adequate relief for the 6.5 Procedure
condyles in an ischial weight bearing socket.
1. Make a full assessment of the patient
and note the findings on the chart.
6.4 Equipment required
2. Take all measurements as shown on
1. Cast sock long enough to cover the the chart.
whole stump. This should be a tight
fit, but not too tight to cause 3. Set up the casting stand at the height
wrinkles. required for the patient to stand with
2. Elastic straps to hold up the cast the pelvis level if the cast will be
sock. taken during weight bearing.
3. Indelible pencil.
4. Plastic tube or strip to protect the 4. Prepare a plaster slab for the
stump from the knife. proximal end of the stump if the
brim will have a quadrilateral shape.
It should be long enough to go
around the top of the stump and
should have a cut-out for the
adductor longus tendon.

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 5. Put the cast sock (slightly wet) on
the stump and hold it in place with
the elastic strap.

Fig. 6.3 Anterior landmarks on the cast sock

Fig. 6.2 Cast sock with anterior tube

6. Place the plastic tube down the

anterior mid-line inside the sock (Fig
6.2)
7. With the patient standing, mark the
following landmarks with indelible Fig 6.4 Posterior landmarks on the cast sock
pencil.
o Greater trochanter 8. Wet the plaster bandage, and with
o Adductor longus tendon the patient non-weight bearing, wrap
o Patella (if it is present) the distal third of the stump. Make
o Femoral condyles and epicondyles sure the plaster is 3 to 4 layers thick.
o Hamstring tendons When the plaster has been applied,
o Intercondylar fossa (on distal end) mold it closely to the stump and then
o Any scars or bony prominences ask the patient to bear weight on the
casting stand if the stump is end
bearing (Fig 6.5). Remember to
check the alignment of your stump
at this time.

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 in the line of progression to give
rotational control.

12. The assistant can then shape and

mold the supracondylar area of the
stump if the socket will be end
bearing and not ischial bearing (Fig
6.7).

Fig 6.5 Wrapping the distal end.

9. Continue to wrap the stump in

plaster up to the proximal end.

10. Apply the proximal slab if a

quadrilateral brim will be used.
Stand on the patient's lateral side and
apply the wet slab. Position the cut-
out part on the adductor longus
tendon and pull the two ends of the
slab around the stump in opposite
directions. They should overlap on
the greater trochanter. Using the Fig 6.7 Moulding the supracondylar suspension
hands as shown in the Transfemoral
Prosthetics manual in the chapter on
hand casting, shape the proximal
cast to a quadrilateral shape (Fig
6.6).

Fig 6.6 Shaping the quadrilateral brim

11. When a quadrilateral brim will not

be used, wrap up to the groin area
and to the greater trochanter on the
lateral side. Flatten the medial wall

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 13. When the plaster is set, plumb lines 16. When filling the cast, it is advisable
are drawn on the anterior and lateral to fill it with the tube or mandrill
sides while the patient stands parallel to the plumb lines.
comfortably weight bearing. These
lines will show the flexion and 17. Always be helpful and respectful to
adduction angles for bench the patient. Assist with cleaning and
alignment. A line can also be drawn dressing.
on the bottom of the cast showing
the line of progression. This line can
help when determining knee joint
rotation during bench alignment.

14. The cast is removed by first marking

the position of the plastic tube, cross
marking and then cutting along it
carefully. Great care is taken not to
distort the cast. The cast must be
returned to its normal shape and
sealed.

Fig 6.8 Removing the cast

15. If the brim is quadrilateral, the

negative cast is rectified before
filling as described in the
Transfemoral Prosthetics manual in
the section on hand casting.

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MI/Prosthetics manual/BPO/LLP/Aug 2009
 Chapter 7
Cast Rectification
The usual cast rectification procedures are
7.1 Preparing for carried out:

Rectification 1. The plumb lines are transferred to the

cast.
The aim of the rectification procedure is to 2. The cast is cleaned and tidied and the
produce a cast over which a good socket can marks re-drawn.
be made. The socket should load the areas of 3. The cast measurements are checked
the stump which are tolerant to pressure, and and goals are decided on.
unload the areas which are sensitive to
pressure. 7.2 Establish the Goals
The main area of the stump which is
pressure tolerant is the femoral condyles at The proximal soft tissue area
the distal end of the femur. In most cases the
weight of the patient can be carried through For a socket that will not have a quadrilateral
the end of the stump. brim or for a socket that will have a
quadrilateral brim but not be ischial bearing,
In some cases, the end of the stump is the cast circumference is reduced to compress
pressure sensitive and unable to carry the the soft tissues to give a close fit. The
patient's weight. When this is found during proximal brim is shaped so that it will reduce
the patient assessment procedure, it is the tendency for rotation, give sitting comfort
important that the cast is rectified so that the and allow room for active muscles.
patient's weight is carried through the ischial
tuberosity as with transfemoral prosthesis. A general guideline is that the reduction
should be half of what it would be for a
The areas that are sensitive to pressure are: transfemoral cast.
o Patella
o Femoral epicondyles For a socket that will have a quadrilateral
o Adductor tubercle brim with ischial weight bearing, the
o Hamstring tendons rectification procedures described in the
o Any scarred areas Transfemoral Prosthetics manual are
followed.

Remember that a bigger /softer /fatter stump

is reduced more, and a smaller/ firmer/leaner
stump is reduced less.

The supracondylar diameter

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 Fig 7.1 The medial-proximal wall is reduced and
Suspension of the prosthesis for a socket shaped.
that is not ischial weight bearing is made by
reducing this area according to the diameter The lateral-proximal wall is reduced
measurements made of the stump. and shaped
For ischial weight bearing sockets, the 1. This area should be flattened for even
supracondylar area is not reduced. pressure distribution.
2. Care should be taken that the M-L
The distal bulbous end of stump diameter is correct.
3. For the socket without quadrilateral
The cast must be rectified so there is no brim, the height of the lateral wall can
pressure on the epicondyles. With bony be at the level of the greater trochanter
stumps the cast diameter will end up being or as high as possible for force
bigger than that of the patient. distribution.

7.3 Cast Reductions

The medial-proximal wall is
reduced and shaped

1. This area should be flattened to

follow the line of progression, and
avoid pressure at the top of the brim.
2. Attention should be paid to the
amount of rotation between the
medial proximal wall and the
triangular shape of the patella and Fig 7.2 The lateral-proximal wall is reduced and
epicondyles. shaped.
3. For the socket without quadrilateral The anterior-proximal wall is
brim, the height of the medial wall reduced and shaped
should be no more than 5 cm below
the level of the ischial tuberosity but 1. This area should be shaped like the
it should be kept as high as possible. scarpas area of the transfemoral cast
but the shape need not be as prominent
if the socket will not be ischial weight
bearing.
2. For the socket without quadrilateral
brim, the anterior proximal brim can
have a more rounded shape.

The posterior-proximal wall is

reduced and shaped
1. This area should be flattened to allow
for sitting comfort and to avoid

MI/Prosthetics manual/BPO/LLP/Aug 2009

 pressure at the top of the brim. No
Ischial bearing should be made
unless the stump is painful at end
bearing.

Fig 7.4 The supracondylar area is reduced and

shaped

Fig 7.3 The posterior-proximal wall is reduced

and shaped

The supracondylar area is reduced

1. For sockets without ischial weight

bearing, the supracondylar area of
the cast is reduced to provide
suspension of the socket. The M-L
diameter of the finished cast must
match the measurement taken of the
stump during casting.
2. Just above the epicondyles the
reduction is quite sharp, but it blends
gently and smoothly towards the
proximal part.
3. For ischial weight bearing sockets,
the supracondylar area is not
reduced.

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7.4 Cast Build-ups
Trim lines for sockets without
quadrilateral brim.

1. The trim should be as high as

possible to give a long lever arm,
which will reduce pressures at the
trim line.
2. Medially, it should not be more than
5 cm below the ischial
tuberosity/pubis ramus level.
3. Anteroriorly and laterally it should
Fig.7.6 Posterior trim lines
be a little higher than medial and
posterior walls.
4. A small flare should be made
The medial and lateral epicondyles
anteriorly, medially and posteriorly, are built up
but not at the lateral aspect of the
cast. 1. The bony prominences of the
epicondyles are built up to avoid
pressure.
2. If the stump is bony, the build-ups are
bigger than if the stump is well padded
with soft tissue.
3. The shape should be nearly square
both distally and proximally, with less
build-up at the apex.

Fig 7.5 Anterior trim lines.

Fig 7.7 The medial and lateral epicondyles are

buil-up

4. Special attention should be given to

avoid pressure on the adductor
tubercle.

MI/Prosthetics manual/BPO/LLP/Aug 2009

 5. When looking at the build-ups from
the lateral and medial they should
follow the proximal curve of the
epicondyles.

Fig 7.9 The posterior flare at the condyles is built

up

The patella area is built up (if

Fig 7.8 The curve of the epicondyles is followed present)

The posterior flare of the condyles 1. A few millimeters of plaster is built up

is built up on the patella if it has not been
removed.
1. The posterior area of the condyles is 2. If the patella is mobile, it is important
built up a little. to extend the build-up proximally and
2. If the hamstring tendons are distally to allow room for the
prominent a build-up should be made movement
to allow room for muscle action.
3. Also if there is a large indentation Finally, the cast is smoothed and
posteriorly the area should be built measurements are checked
up.
4. If the intercondylar notch has been
found to be pressure sensitive it is
also necessary to make a small build-
up here.

MI/Prosthetics manual/BPO/LLP/Aug 2009

 Chapter 8
Socket Variations and Materials
8.1 Introduction re-inserted. The shape of the panel allows it
to grip the supracondylar area.

The knee disarticulation socket has the same

functions as sockets for other levels of
amputation.

o It must transmit the load of the

patient to the structure of the limb in
a comfortable and biomechanically
acceptable way.
o It must distribute socket forces
comfortably during gait.
o It must be secure in its suspension.

The long end bearing stump usually makes it

very easy to transmit load and distribute
socket forces. The bulbous end of the stump
usually also makes it very easy to achieve
good suspension.
Fig.8.1 Removable panel
The problem is in putting on and off the leg.
The bulbous end must be accommodated
and yet the socket must be narrow proximal
to the condyles for good suspension. There
are different ways of dealing with this.

8.2 Suspension design

1 The Removable Panel

In this solution, the socket has a cut out

section in the side wall. This is removed,
allowing the patient to push the stump past
the narrow supracondylar area. When the
stump is in the correct position the panel is

MI/Prosthetics manual/BPO/LLP/Aug 2009

2 Push Fit Liner

In this case, the stump is first fitted with a

flexible liner. The inside of the liner is The patient first puts on the liner over his
shaped to fit the stump. The outside is built sock and then pushes the liner into the
up in the same material so that it is conical socket. The suspension between stump and
in shape. The conical shape may have a liner occurs above the condyles, and the
small narrowing at the supracondylar region suspension between liner and socket is a
of about 3mm in the M-L diameter. The result of friction. If the narrowing is correct
outer socket is made to fit over the liner. on the outside of the liner then the
suspension is even more secure.

Access to the liner can be made easier by

splitting it over part or all of it length. The
liner can be the full length of the stump or
just high enough to come proximal to the
supracondylar region.

Fig. 8.2 Supracondylar suspension

Fig.8.3 Push Fit Liner

3 Lacing

In this solution the socket is split from

proximal to distal on the anterior surface.
The split is joined by laces. The socket is
shaped for supracondylar suspension.

The patient puts on the leg by opening the

laces and then sliding the stump inside.

MI/Prosthetics manual/BPO/LLP/Aug 2009

When the stump is in the correct position the 8.3 Load Bearing Design
laces are tightened and tied.

This method relies on the use of a flexible 1 End Bearing Stump

material such as leather or soft
thermoplastic. The advantage is that the The end bearing stump can be treated with
patient with stump volume changes can or without a quadrilateral brim.
adjust the fit of the socket if the stump
swells or shrinks. The quadrilateral brim will help to evenly
distribute socket forces during gait because
of the high trim lines. It can also help to
control rotation of the socket on the stump.

The ischial seat of the quadrilateral brim

does not need to contact the ischial
tuberosity when the patient's stump end is
fully weight bearing

The ischial seat of the quadrilateral brim

should not contact the ischial tuberosity if
supracondylar suspension is used. Pressure
between the ischial seat and the ischial
tuberosity would tend to slightly push the
socket off the stump during late stance phase
and early swing phase. This would cause
pain on the medial and lateral epicondyles of
the femur.

2 Non-End bearing Stump

Fig.8.4 Leather lacing socket
The non-end bearing stump must be treated
4 Conventional Suspension with a quadrilateral brim. The ischial
tuberosity must bear weight on the ischial
If the patient is unable to tolerate seat of the socket to take all or some of the
supracondylar suspension then other weight off the distal end.
methods must be tried. The options are using
a silesian belt, a rigid pelvic band, or Supracondylar suspension should not be
neoprene etc. These are fully explained in used with the non-end bearing stump.
the Transfemoral Prosthetics manual. Pressure between the ischial seat and the
Suction sockets may be an option if a ischial tuberosity would tend to slightly push
flexible material can be used for the inner the socket off the stump during late stance
socket with a valve housed with rigid outer phase and early swing phase. This would
socket. If there is little or no flaring of the cause pain on the medial and lateral
distal femur, suction socket may also be epicondyles of the femur. The socket should
used. not be molded in the supracondylar area. A
Silesian belt or other type of suspension
must be used.

MI/Prosthetics manual/BPO/LLP/Aug 2009

8.4 Materials polypropylene may not provide adequate
strength. If such a socket is made, ensure
that the socket will not bow / twist during
The materials used are similar to those used
gait.
in other prosthetic devices. These include
thermoplastic, laminated GRP and leather.
Wood and metal have been used in the past 3 GRP
but the more modern materials have
generally taken their place. It is used in the same type of applications as
the polypropylene. It has been traditionally
1 Pelite - EVA-foam favored in panel type sockets. The majority
of four-bar knees are designed to be used
Generally used for the liner in the push fit with a GRP socket as the attachment point is
type of design. intended to be laminated into the socket.

2 Polypropylene 4 Leather

It is easy to mould and manufacture. It is In the lace type of socket, leather is a good
strong and durable. Polypropylene can be choice. It gets its strength from the use of
used in the panel, push fit or conventional side steels and external knee joints. It is not
socket. However, when using some types of strong enough on its own. Leather sockets
four-bar linkage knee joints, it is sometimes are functional and comfortable but have all
difficult to attach them to polypropylene. the problems already described in the
Considering the size of the panel and the Transfemoral Prosthetics manual.
forces in a knee disarticulation socket,

MI/Prosthetics manual/BPO/LLP/Aug 2009

 Chapter 9
Components

The following components of the prosthesis The exoskeletal shank will be used when
will be discussed here. Prosthesis is made with external knee joints
These are: and side steels. The material can vary
between aluminum, wood and plastics. The
1. The foot main concern when choosing the material
2. The shank for this type of shank is that it must be
3. The knee joint strong enough to carry the weight of the
4. The cosmesis patient through the relatively small area of
the side steels and often the proximal part of
9.1 The Foot the shin has to be reinforced for this
purpose.
The various types of feet are covered
The endoskeletal shank will be used with a
extensively in the Transtibial Prosthetics
four-bar linkage or single axis knee joint.
manual and are not discussed further here.
The set up will be modular. It is similar to
that of transfemoral prosthesis. (Refer to the
The use and prescription principles of feet
Transfemoral Prosthetics manual for further
for the knee disarticulation amputee are
details)
similar to those of the transfemoral amputee
and can be referred to in the Transfemoral
Prosthetics manual. 9.3 The Knee Joint
9.2 The Shank Section The big dilemma when making this type of
prosthesis is that of placing the knee joint in
a position which is anatomically correct.
The choice of shank falls between the two
The two basic problems are related to
basic types, the endoskeletal and the
cosmesis and the biomechanics of swing
exoskeletal design.
phase.

MI/Prosthetics manual/BPO/LLP/Aug 2009

1. Poor cosmesis When side bars are used, the M-L diameter
of the knee area becomes much bigger than
When the knee joint is placed under the end normal, because of the thickness of the
of the stump/socket, the thickness of the socket plus the thickness of the side bars.
socket materials, added to the space needed
to attach the joint and finally the knee joint
itself causes the joint to be more distal than
the anatomical joint.

This means that the thigh section of the

prosthesis becomes much longer than
normal and the shin becomes shorter. The
problem is especially noticeable when the
patient is sitting down, but some difference
can also be seen when the patient stands.

Fig.9.2 Large M-L diameter of external joints.

Fig.9.1 Poor cosmesis when sitting with joint
attached to distal end.
2. Biomechanics

When the joint is placed under the stump the

biomechanics of swing phase are affected.
The shank becomes much shorter than
normal and will act as a short pendulum.
The short pendulum will swing much faster
than a long pendulum and therefore the
speed of the swing phase will become faster
and the gait will be uneven.

MI/Prosthetics manual/BPO/LLP/Aug 2009

 joint to the proximal-anterior part of the
shin. The elastic will pull the shank section
into full extension at the end of swing phase.

Stance phase stability is achieved by

aligning the knee joint centre behind the
TKA line.

The advantage of this joint is that it is of

simple construction. As a result, it is easy
and cheap to make, and easy to repair and
maintain.

Fig.9.3 Pendulum action of shank.

9.4 Three Types of Knee

Joints
There are 3 basic types of knee joints for
this prosthesis, the single axis joint, external
joints with side bars, and the four-bar
linkage joint

1. The single axis knee joint

This is basically a modular knee joint where

the distance between the distal end of the Fig.9.4 Single axis joint with exoskeletal shank.
stump and the knee joint centre is kept as
small as possible. The disadvantages of the joint are that the
cosmesis is poor because of the long thigh
It is uncommon for single axis joints made section, and that there are few possibilities
for knee disarticulation prostheses to have for swing and stance phase control.
any form of internal (inside) swing and
stance phase control, as this would take up
too much space.

Most commonly the joint will be used with

an external extension aid in the form of an
elastic band. This elastic will run from the
anterior-distal socket in front of the knee

MI/Prosthetics manual/BPO/LLP/Aug 2009

 Fig.9.6 External joints with side steels.
Fig.9.5 Single axis knee joint with external aid.

2. External knee joints with side It is important that the joints are placed as
steels close to the socket as possible to maximize
These joints are similar to those used in the cosmesis.
orthotics and can be single axis or multiaxis.
They are attached to the outside of the This type of joint has a built in extension
socket. The joints are fixed to side steels, stop, but it is very close to the centre of
which are riveted to the socket and also to rotation and therefore the lever arm is very
the shank section. The shank is often made short. Also the surface area of the joint is
of metal or wood, but plastics can also be quite small. This means that the pressure on
used. the extension stop of the joint is very big so
it can break easily.
The knee axes are placed in an
approximation of the anatomical centre of It is often necessary, therefore, to add an
rotation. This is calculated by either of two extra (external/outside) extension stop on
methods. the posterior of the knee. It can be a nylon or
Marking a point 2cm proximal to the leather strap which runs from the distal part
end of the femur. of the socket to the proximal part of the
Taking a mid-point between the shank behind the knee joint. This 'ligament'
distal end of the femur and the helps the joint to stop extension of the knee
adductor tubercle. and is often called a back stop.
They are positioned just behind the TKA
line to give knee stability during stance Swing phase control can be in the form of an
phase. Posterior offset joints (joints that are external (outside) extension aid as described
made with the axis not in line with the for the single axis joint.
uprights) can be used to increase knee
stability. Stance phase stability can be achieved by
alignment but if the patient is very weak it is

MI/Prosthetics manual/BPO/LLP/Aug 2009

possible to add a knee lock. 3. Four-bar linkage joint
Usually this is a drop lock, which is dropped
over the joint and so locks it both in swing The four-bar knee is a system of hinges
and stance phase. For sitting the patient will connecting four bars. The four-bar knee
have to lift the drop lock with his hands so joint is polycentric. The joint is very stable
the joint can flex. in stance phase because the axis of rotation
lies posterior and proximal to the TKA line
when the knee is in full extension (Fig 19.7).

Fig.9.7 Drop lock.

The advantage, of external joints is that they Fig.9.8 Knee axis during full extension.
are positioned at the anatomically correct
height so the shank and thigh sections are The position of the centre of rotation
the correct length. changes as the knee flexes and extends. This
is similar to that of the anatomical knee
The disadvantages of external joints are that joint. Swing phase can look very close to
the M-L diameter is big which gives poor normal.
cosmesis. Also, alignment changes are
difficult to make as the side steels must be
removed and bent again. The extension stop
of the joint breaks easily and should be
assisted by a back stop. Lastly, there is no
extension bumper to prevent noise at the end
of swing phase.

MI/Prosthetics manual/BPO/LLP/Aug 2009

 Fig. 9.9 The axis of rotation changes when the
flexion angle changes

The joint is placed under the end of the

socket but because the axis of rotation
changes during flexion, the shank moves
posteriorly when flexing for sitting. This
improves cosmesis during sitting.

The four-bar knee joint also has a shortening

effect as the knee flexes. This improves toe
clearance during swing phase

MI/Prosthetics manual/BPO/LLP/Aug 2009

POLYCENTRIC KNEE - FOUR BAR LINKAGE

(Atlas of Amputations and Limb Deficiencies,2004, p.421)

Polycentric designs offer several biomechanical advantages and are

increasingly popular as a result.

A key distinction is that the functional center of rotation is generally

located outside of the knee joint itself. In a four-bar type of polycentric
knee, the instantaneous center of rotation (ICOR) can be determined
geometrically by drawing straight lines through the posterior and anterior
axes. The point where these lines intersect is the ICOR - the point in space
where his knee effectively articulates.

In a typical design, the ICOR is located posteriorly and proximally to the

mechanical knee axis.
The posterior position makes this knee inherently stable because the GRF is located far
anteriorly, thus generating a strong extension moment. As the amputee starts to flex the
knee, the ICOR changes; typically, it moves more anteriorly and distally with each
additional degree of knee flexion.
Once the knee has been flexed a few degrees, the ICOR falls in front of the GRF and a
flexion moment is created. This combination of a posterior ICOR at extension and a
much more anterior ICOR after a few degrees of knee flexion makes the typical
polycentric knee very stable in early stance phase and yet relatively easy to flex in late
stance, even under partial weight bearing.
The proximal location of the ICOR also gives the amputee a leverage advantage over an
articulation at the anatomic knee center, making it easier to voluntary control the
prosthesis.

Polycentric knees offer yet another biomechanical advantage - additional toe clearance at mid-
swing. The actual ground clearance can increase as much as 3cm for some knee designs, thus
significantly reducing the risk of tripping on environmental obstacles.

Because of these biomechanical advantages, polycentric knees are widely prescribed. Many
clinicians advocate their use over friction-brake stance-control components when added stability
is desired. Polycentric knees also work very well bilaterally, providing stability without
preventing voluntary knee flexion under partial weight bearing.

Recently developed complex polycentric knees featuring five-, six-, or seven-bar linkages offer
more stance-phase functions than four-bar designs, such as a geometric lock that automatically
engages and disengages during ambulation. Some provide a limited range of controlled knee
flexion during the loading response phase of the gait, simulating this shock-absorption motion of
the biologic knee. Gait studies have confirmed that these knees result in a more biomechanical
normal gait pattern.

MI/Prosthetics manual/BPO/LLP/Aug 2009

 Fig.9.10 The centre of rotation changes during the different phases of the gait.

The disadvantages of this joint are that it is

expensive, it is difficult to repair and it is
often heavy.

9.5 Cosmesis

For the endoskeletal shank, making a

cosmesis is the same as for the transfemoral
prosthesis, refer to that manual for further
details.

When external joints are being used, the

rigid shank part provides the cosmesis.
However, there is a problem because there
will always be a gap between the shank and
the socket when the knee joint is flexed. The
extra width of the prosthesis is also a
problem.
Fig. 9.11. The four-bar knee holds up
underneath the thigh section and improves
sitting cosmesis.

MI/Prosthetics manual/BPO/LLP/Aug 2009

9.6 Knee Disarticulation
Practical Projects

Materials and components

The ICRC transfemoral knee joint can be

used if the socket attachment area
is cut down.

The advantages of using the trans-femoral

knee joint are that it is very strong and easy
to adjust.

The disadvantages are that the knee center

will be too low when compared to the sound
side.

MI/Prosthetics manual/BPO/LLP/Aug 2009

Panel Opening

1. Description

2. Suspension

3. Assessment

4. Cast taking

5. Rectification

6. Fabrication

7. Alignment

8. Fitting

MI/Prosthetics manual/BPO/LLP/Aug 2009

Push Fit Liner

1. Description

2. Suspension

3. Assessment

4. Cast taking

5. Rectification

6. Fabrication

7. Alignment

8. Fitting

MI/Prosthetics manual/BPO/LLP/Aug 2009

External joints with side
steels
The main advantage of using external joints
with side steels is that the correct anatomical
position of the knee joint can be attained.
The disadvantages are that M-L cosmesis is
poor, the joints are heavy, and the alignment
is difficult to adjust.

1. Description

2. Suspension

3. Assessment

4. Cast taking

5. Rectification

6. Fabrication

7. Alignment

MI/Prosthetics manual/BPO/LLP/Aug 2009

 Chapter 10
Prescription Principles
10.1 Introduction A careful assessment of patient's stump
condition, general health, muscle strength,
The main areas to consider when forming
joint range of motion, and activities, are
the prescription for the knee disarticulation
needed to form the best prescription. It is
patient are socket design, suspension,
important to remember that every patient is
material selection, and component selection.
different and has different needs.
MATERIALS
10.2. Options o Polypropylene
o GRP
o Pelite
SOCKET o Leather
o End bearing
o Ischial bearing
o Panel opening KNEE JOINT
o Push fit o Single axis knee joint
o Leather lacing o Polycentric knee joint
o External joints with side steels
SUSPENSION
o Supracondylar FOOT
o Silesian belt o SACH
o Other o Single-axis
o Multi-axis
o Energy recovery
SHANK
o Endoskeletal
o Exoskeletal
Weight-Bearing: End-Bearing Non-End-Bearing
Socket Type: Oval/Short Socket Modified Quadrilateral Socket
Quadrilateral Socket
Socket Design: Panel Opening Panel Opening Panel Opening
Push Fit Push Fit Push Fit
Lacing
Suspension: Self-suspension Self-suspension Conventional /
o Supracondylar o Supracondylar Additional suspension
Additional Additional o Silesian Belt
suspension suspension

MI/Prosthetics manual/BPO/LLP/Aug 2009

 Socket design:

10.3 Case studies Suspension:

The following are some examples of
different patients with different stump
Shank:
conditions.

Discuss in your group and formulate an

Materials:
appropriate prescription for the below given
cases. Consider especially on the following:
Knee joint:
o What type of socket design and
suspension would you choose for
each patent?
Foot:
o Would you use exoskeletal or
endoskeletal design?
o What materials would you choose?
Special considerations:
o What type of knee joint would be
best?
o What type of foot would you
choose?
o Are there any special considerations Patient # 2
that would influence your design of
the prosthesis? The patient is a 35 year old healthy male
o What are the reasons for your with a right knee disarticulation amputation
decisions? due to a motorcycle accident when he was
30 years old. Muscle strength and joint
range of motion are normal. The patient
Patient # 1 spends long days in the market selling fruit
but he has a helper for carrying heavy
The patient is a 24 year old healthy male containers of fruit. The ground around the
with a right knee disarticulation amputation market is very uneven. His stump has firm
due to a land mine injury when he was 20 tissue but the scar is atrophic. The skin
years old. Muscle strength and joint range of covering the distal end is very thin, and
motion are within the normal range. The there are bony prominences on the end of
patient is a rice farmer and works very hard the stump that are painful when palpated. He
in wet conditions. He also likes to play cannot bear weight on the end or the stump.
sports. His general stump condition is very The stump can tolerate pressure above the
good. The stump tissue is firm. There is no femoral condyles.
problem with the scar. There are no painful,
bony areas. The stump is fully end bearing.
The stump can tolerate pressure above the Socket design:
femoral condyles.

Suspension:

MI/Prosthetics manual/BPO/LLP/Aug 2009

 Knee joint:
Shank:

Foot:
Materials:

Special considerations:
Knee joint:
Patient # 4
Foot: The patient is a 56 year old male with a
recent right knee disarticulation amputation
due to vascular disease. The stump is now
Special considerations: healed and he has come to be fitted with his
first prosthesis. He is in a weakened
condition because it took a long time for his
stump to heal after surgery. His family takes
care of him at home. He wants be to be able
to visit his neighbors near his home and go
Patient # 3 to temple once a week. The muscles of his
lower limb and range of motion on the
The patient is a 29 year old healthy female sound side are within normal range but the
with a left congenital knee disarticulation hip flexors and extensors on the amputated
amputation. Muscle strength and joint range side are grade 4. He has a 5 degree hip
of motion are normal. The patient is an flexion contracture on the amputated side.
office worker and cosmesis is very The stump is now well healed. There are no
important to her. The length of the femur on painful areas but there is still some edema.
the amputated side is five centimeters
shorter than the femur on the sound side.
The stump tissue is very soft and fleshy Socket design:
proximally and also above the condyles.
There is no problem with the scar. There are
no painful, bony areas. The stump is fully Suspension:
end bearing.

Shank:
Socket design:

Materials:
Suspension:

Knee joint:
Shank:

Foot:
Materials:

MI/Prosthetics manual/BPO/LLP/Aug 2009

Special considerations

MI/Prosthetics manual/BPO/LLP/Aug 2009

 Chapter 11
Alignment Procedures

11.1 Bench Alignment 2. Knee stability

The knee disarticulation prosthesis can be TKA line
treated as a prosthesis for a long
transfemoral stump. The basic concepts of The TKA line should fall 5mm anterior to the
bench alignment are the same, although knee joint axis for stance phase stability. If
there are some minor differences. The areas the patient has weak hip extensors, the
to look at are: distance can be increased for more stability.
1. Socket angles
3 Knee joint height
Flexion
Knee joint height should be mid way between
Usually no socket flexion is needed in bench the medial tibial plateau and adductor tubercle
alignment. This is because the knee level (or 1.5-2cm proximal to medial tibial
disarticulation stump has a long lever arm plateau level).
and the hamstrings as well as the gluteus
maximus can exert a strong extension 4 Knee joint rotation
moment to stabilize the knee during stance
phase. A small amount of socket flexion External rotation 5 degrees in reference to the
should be used for the patient who has weak line of progression.
hip extensors. Flexion angles will need to be
adjusted for patients with hip flexion
contractures.
5 Foot rotation
It must be noted that a small flexion angle at
External rotation 5 degrees in relation to the
the hip will result in a large shift toward the
line of progression.
anterior of the distal end of the stump. This
will have implications for the TKA line and
stance phase stability.
6 Plumb lines
Abduction /Adduction
Posterior: Middle of socket - Middle of knee -
The abduction/adduction angle of the stump Middle of heel
should he carefully measured during
assessment. Plumb lines should be drawn on Lateral: Middle of socket - Anterior to knee -
the cast, transferred to the socket and A third along foot from heel
followed during bench alignment.

MI/Prosthetics manual/BPO/LLP/Aug 2009

11.2 Bench Alignment for 2. Exoskeletal shank
External Side Bars The exoskeletal shank should match the shape
and size of the patient's sound limb. The
1. Socket shank will be hollow and the distal end of the
socket must fit accurately into the proximal
External Joints cannot be used with a panel area of the shank for good cosmesis and so
opening socket, a push fit socket must be that the joints flex easily without the socket
used. rubbing the shank.
An ankle block is molded into the shank
Rounding the distal end pad before draping during draping for foot attachment. Concave
will give better cosmesis. and convex disks can be added so that foot
alignment can be adjusted. Special attention
should be paid so that the shank is the proper
length.

A common production method is to cast the

leg of a person whose leg closely resembles
that of the patient's. The cast is adjusted and
polypropylene can then be draped over the
cast to form the shank.
Another method is to measure and cast the
patient's sound leg and then change the shape
of the cast using the measurements.

Fig. 11.1 Push fit socket.

Fig. 11.2 Exoskeletal shank.

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3. Positioning the socket with Figure 11.3 shows positioning of the socket
and shank from the lateral view. Figure 11.4
the shank shows positioning of the socket and shank
from the posterior view.
An easy way to position the socket on the
shank for joint alignment is to fit the socket The socket must also follow the line of
into the proximal part of the shank and then progression in relationship to the shank and
tape them securely together with masking foot in the transverse plane. This will be
tape. Special attention should be paid to easiest to do if you have flattened the
proper flexion, abduction/adduction and proximal medial wall of the socket so that it is
rotation of the socket in relationship to the parallel to the line of progression or if you
shank. The socket will be more stable in the have transferred the progression line to the
shank during joint alignment if the posterior distal end of the socket.
section of the shank is not trimmed until the
final stages of production. When the socket and shank have been
securely taped together, draw lateral and
posterior plumb lines on the midlines of the
prosthesis for reference.

Fig.11.4 Socket and shank alignment, posterior

Fig.11.3 Socket and shank alignment, view.
lateral view.

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4 Knee joint and side steel
alignment
Alignment of knee joints and side steels
must follow the following criteria:
o The knee joints must be located
approximately 1.5-2.0cm above
MTP.
o The knee joints should be located
5mm posterior to the anatomical
knee center.

Fig.11.6 Knee joints parallel to plumb line and

each other

o The knee joints should be externally

rotated 5 degrees from the progression
line.
o The knee joints should be parallel to
each other in the transverse plane.

Fig.11.5 Knee joint placement 1.5-2.0cm above

the medial tibial plateau (MTP) and 5mm
anterior to anatomical knee joint centre.

o The knee joints must be located at

the same height from the floor.
o The knee joints should be parallel to
each other.
Fig.11.7 Knee joints 5 degrees externally rotated
and parallel to each other.

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11.3 Static alignment holding onto the rails.

8. Check the height of the prosthesis first.

Static alignment for the knee disarticulation
Ask the patient to stand with the feet
patient is similar to that of patients with
about 10 cm apart and with equal weight
other levels of amputation but the basic
on both feet. Adjust the height until the
procedures will be reviewed here.
pelvis is level.
Static alignment is done with the patient
9. When the prosthesis is the correct height,
standing only. The purpose is to make sure
make a very careful assessment of the fit
that walking with the prosthesis is possible
of the socket. Check the weight bearing
and safe. The three main areas to check are
areas, the suspension, and the trim lines.
fit of the socket, length of the prosthesis and
Look for any gaps in the fit of the socket.
alignment.
10. If the socket fit is satisfactory, check
PROCEDURE alignment. Make sure that the knee is
stable. Make sure that the foot is flat on
1. Watch the patient walking with the old the floor. Check knee rotation and toe-out.
prosthesis if he or she has one. This will Make sure that you step back from the
tell you if there is anything unusual or patient to get a total view of the whole
wrong with the patient's gait habits. person from the front and back and from
Look at the sound leg as well since the side. Do not only look at the different
problems with the sound side will also parts of the prosthesis.
affect the gait.
11. Make sure that the patient feels
2. Review the information on the comfortable in the prosthesis. When
measurement and assessment charts. everything is satisfactory, the patient can
Check the patient again and make begin walking and dynamic alignment can
yourself familiar with the problems. begin.
3. Check to see that the prosthesis matches
the prescription.
11.4 Dynamic alignment
4. Check to see that bench alignment is
correct. Gait deviations of the knee disarticulation
patient and the procedures for checking and
5. Examine the patient's stump carefully to correcting them during dynamic alignment are
see if there have been any changes since the same as those for a transfemoral patient
the last visit. Note any cuts, abrasions, with a long and strong stump.
edema or other problems.
6. Help the patient to put on the prosthesis. Please refer to the Transfemoral Prosthetics
At this time you can begin checking to manual for further detail.
see if the socket is too tight or too loose.
The main differences will be adjusting
7. If there are no problems with putting the alignment with the modified ICRC
prosthesis on, ask the patient to stand. transfemoral knee joint or with external joints
This should be done between walking with side steels.
rails so that the patient can stabilize by

MI/Prosthetics manual/BPO/LLP/Aug 2009

 Chapter 12
Checkout Procedure

12.1 Introduction The patient should not be allowed to take

the prosthesis home if any problems are
found during checkout procedure.
It is important to go through a careful
o Remember, a badly fitting prosthesis
checkout procedure of the knee
or a prosthesis which is too difficult
disarticulation prosthesis before the patient
to use will probably not be used after
can take it home. This will ensure that all the
a very short time, so you and patient
work which has been done up to this point
may have wasted your time and
has been correct.
energy.
The checkout procedure ensures:
The prosthesis is evaluated with the
o no mistakes in the production of the
patient standing, walking, sitting and
prosthesis
with the prosthesis removed from the
o the patient has no unexplained gait
stump, similar to the pattern of other
deviations
prosthetic checkout procedures.
o the patient is able to use the
prosthesis
o the patient knows how to clean and
maintain the prosthesis 12.2 Procedure
The prosthetist and physiotherapist must
work together and make sure; 1. Let the patient put on the prosthesis
o enough gait training has been given without your help. Make sure that the
so that the patient can get the best patient knows how to position it
possible use of the prosthesis. correctly.

The patient should also be taught: 2. With the patient standing check:
o how to recognize problems with the o Length of the prosthesis
socket fit and function of the o Socket fit for comfort,
prosthesis. suspension and trim tines
o how to adjust fit with socks
o when to stop wearing the prosthesis 3. Let the patient walk for a little while
and contact the centre. and then check:
o that they are always welcome to come o Alignment. If there are any
back to solve any problems. gait deviations you need to
As a prosthetist, you are very important find the reason for them and
part of the patient's life and they depend correct them if possible
on you. o Comfort and effort needed by
o Always welcome the patient as if they the patient to walk
are a family member, no matter what o Ability to walk on
the problem. slopes/stairs/rough ground.
o Cosmesis

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 Chapter 13
Common Socket Problems

13.1 Introduction
The bulk of this chapter will deal with an end bearing socket design. This may incorporate
either a modified quadrilateral brim or an oval shaped socket.

If a patient cannot bear weight on the distal end of the stump, then they will be fitted with a
standard quadrilateral socket. The problems that may be encountered in the proximal section
of this type of socket are covered in detail in Transfemoral Prosthetics. However distal
problems are unique to the Knee Disarticulation prosthesis.

13.2 Proximal problems

1 BRIM IS TOO LARGE

The brim should be a close fit with the proximal tissues, and in this way allow for comfort
and control of the prosthesis. If the fitting is loose, then the patient will experience
discomfort due to friction and localized pressure. It is difficult to adjust the fitting with socks,
as the distal end of the stump is bony and the addition of socks can produce intolerable
pressure over this area.

One temporary solution is to add pads of EVA to the proximal section, best placed anteriorly
and on the lateral side. The best solution is to produce a new socket.

2 BRIM IS TOO SMALL PROXIMALLY

If the brim is too small proximally, it can cause congestion in the stump and may lead to an
adductor roll. It may also prevent the patient from fully entering the socket and thus not
achieve end bearing.

Check that the patient is not wearing too many socks, or socks that are too thick. (Usually the
patient will also feel distal discomfort if wearing too many / too thick socks)

The only solution to this problem is to make a new socket.

3 SOCKET IS TOO SMALL PROXIMALLY

Usually if the socket is too small proximally the tissue simply plug fits into it. The patient
simply bears weight not on the distal end but more proximally on the soft tissue. This will be
uncomfortable. The prosthesis will appear to be long because the stump is not all the way
down in the socket.
Check that the patient is not wearing too many socks, or socks that are too thick. (Usually the
patient will also feel distal discomfort if wearing too many / too thick socks)

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The only solution to this problem is to make a new socket.

4 MEDIAL WALL
The symphysis pubis should be located very close to the brim of the socket but not in contact
with it. It is sensitive to pressure and will cause a great deal of pain if loaded. Loading on this
area means that the medial wall is too high. (Remember that the stump is end bearing, so it is
not possible to “fall” into the socket.)

Reduce the height of the medial wall by cutting it down. Ensure that there is a flare out to
reduce localized pressure during stance phase. The medial wall should be kept as high as
possible within 5 cm below the perineum.

4b Adductor rolls
Adductor rolls are caused by problems at the medial wall, either a wall that is too low
or the dimensions of the socket are too small. It is important that adductor rolls are not
allowed to continue long term as they become hard and will cause discomfort for
subsequent correct fittings.

The only solution for either cause is to produce a new socket.

5 POSTERIOR WALL
In an endbearing socket there is no need for the ischium to be located on the ischial seat, and
in the case of supracondylar suspension, should not be in contact.

5b Seat is too wide

If the width of the seat is excessive to the medial side, then it will rub against the other
buttock.
If the seat is too wide to the posterior it will push the socket into the stump when
seated.

The seat can be trimmed as long as some material is kept to act as a flare out.

6 ANTERIOR WALL
This must be low enough to allow the patient to sit comfortably. The edge of the socket will
hit the anterior area of the ilium if it is too high when the patient sits. The patient should be
able to sit comfortably with the hip flexed at 90 degrees. In an end bearing socket there is no
need for a counterforce to keep the ischium on the seat, and thus the wall can be reduced in
height.
Incorrect edge shape leads to high pressure. The edge should be flared out enough to ease the
pressure but should not cause a gap.

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6a Antero-Medial corner
Discomfort and pain in the anterior medial corner of the socket can be caused by a lack of
relief for the adductor longus tendon. Before socket modifications are considered, we should
check to see if the patient has donned the prosthesis correctly. If the pressure is caused by the
socket, then an attempt should be made to create relief, either by heating the socket and
pushing it out, or by grinding away material from the soft liner / socket.

7 LATERAL WALL
The most common problem with the lateral wall is gapping. The gap is caused by the M-L
diameter of the socket being too large.

A temporary solution to this problem is to add EVA pads to the lateral wall in the area of the
gaps, but the best solution is to make a new socket.

Excessive pressure on the trochanter is usually a result of a trim line that is too low. If the
socket wall is too low then the edge will dig into the trochanter.

The only solution is to make a new socket with higher lateral trimlines.

8 PAIN
Pain can be caused for a variety of reasons, usually as a result of excessive pressure. Bone
spurs, bursas and neuromas can also be responsible.

This can be done by adjusting the socket or liner over the area causing the problem, either by
heating and pushing out or by grinding.

9 SKIN BREAKDOWN
Excess pressure causes skin breakdown and the only cure is to relieve the pressure. This can
be done by adjusting the socket or liner over the area causing the problem, either by heating
and pushing out or by grinding. It is important that you advise the patient to not wear the
prosthesis until the wound has healed.

If the skin breakdown is caused by rubbing, this is usually due to the socket being loose. The
fit of the socket can be improved by adding EVA pads, but should only be a temporary
solution, while a new prosthesis is being produced.

13.3 Distal end

The distal end has a number of bony prominences that cannot be loaded. Excessive load will
cause skin breakdown. Pressure on these areas will need to be relieved by grinding or heating
the socket.

However, if the relief for the bony areas is excessive, the stump will be allowed to move. This
will cause friction damage to the skin in the form of abrasion or blisters.

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The effect of too much pressure is easily confused with the effect of too little pressure. In the
case of an open ended socket that is too tight the symptoms may look the same. The end of
the stump can become inflamed, red and hot. This is called congestion.

Congestion is the collection of fluids in the distal end. Because there is no total contact the
venous return can be reduced. As the fluids gather, the pressure in the soft tissue increases
making it more difficult for oxygenated blood to enter the tissue. It is corrected by changing
the socket fit.

Total contact at the distal end and an increase in the diameter at the mid- stump area will
increase the blood flow back out of the stump.

13.4 Supracondylar area

Excessive pressure can cause the skin to be damaged and restrict blood flow leading to
congestion.
If the supracondylar pressure is too distal it will impinge on the femoral condyles and cause
pain.

Both will require the socket / liner to be relieved by heating or grinding.

If the supracondylar pressure is too loose the stump will piston in the socket leading to
friction damage and socket instability.
Pressure too proximal allows pistoning, as the socket will drop onto the condyles, and then is
pushed back up again when the foot is in contact with the ground.

Both will require that the liner be built up in the correct location, or the socket heated and
pushed in.

13.5 Volume changes

By far the most common problem is that of volume change. If the patient gains weight the
stump will increase in size. In that case the only solution is a new socket. The patient will no
longer fit into the socket. An adductor roll may form. The patient will not be comfortable.

If the patient loses weight and the stump shrinks, the socket can be adjusted by adding
anterior wall pads. If the reduction is temporary, in the case of a short illness, then this is a
good solution. If the reduction is permanent, as in the case of a primary patient, then a new
socket is the answer.

It is difficult to adjust the fitting with socks, (as in a TF socket) as the distal end of the stump
is bony and the addition of socks can produce intolerable pressure over this area.

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13.6 Skin problems
Because the skin is contained in a closed space in a hot climate, many patients will get skin
problems. Bacteria grow very well in a hot humid environment.

The best way to avoid skin problems is to wash the stump several times a day and dry it well.
Clean skin is healthy skin. Also each time clean and dry socks should be used. If the patient
sweats a lot, they should change their socks many times a day.

Small infections can easily get worse and cause a great deal of pain. In some cases the
infection can cause illness and even lead to further amputation. Infections and sores are
treated by antibiotics and rest. The patient should take off the leg until healed. The patient
should keep the stump wrapped and elevated to prevent edema. The fit of the socket should be
checked before wearing again as the size of the stump may have changed.

13.7 Rotational problems

In some cases rotational instability will be seen with the self-suspending knee disarticulation
prosthesis. This is often caused when the stump tissue is soft and tends to rotate around the
femur. Medial or lateral whips may be seen. Rotation of the foot at heel strike may also be
seen. In these cases, the addition of a Silesian belt can help control this type of rotational
problem.

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