The patellar-tendon-bearing socket is made of laminated or molded plastic that provides an intimate fit over the entire area of the amputated portion of the limb, including the distal end. The anterior wall of the socket is high enough to encompass the distal half of the patella while the posterior wall rises slightly higher than the apex of the in- ward bulge of the socket at the level of the patellar tendon. The medial and lateral walls are slightly higher than the anterior wall to control mediolateral forces applied to the stump, thereby enhancing stability, in this plane. The basic PTB socket also incorporates a soft insert liner Provide: The PTB socket provides total contact with the stump. This feature helps to prevent edema, provides some additional support area (although the end of the stump cannot tolerate much pressure), and probably provides better sensory feedback to the wearer because of the greater area of contact between the amputated limb and the socket Air cushion Socket One of the designs, the PTB air-cushion socket, consists of an elastic inner sleeve (stockinette impregnated with silicone rubber) within a rigid outer shell and cap. A sealed chamber between these two walls contains air at atmospheric pressure. Distal support is provided by the tension of the sleeve itself and by compression of the air sealed in the chamber. The advantages of the air-cushion socket are that is offers a possibility for higher distal loading, Maintains distal contact even when limb volume changes slightly, Lessens skin damage due to stretching of skin against an unyielding surface. The increased distal loading may enhance circulation by decreasing the need for more constrictive proximal loading. Two major difficulties are that it is complicated to fabricate and, once completed, modifications are very difficult. Other Socket Variations In addition to the variations-described above, which relate primarily to weight-bearing characteristics. Other variations of the basic PTB socket involve the upward extension of the anterior, medial, and lateral walls to provide al- ternate means of suspension. Since these designs relate to suspension, they are described in the section that follows. Supracondylar Suprapetellar System The basic PTB prosthesis is suspended by means of a supracondylar cuff ,which is attached to the socket in the posteromedial and posterolateral areas, and encircles the thigh just above the femoral epicondyles and patella . The supracondylar cuff serves-primarily to retain the prosthesis on the stump. It provides only slight assistance for mediolateral stability but does resist forces that tend to force the knee into hyperextension. Most amputees, with the possible exception of those with very-short or painful stumps, find the stump-socket pressures well within their tolerance with this type of suspension. The supracondylar/suprapatellar (SC/SP) suspension system has similarly high medial and lateral.

1. Lower limb
prosthetics
Prosthetic Components
Socket:
1. PTB socket
2. Air cushion Socket
3. Other variation
Suspension system:
1. Cuff suspension
2. Supracondylar/Suprapetellar System
3. Thigh Corset
4. Rotator Unit
5. Modular Construction

2. Patellar tendon bearing (PTB) socket:
• The patellar-tendon-bearing socket is made of laminated or molded
plastic that provides an intimate fit over the entire area of the amputated
portion of the limb, including the distal end. The anterior wall of the
socket is high enough to encompass the distal half of the patella while
the posterior wall rises slightly higher than the apex of the in- ward
bulge of the socket at the level of the patellar tendon. The medial and
lateral walls are slightly higher than the anterior wall to control
mediolateral forces applied to the stump, thereby enhancing stability, in
this plane. The basic PTB socket also incorporates a soft insert liner

3. Provide:
The PTB socket provides total contact with the
stump.
This feature helps to prevent edema, provides
some additional support area (although the end
of the stump cannot tolerate much pressure),
and probably provides better sensory feedback
to the wearer because of the greater area of
contact between the amputated limb and the
socket

4. Air cushion Socket:
One of the designs, the PTB air-cushion
socket, consists of an elastic inner sleeve
(stockinette impregnated with silicone rubber)
within a rigid outer shell and cap. A sealed
chamber between these two walls contains air
at atmospheric pressure. Distal support is
provided by the tension of the sleeve itself and
by compression of the air sealed in the
chamber.

5. Advantages & Difficulties
• The advantages of the air-cushion socket are that is offers a
possibility for higher distal loading,
• maintains distal contact even when limb volume changes slightly,
• lessens skin damage due to stretching of skin against an unyielding
surface.
• The increased distal loading may enhance circulation by decreasing
the need for more constrictive proximal loading.
• Two major difficulties are that it is complicated to fabricate and,
once completed, modifications are very difficult.

6. Other Socket Variations
In addition to the variations-described above, which relate primarily to
weight-bearing characteristics.
Other variations of the basic PTB socket involve the upward extension of
the anterior, medial, and lateral walls to provide al- ternate means of
suspension.
Since these designs relate to suspension, they are described in the
section that follows.

7. Suspension Systems
Cuff suspension:
• The basic PTB prosthesis is suspended by means of a
supracondylar cuff ,which is attached to the socket in the
posteromedial and posterolateral areas, and encircles the
thigh just above the femoral epicondyles and patella
• . The supracondylar cuff serves-primarily to retain the
prosthesis on the stump.
• It provides only slight assistance for mediolateral stability but
does resist forces that tend to force the knee into
hyperextension.
• Most amputees, with the possible exception of those with
very-short or painful stumps, find the stump-socket pressures
well within their tolerance with this type of suspension.

8. Supracondylar/Suprapatellar
(SC/SP) System
The supracondylar/suprapatellar (SC/SP)
suspension system has similarly high medial and
lateral walls on the socket as does the
supracondylar system, but uses a removable,
compressible insert to allow the amputated limb to
pass the close-fitting proximal brim. In addition, the
SC/SP has a high anterior wall which covers the
entire patella.

9. • Both of the above suspension variants provide greater mediolateral
stability at the knee and eliminate the cuff. The high molded anterior wall
of the SC/SP not only helps retain the prosthesis-on the limb, but
effectively resists any tendency towards recurvatum.
• These variants are more difficult to fit than the standard PTB. The
proximal brims of both the SC with the medial wedge and the SC/SP are
somewhat more bulky while the SC/SP may restrict flexion, especially in
kneeling.

10. Thigh Corset
The thigh corset is attached to the socket and shank by the side
bars and knee- joint assembly. In addition to holding the prosthesis
on the leg during swing phase, the corset supports part of the body
weight and helps to provide stability in stance phase. In some cases
a flexible waist belt and fork-strap assembly are used to aid in
suspension.
In as much as the human knee joint is not a simple single-axis joint,
some relative motion between the prosthesis and the limb will occur
when single-axis mechanical joints are used. This relative motion
can cause chafing, irritation, and pressures of the stump. Other
disadvantages of the thigh corset are that it is bulky, adds to the
weight of the prosthesis, its constricting effect may cause atrophy of
the thigh, and it may aggravate any edema in the amputated limb.

11. When an amputee walks, the socket tends to twist on the
amputated limb, causing a shearing effect at the stump-socket
interface.
To cope with this problem, a torque- absorber rotator
mechanism has been developed for use with lower-limb
prostheses . It is usually not indicated for below-knee amputees
with basic PTB prostheses with supra- condylar cuff
suspension, but may be useful for a below-knee amputee who
has a thigh corset who is encountering discomfort.
The rotator unit is interposed between the lower end of the
shank and the foot-ankle assembly. A resilient element that is
incorporated between the upper and lower attachments of the
unit permits the rotation of the shank to take place while the foot
is in contact with the floor. Different models are available for use
with exoskeletal and endoskeletal shank construction.
Rotator unit

12. Modular Construction
• The basic concept of modular design of prostheses involves the utilization of
standardized inter- changeable components that can be assembled to provide a
prosthesis that meets the needs of individual amputees. Several modular
systems are available. While there are differences in these systems, there are
also basic Similarities namely:
• 1. Utilization of a tubular structural member that constitutes the internal
skeleton, and to which foot-ankle and knee assemblies, sockets and other
components can be easily attached.
• 2. A covering of soft material over the endoskeletal structure-to provide a lifelike
appearance.

13. Modular Construction cont.
• 3. Incorporation of a means of adjusting the alignment of the prosthesis.
• When the fitting and alignment process has been completed, excess wood that serves to
connect the socket and tubular shank is removed. A soft cosmetic covering is fitted over the
socket and endoskeletal shank and the cosmetic covering is shaped to provide a good
appearance.