Below knee prosthetic components.pptx

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: PTB socket Air cushion Socket
Other variation Suspension system: Cuff suspension Supracondylar/Suprapetellar System Thigh Corset Rotator Unit 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.