Transfemoral Prosthesis Suspension system Socket Design

1. TRANSFEMORAL AMPUTATION
AND
ITS PROSTHETIC MANAGEMENT
Definition
Amputation of the lower limb between the hip joint and
knee joint commonly referred to an above-knee amputation.
Causes or Indication of Transfemoral Amputation 
1. Vascular disease or Diabetes Mellitus
2. Trauma
3. Bone Infection
4. Bone tumors
Ideal length of the above-knee stump
❖ Ideal length of the stump – 10 from greater trochanter.
❖ Minimum length of the stump – 5 from greater trochanter.
❖ Maximum length - 4 above from knee joint.
Note  In
• Long above knee amputation – 55 to 75 of normal femur.
• Medium above knee amputation – 35 to 55 of femur is present.
• Short above knee amputation – groin t 35  of femur is present.

2. Advantages of transfemoral amputation
1) Healing rate is greater than for more distal amputation.
2) The residual limb in many cases is easier to fit with a socket.
3) Longer stump is equal to better control and less surface
pressure.
4) Few bony prominences and less problem of socket
adaptation.
Disadvantages of transfemoral amputation
1) Mortality rate is greater for proximal amputations.
2) More surgical complications.
3) Cut muscle bellies, retract, atrophy and lose their function,
myoplasty will prevent this problem.
4) Rehabilitation for prosthetic walking is less successful than
with moral distal amputations.
5) No end – bearing possibilities as in knee disarticulations.
6) Need of a suspension(suction or belt).
7) Mobility is reduced – increased energy is needed during gait.

3. PROSTHETIC MANAGEMENT OF
TRANSFEMORAL AMPUTATION
POST OPERATIVE IMMEDIATE PROSTHESIS (POIP)
❖Only selective amputate will receive this type of prosthesis which are
directly molded on the stump. They are provided within 24 hrs. of
amputation. They are often referred as Immediate Post Surgical
Fitting (IPSF). This prosthesis is for younger, healthier individual
undergoing amputation due to tumor, trauma or infection.
❖In general, earlier the prosthesis is fitted, it is better for the amputee.
PROSTHESIS
POST OPERATIVE
IMMEDIATE
PROSTHESIS
INITIAL
PROSTHESIS
PREPARATORY
PROSTHESIS
DEFINITIVE
PROSTHESIS
ENDOSKELETAL
PROSTHESIS
EXOSKELETAL
PROSTHEIS

4. ❖One of the most difficult problems facing the amputee and the
treatment team is edema, or swelling due to the accumulation of the
tissue fluid.
❖It is important to fit the prosthesis as soon after the surgery as
possible to combat edema.
❖They provide protection from accidental injuries.
❖Allows the patient to begin with controlled weight – bearing.
❖ It helps in improving wound healing.
Advantages
• Helps in getting rid of phantom sensation.
• Helps to maintain good range of motion
• Helps amputees to remember the walking pattern.
• Boost the moral of amputee when they see themselves walking.

5. INITIAL PROSTHESIS
▪ It is provided as soon as the sutures are removed.
▪ It is sometime referred to as Early Post Surgical Fitting (EPSF).]
▪ This can be prescribed after 4 weeks of amputation.
▪ Generally, EPSF is directly molded on the stump by pop bandage
or fiber glass bandage.
▪ This prosthesis is prescribed to prevent the patient’s muscles goes
into atrophy.
PREPARATORY PROSTHESIS
• It is referred to as temporary prosthesis.
• A temporary or preparatory prosthesis is used for weeks or
months until the stump has stabilized before the permanent or
definitive prosthesis is provided.
• The socket may made of either POP or a plastic material.
• The temporary prosthesis is endoskeletal and cannot be
exoskeletal.

6. DEFINITIVE PROSTHESIS
• This type of prosthesis is not prescribed until the stump has
stabilized.
• The average life span of this type of prosthesis is 3 – 5 years.
• Mostly these are replaced due to change in stump volume from
atrophy, weight gain or weight loss.
• Can be Exoskeletal or Endoskeletal.
• The major components are the suspension system, the socket,
shanks, and the prosthetic foot.
ENDOSKELETAL TF
PROSTHESIS
EXOSKELETAL TF
PROSTHESIS

7. SUSPENSION SYSTEM FOR
TRANSFEMORAL PROSTHESIS
Importance of suspension in prosthesis
It helps to stabilize the prosthesis during ambulation.
Suspension system of tf
prosthesis
Silesian Belt Suspension
Total Elastic Suspension Belt
Hip joint with Pelvic Band
Suspension liners with shuttle
lock systems
Gel liners/Suction liners with
Lanyard System
Traditional Suction suspension
system

8. 1. SILESIAN SUSPENSION BELT
It is usually made from leather or
lightweight webbing.
❖Attachment:
• It is attached to the lateral
aspect of the socket, encircles
the pelvis, and then runs
through a loop or buckled on
the anterior of the socket.
❖Indications:
1. Auxiliary suspension required.
2. Rotational and coronal movement control required.
3.Added security during ambulation.
❖Advantages:
1. Easy to don and doff.
2. Provides increased coronal and rotational control.
❖Disadvantages:
1. Limited cosmesis.
2.Inherent pistoning present.

9. 2. TOTAL ELASTIC SUSPENSION
BELT
It is typically made of an elastic neoprene
material.
❖ Attachment:
• The distal sleeve of the TES belt fits snugly around the
proximal half of the thigh section of the transfemoral
prosthesis.
• The neoprene belt encircles the waist and attaches in
front with Velcro.
❖Indication:
1. Auxiliary suspension is required.
2. Rotational and coronal control required.
3. Added security during ambulation is required.
❖Advantages:
1. Easy to don and doff.
2. Good physiologic aid for those wearing suction suspension.
3. Provides increased coronal and rotational control.
❖Disadvantages:
1. Limited cosmesis.
2. Inherent pistoning present.
3. Body heat retention and hygiene, may be uncomfortable because of
constriction around the waist.

10. 3. HIP JOINT WITH
PELVIC BAND
The pelvic belt is made
of leather and attached
to the prosthesis by
means of a metal hip joint.
❖ ATTACHMENT:
• Pelvic belt passes between iliac crest and the greater trochanter of each
hip and a joint that is positioned slightly above and ahead of the greater
trochanter.
• The joint is placed over the anatomical hip joint
• The pelvic belt consists of a 2 wide metal pelvic band attached to the
joint, which extends from the PSIS to a point 1 medial to the ASIS.
❖ INDICATION
1. Maximum medial – lateral control needed.
2. Easy donning required.
❖ ADVANTAGES:
1.Easy to don and doff.
2. Provides good swing phase control.
3.Provides increased medial – lateral stability.
❖ DISADVANTAGES:
1. Poor cosmesis due to bulk.
2. Inherent pistoning present and it is heavier.

11. 4. SUSPENSION LINERS WITH SHUTTLE
LOCK SYSTEM
It generally made of silicone, polyethylene, etc.
This liner is commonly called a locking liner.
This liner has an external distal cap, the center
of which a separated pin screws into and sticks out
approximately 1.5.
How to wear and remove the liner?
The pin engages into the shuttle lock, inside the bottom of the socket, when
the individual stands and pushes his or her limb down into the socket.
To remove the prosthesis, the individual depresses a release button on the
medial aspect of the socket that disengages the serrated pin.
❖INDICATION:
1. Moderately stable volume.
2. Scar tissue or skin grafts on residual limb.
3. Good hygiene and good upper extremity strength.
❖ADVANTAGES:
1. Cushions residual limb from socket liners.
2. Allow some accommodation for volume fluctuation.
3. Provides torque absorption.
❖DISADVANTAGES:
1. Can be difficult to don.
2. Has limited durability.
3. Must be cleaned daily to prevent dermatological issues.

12. 5. GEL LINERS WITH LANYARDS SYSTEM
▪ MECHANISM-
• This system uses locking liners, but instead of a pin screwed into the
liners distal cap, a lanyard (cord or strap) is attached to the cap and
routed through distal socket and used to pull the residual limb into
the socket.
• The lanyard is then attached to the external lateral aspect of the
socket via locking hook or using Velcro.
▪ INDICATION
1. Moderately stable limb.
2. Stable volume.
3. Good upper extremity strength and balance.
▪ ADVANTAGES
1. Cushions residual limb from socket liners.
2. Allow some accommodation for volume fluctuation.
3. Provides torque absorption.
▪ DISADVANTAGES
▪ Can be difficult to don.
▪ Has limited durability.
▪ Must be cleaned daily to prevent dermatological issues.
▪ Can add thickness to the width of the prosthesis.

13. Traditional suction suspension system
❖ MECHANISM:
▪ Traditional suction suspension is
accomplished by surface tension, negative
pressure and muscle contraction. The direct
skin fit reduces pistoning between the residual limb and
socket; increases proprioception.
❖ Application of a traditional suction suspension
A suction prosthesis can be donned in several ways:
1. One option uses donning sock (of cotton stockinet), donning
sleeve (of parachute nylon), or elastic bandage to pull the
residual limb down into the socket.
a) Once the limb is well seated in the socket, the sock,
sleeve or elastic bandage is pulled through the valve
located at the anterio – medial distally to the socket, and
the air expulsion valve is then screw back into the place.
b) This process requires considerable agility and
balance on the part of the wearer.
2. Second option is to add lubricant to the skin (e.g. liquid
powder) to facilitate the residual limb sliding into the socket.
The air expulsion valve is then “burped” by pushing or pulling
the valve button, to release any trapped air. The liquid dries
quickly and suction is achieved.

14. ❖ INDICATIONS
1.Medium or long residual limb.
2.Stable volume.
3.No severe scarring.
4.Good upper extremity strength and good balance.
5.No cardiovascular issues.
❖ADVANTAGES
1.Promotes increased proprioception due to more
intimate fit.
2.Have no straps or belts.
3.Positive – negative pump providing positive suspension
during stance and negative suspension during swing
phase.
❖DISADVANTAGES
1.Can be difficult to don.
2.Can be hot.
3.Individual must maintain a stable residual limb volume.

15. SOCKETS USED IN TRANSFEMORAL PROSTHESIS
What is the use of socket in prosthesis?
• A socket creates a means of containing and
interfacing with the residual limb to transfer
forces from the skeleton to the prosthesis.
TYPES OF SOCKETS USED IN TRANSFEMORAL
PROSTHESIS
1.Plug fit socket
▪ Prior to the 1950s, prosthetist typically carved a “plug fit”
socket from a block of wood.
▪ A functional benefit of the socket depends on the skill of the
craftsman.
▪ It was often uncomfortable and cumbersome while walking and
sitting.
▪ The plug socket was crafted to contain the remnant thigh
muscles, support body weight at the groin level (below the
ischium), and was often open ended to eliminate distal limb
contact.

16. 2. QUADRILATERAL SOCKET
It was designed by C.W.Radcliffe and J.Froot at the
University Of California At Berkeley in the early 1960’s.
INDITICATION
1. Less active and geriatric patients.
2. Patient with good muscle tone.
3. Patients with long residual limbs and grater adductor
control.
As the name implies, the quadrilateral socket consists of four
walls. These are referred as the anterior, posterior, medial and
lateral walls. Each wall has its specific functions.

17. ANTERIOR WALL:
• The anterior wall blocks forward motion of the residual limb.
• The anterior brim rises 2.5 inches above the ischial seat.
• If anterior wall is too high, it has an effect on the abdomen or the
anterior superior iliac spine (ASIS).
• The anterior medial corner contains a channel or relief for the
adductor longus and gracilis tendon.
MEDIAL WALL:
•The function of medial wall is to contain tissues medially and to
provide counter pressure to the lateral wall.
•The proximal brim is horizontal and parallel to the floor and the
distal end is contoured for total contact.
•The height of the medial brim is usually the same as that of the
posterior wall, to prevent an adductor roll.
•If an adductor roll occurs, the quadrilateral socket gets enlarged
below; the top of the medial wall to accommodate the adductor
roll.
MEDIAL BRIM:
• The brim of the medial wall is horizontal and at the same height
as the posterior brim. if there is marked tissue redundancy, the
medial brim maybe slightly lower than the posterior brim but no
more 0.3 to 0.6cm (1/8 to 1/4). The socket should not press on
the pubic ramus.

18. LATERAL WALL:
•The function of the lateral wall is to provide a surface against
while the lateral femur may push to stabilize the hip in the
stance phase.
•The lateral force of the femur is responsible for the medio –
lateral stability of the pelvis. As with any lever system, the longer
the lever arm the greater the moment generated and that
results in less pressure. Therefore a shorter residual limb may
have a higher lateral wall in an effort to provide enough surface
areas for stability.
POSTERIOR WALL
•The inner surface o the posterior wall of the socket is a flat
surface that slants anteriorly as it goes distally so the limb is set in
initial flexion.
•Below the brim, the socket is contoured for the hamstring
muscles.
•The posterior wall provides the surface against which the limb
pushes to keep the trunk erect and to maintain knee extension.
•The outer surface of the posterior wall is flat to prevent rolling so
that the wearer may sit in a stable manner.
•The exterior is padded to protect the socket surface, absorb the
sound of impact on a chair, and protect the wearer’s clothing
from friction against a chair.

19. POSTERIOR BRIM:
• The brim of the posterior wall is horizontal, parallel to the floor.
• The ischial seat, a thickening of the medial part of the posterior
brim under the ischial tuberosity, provides the major weight –
bearing area.
• Medially, the posterior wall slants upward and posteriorly so as
not to produce excessive pressure on the hamstring tendons.
• The lateral part brim of the brim, the gluteal shelf, contacts the
gluteus maximus for additional weight bearing and has a slanted
relief to permit gluteal bulging during walking.
• If the muscle is firm, the proximal posterior wall may flare as
much as 10, as little as 7 if it is soft.
Advantages:
•The casting procedure is well established.
• The fabrication procedure is standardized.
Disadvantages:
• Femur is difficult to hold in adduction due to the wider medial –
lateral dimension of the socket. Additionally the socket has
decreased lateral wall support.

20. PROBLEMS ASSOSCIATED WITH QUADRILATERAL SOCKET
1. Problem: tightness or “cutting” in the region of adductor longus
tendon.
Cause: improper relief/channeling in the anteromedial corner of the
socket; if medial AP dimension is too narrow, that have an
effect on ADL tendon, if medial AP is too wide causing ischium
to slide off seat into socket.
2. Problem: crouch pressure or burning sensation, ramus pressure
Cause:
• If medial AP dimension is too wide causing ischium to slide off
seat into socket.
• If socket is too large causing painful adductor roll; if there is
insufficient provision for existing adductor roll.
• If ML dimension is too small, it pushes ischium too far away
from medially and crowds adductors.
• If the superior brim of posterior wall slants considerably from
lateral to medial, ischium may slide medially during walking
and crowd adductors.
3. Problem: pinching in the posteromedial corner.
Cause: if there is insufficient radius of posterior and medial wall
juncture.
4. Problem: discoloration of distal residuum
Cause: if there is lack of total contact, usually along medial aspect.

21. 5. Problem: pain or pinching at medial superior brim
Cause: if there is inadequate flaring above and medial to Scarpa’s
triangle, which causing pubic crest to bear weight.
6. Problem: pinching in lateral two thirds when sitting or rising
Cause:
• If brim is too tight that can have an effect on ASIS; if pelvic belt
is worn, pinching is from the brim too low allowing flesh to be
caught between socket and belt.
7. Problem: numbness of residuum
Cause:
• If Scarpa’s triangle is too prominent that can cause pressure on
femoral artery.
• If brim of the socket is too low, that will produces a narrow
band of tightness across the anterior residuum.
8. Problem: pain at lateral distal residuum
Cause:
• If there is inadequate relief for distal end of femur; insufficient
adduction and/or improper contouring of lateral wall to
provide stabilizing surface proximal to distal end of femur.
• If ML dimension is too large at ischial level, causing socket to
shift laterally at midstance so the distal end of the femur
stabilizes against the socket.
9. Problem: pain at proximal brim
Cause: If there is insufficient relief for the greater trochanter

22. 10. Problem : burning sensation at the ischial tuberosity
Cause:
• New amputee unfamiliar to sensation;
• If there is insufficient radius on inner edge of ischial seat;
while sitting, excessive thickness of socket wall causing
posterior wall to push strongly on hamstring tendons while
ischium rests on chair.
• If medial AP diameter is too small which causing ischium to
be located too far posterior on seat and causing
compression of hamstring tendons.
11. Problems: pain in ischial tuberosity
Cause:
• If the socket is too large which results in failing to provide
sufficient support in other areas.
• If medial AP dimension is too wide, the ischial tuberosity will
be on forward edge of seat and slide over radius
• If posterior brim slopes downward from medial to lateral,
gluteal support will be minimal thus increasing load on
ischium.
12. Problem : discomfort lateral to ischial tuberosity
Cause: socket is too small, muscle bunching from contour of inner
socket, but usually due to insufficient hamstring relief.

23. RADCLIFFE’S PRINCIPLE OF LATERAL
STABILIZATION
The solution of the problem associated with quadrilateral
socket is to prevent the proximal socket
from shifting laterally by using ischial containment (also
called bony or skeletal lock). To understand this solution
properly it is best to start with Radcliffe’s principle of lateral
stabilization (1955). This may be followed as:
1. The weight of the amputee’s body, acting through the centre of
gravity, tends to cause the pelvis to dip towards the sound side
during stance phase on the
amputated side.
2. This converts the pelvis into a
lever with the supporting point,
lateral of the ischium, acting as
the fulcrum.
3. The tendency of the pelvis to dip
is resisted by the gluteus medius
exerting a counteracting moment
to the pelvic lever.
4. For the gluteus medius to work at
maximal physiological efficiency it

24. must e maintained closed to its normal rest length.
5. This is achieved when the femur at its normal position of adduction.
6. The lateral wall of the socket must be shaped to maintain the
position, anticipate the outward movement of the femur under load,
and to distribute the pressure comfortably.
7. As the result of these forces
acting against the shaft of the
femur laterally, a counter
pressure is created by the
medial brim of the socket
pressing against the stump so
that “pressure in the crotch
or medial area is then
predominantly lateral rather
than vertical”. That is to say,
a compressive force is
exerted by the medial wall
against the medial proximal
tissue of the limb.
8. This in turn creates a shearing
force in the soft tissues trapped between the medial brim of the
socket and medial structures of the pelvis.

25. ISCHIAL CONTAINMENT
SOCKET(IC)
❖ Newer design than the quadrilateral socket;
❖ The basic idea is to stabilize the pelvis and femur by controlling
the ischium and the femur.
Functional characteristics
1. Higher lateral wall
2. Low posterior wall
3. Ischial weight bearing
4. Reduced ML dimension
5. Total contact
6. Rigid or flexible
INDICATION
1.High active patient
2.Patients requiring positive ML stability
3.Short residual limb
4.Require greater control than a quadrilateral socket.
5.Patients with residual fleshy limbs that require greater
control.

26. Medial – lateral dimensions:
• The medial – brim of the IC socket is an oblique sloping
surface, upon which the ischium occupies area.
• To prevent the ramus from sliding laterally and
downward into the socket the prosthetist must
exaggerate the counter pressure from the lateral side.
This has been done by a reduction in the M – L dimension
particularly in the area just distal to the head of the
trochanter.
• The emphasis on the M – L dimension of the IC socket;
however, it has become clear at only a relatively late
stage that the dimensions at more than one level are
involved.
• Proximally the socket in that area at about the level of
medial brim must be enough to accommodate the bones
of the pelvis and the grater trochanter.
Anterior – posterior dimensions
• "The soft tissues must be accommodated. Therefore, the A-P
dimension is correspondingly increased as compared to
quadrilateral socket. Hence it can be seen that the major
dimensions of the IC socket are dictated by the imperatives
of ischial containment.
• Secondary, rationales for a wide A-P dimension have been
presented. It has been postulated that the greater A-P
dimensions of the IC socket better accommodate the major
muscle groups of the thigh, permitting them to function
more effectively.

27. • It has been suggested but never proven that a concentration
of pressure in the Scarpa's Triangle has a deleterious effect
on circulation in the distal tissues.
Above discussion helps to understood the necessity of allowing
sufficient room for functioning muscle groups. Regions of firm
musculature such as along the rectus femoris muscle are
channeled to avoid excessive pressure as required".
MEDIAL BRIM
• The desired to distribute the laterally thrust of the proximal
socket to the ischium has major implications for the shape of the
medial brim.
• The medial border of the ischium is to be loaded, while at the
same time the adductor longus tendon and pubic ramus, which
are not pressure tolerant and not to be loaded. Hence, the
medial brim is high enough posteriorly to bear against the ischial
ramus and dips lower as it passes anteriorly to clear the pubic
ramus and adductor longus tendon.
ANTERIOR BRIM
• The anterior brim of IC Socket is lower than the anterior brim of
the quadrilateral socket.
• The anterior brim may extend just proximal to inguinal ligament
or it may follow the inguinal crease.
• The actual height of the anterior brim varies with individual and
is limited by contact with bony prominences.

28. LATERAL WALL
• The most descriptions of IC socket describe them as extending
quite high above the grater trochanter and with a great deal of
contouring around the bony prominences.
• Whatever the socket styles, firm pressure and contouring in this
region posterior to the greater trochanter does more than
generate previously cited counter pressure.
• By compressing the gluteal muscle it helps to create gluteal
weight bearing, and by locking in around the greater trochanter
it plays a role in rotatory stability in the transverse plane.
POSTERIOR BRIM
• The posterior brim of the IC design is described as being located
4cm or so proximal to the ischial tuberosity so that ischium
inside the socket.
ADVANTAGES
1. Enhanced biomechanical stability created by the socket contact
with the medial aspect of the ischial tuberosity.
2. Provides greater biomechanical stability than the quadrilateral
socket.
DISADVANTAGES
1. Many variations of socket design exist due to lack of
standardization.

29. Cat- cam socket
❖ CONTOURED ADDUCTOR TROCHANTRIC –
CONTROLLED ALIGNMENT METHOD.
❖ It is discovered by John Sabolich.
EVOLUTION OF THE cat – cam SOCKET
• Quadrilateral socket have serious biomechanical problems.
o Poor transverse rotational stability.
o Lack of adequate stabilization in the frontal plane, which results in
the gluteus medius gait.
o In quadrilateral sockets, the ischial tuberosity is sitting on the top
of the ischial seat and is free to shift about. As the gluteus medius
pull the femur into abduction, the pelvic slides medially on the
ischial seat and make the abduction worse. The unsupported femur
has little choice than to drift into abducted attitude within the wide
M – L quadrilateral container.
o Pain at the distal femur and at the proximal medial area is due to
this abducted position and excessive soft tissue pressure medially.
Features of the socket
• This design includes undercutting of the trochanter and a special
fossa in which the ischial tuberosity and descending ramus can
rest, giving this bony prominence three dimensional support
within the socket.

30. • No more consideration is given
to the transverse angle of the
posterior wall relative to the
medial wall.
• The Scarpa’s triangle is virtually
eliminated, as are the adductor
longus and rectus channels and
ischial seat.
• Unlike quadrilateral socket, it
has large A – P and narrow M –
L.
CAT – CAM THEORY
The CAT – CAM holds the femur in adduction primarily by two means.
First,
• The ischial tuberosity and part of the inferior ramus of the
ischium rest inside the socket proper, and bear laterally directed
forces which work in conjunction with medially directed forces
borne by the femur.
• Medially directed forces bearing on the proximal portion of the
femur in the trochantric and sub-trochantric region act to hold
the ischial tuberosity on the inclined medial – posterior surface
within the socket, while forces on the mid and distal portion of
the femur act to maintain the roper adduction angle.
• The lateral surface of the socket proximal to the greater
trochanter is contoured intimately into the soft tissue distal of
the iliac crest.
• It is postulated that medially directed forces in this area, working
in conjunction with the medially directed forces on the lateral

31. surface of the femur and lateral directed forces borne by the
ischial tuberosity, create a three – point pressure system to lock
the femur into adduction and reduce motion that can occur
when the ischium is free to shift about.
Second,
• The narrow socket means that the pressure bearing areas of the
socket bear directly against the skeletal elements, thus reducing
motion lost through intervening soft tissues. A wide socket M – L
cannot provide this locking phenomenon since the femur can
fall away from the supporting surfaces.
• In transverse plane, the medially directed force of the ischial
tuberosity is posterior to the laterally directed fore of the
trochanter and femoral shaft.

32. Isny socket
• Its full form is Icelandic Swedish New York socket.
Features
• The ISNY system achieves the goal of enhanced patient comfort
by providing a thin, pliable, lightweight socket for tissue
containment.
• The thin socket allows better heat dissipation, increased sensory
input, and greater freedom for muscle activity as the socket
adapts to residual limb changes.
• The socket is easy and quick to form and modify, it nests in a rigid
laminated frame for weight transmission, and the translucence of
the vacuum-formed socket aids the prosthetist by served ad
check socket.
Socket Materials
For maximum benefit, the prosthetist should have a working
knowledge of the materials used in the supporting frame and the
thermoplastics used for the flexible socket, in order to provide a
maximally flexible, yet durable, system.
Two types of sheet thermoplastic are most commonly used to
vacuum – form flexible socket:
1. Polyethylene
2. Surlyn.

33. The basic characteristics of polyethylene and Surlyn may be
summarized as:
Characteristics Ethylux
Polyethylene
Surlyn
Moldability Relatively easy to mold Easy to mold
Strength Suitable for average
use
Suitable for heavy use
Edge finish Easy to finish Less easy to finish
Appearance Translucent transparent
Cost Inexpensive Expensive, triple the
cost of polyethylene.
SOCKET SPECIFICATION
• Segments of plastic, one square inch in area, were removed from
four areas of the socket:
o Mid sections of the posterior, anterior and lateral walls, as well
as the proximal – lateral wall in
the area of attachment of a
Silesian bandage.
• The average wall thickness for the
mid sections was 1.5 mm.
• The proximal – lateral wall was
thicker, approximately 22mm.

34. • The brim should be carefully rolled over the frame to insure
adequate socket – frame interlocking and to minimize the risk of
socket tear.
• Patient education regarding doffing the ISNY socket will also
extend socket life. The socket should not be doffed by putting
pressure on the proximal – lateral socket, as is the practice among
wearers of rigid suction sockets. Pushing stresses the anterior and
posterior corners, leads to permanent socket failure.
Frame specifications
• The carbon-fiber reinforced laminated frame provides an effective
support system with minimal socket coverage.
• The frame is composed of four unified segments: cup area, medial
strut, anterior-proximal extension, and posterior-proximal
extension.
➢ The cup area supports and stabilizes the distal socket. The cup is
trimmed horizontally at the level where the socket walls approach
the vertical. The trim extends over the valve for socket retention
and good appearance.
➢ Width of the medial strut is determined by the two inch carbon-
fiber tape. The trim extends 1/4 inch beyond each edge of the
tape. The anterior/proximal extension covers Scarpa's femoral
triangle. The proximal border follows the trimline of the socket
and extends to the apex of the rectus femoris channel. From this
point, the trim returns to the medial strut, passing about 3/4
inches below the deepest point of Scarpa's triangle.

35. ➢ Forming the ischiogluteal seat, the posterior/proximal extension
terminates at the posterior/lateral corner. At its midpoint, the
posterior frame measures about two inches from top to bottom.
These specifications provide a guide to position the structural layup.
• The layup recommended is 5-12-5 (carbon fiber-fiberglass-
carbon fiber) for the medial strut and 3-6-3 (same material
make-up) for the anterior and posterior extensions.
• For an exceptionally active or heavy individual, additional one or
two layers of carbon-fiber tape may be added to each side of the
layup.
• Since the anterior/medial corner of the frame in the region of the
adductor longus channel is subjected to the greatest stress, care
should be taken to keep the layup from shifting in this area. The
layup in this area should be stitched in place by hand. One may
add layers of Dacron felt in areas, such as the medial brim, which
may require relief.
Complete saturation of the layup with polyester or acrylic resin is
imperative to avoid delamination and structural weakness. Pierce the
dense layers of carbon fiber with an awl to separate the fibers in
order to form channels for laminate entry.
Once laminated, remove the frame from the positive model and
socket carefully to avoid bending segments that may result in
delamination. Care is especially important in the anterior medial
corner. If removal is difficult, the cast should be broken out.

36. Marlo Anatomical Socket (MAS)
Provides support from the pubic ramus rather
than the ischium features lower trim lines in the
anterior and posterior.
Normal Shape Normal Alignment(NSNA)
• First discribed by Ivan Long.
• The socket more closely approximates the shape of the
musculature of a residual limb when compared to a
quad socket.
• The sides, or medial/lateral measurement is tightened
down to squeeze the residual limb, with most
squeezing taking place on the outside or lateral side.
This helps to control the rotation of the socket by
putting pressure along the fleshy area of the leg that
can handle some side to side pressure.