BELOW KNEE PROSTHESIS AND COMPONENTS

Reported By:

DELA, Angelica Joy A.

MAGALING, Julius

ANATOMY OF THE FOOT & ANKLE

The human foot combines mechanical complexity and structural strength. The ankle serves as foundation, shock absorber, and propulsion engine. The foot can sustain enormous pressure (several tons over the course of a one-mile run) and provides flexibility and resiliency.

The foot and ankle contain: 26 bones (One-quarter of the bones in the human body

are in the feet.); 33 joints; more than 100 muscles, tendons (fibrous tissues that

connect muscles to bones), and ligaments (fibrous tissues that connect bones to other bones); and

a network of blood vessels, nerves, skin, and soft tissue.

- These components work together to provide the body with support, balance, and mobility. A structural flaw or malfunction in any one part can result in the development of problems elsewhere in the body. Abnormalities in other parts of the body can lead to problems in the feet.

Articulation

The lateral malleolus of the fibula and the medial malleolus of the tibia along with the inferior surface of the distal tibia articulate with three facets of the talus. These surfaces are covered by cartilage.

The anterior talus is wider than the posterior talus. When the foot is dorsiflexed , the wider part of the superior talus moves into the articulating surfaces of the tibia and fibula, creating a more stable joint than when the foot is plantar flexed.

Ligaments The ankle joint is bound by the strong deltoid ligament and

three lateral ligaments: the anterior talofibular ligament, the posterior talofibular ligament, and the calcaneofibular ligament.

The deltoid ligament supports the medial side of the joint, and is attached at the medial malleolus of the tibia and connect in four places to the sustentaculum tali of the calcaneus, calcaneonavicular ligament, the navicular tuberosity, and to the medial surface of the talus.

The anterior and posterior talofibular ligaments support the lateral side of the joint from the lateral malleolus of the fibula to the dorsal and ventral ends of the talus.

The calcaneofibular ligament is attached at the lateral malleolus and to the lateral surface of the calcaneus.

The joint is most stable in dorsiflexion and a sprained ankle is more likely to occur when the foot is plantar flexed. This type of injury more frequently occurs at the anterior talofibular ligament.

ANKLE PROSTHESIS Since 1969 at the ankle joint prostheses

are used. Numerous difficulties have ankle prosthetics long time not to be, which hip and knee prostheses in orthopedics show.

The fusion (arthrodesis) at the upper ankle joint is now increasingly seen as a last retreat used for many years because it is known that after stiffening of joints with a big game consequential movement there. The neighboring joints develop regularly called Begleitarthrosen. The prosthesis design and the method of anchoring ankle prosthesis were changed and thus the result of improved therapy.

FOOT-ANKLE ASSEMBLY

Prosthesis terminate in a foot-ankle assembly which substitutes foot and ankle and satisfies basic requirements;

1. Provide a base of weight bearing 2. Absorbs shock at HC and rapidly reach

FF position3. Provide metatarsophalangeal

hyperextension late in stance phase4. Resemble the general contour of the

missing foot

Non-Articulated Components

The foot is attached directly to the shank with neither a joint nor a movement in the region corresponding to the natural ankle.

Popular to its appearanceDurabilityQuieter and lighter than the articulated

components

Symes foot

Used in symes prosthesis The heel wedge is thinner than the

standard sach and the keel is larger for stability and durability

Sculptured toe sach foot

Has more natural appearance than standard sach foot and may be describe if the amputee wares a shoe were forefoot is expose

Comes in various sizes

Postoperative flat heelded foot

Originally designed for ambulation without shoes flowing an immediate postoperative fitting of a prosthesis

Permits equal leg length in standing and walking with or without foot or with flat healed shoes

The wiAde heel and and extra wide toe good for lateral stability

Foot weights 20 % less than in regular molded foot

Used for swimming and water skiing lso used with flat heeled shoes

Veterans administration kingsley

A swim prosthesis that can be fabricated for BKA And AKA by using the Otto back plastic set up

In BKA a PVC Tubing connects the socket in the tube

The shank is made of foam and the prosthesis is laminated

The VAPC is used since 1978 this constricted by Polly propylene is water proof and will not concede in salt water

Can be attached to the ankle Locks 90 degrees for walking 120 degrees

in the swimming

Otto bock universal movable greisiner foot

Offers lateral movement which absorb unevenness to the ground

separate plantarflexion bumpers allow adjustment to resistance

Foot is made of light wood with a flexible shock absorbent sole toe and heal made of padin]

This foot can be used in below knee and above knee amputees

It is more cosmetic lighter than the cable ankle

SACH footFrequently prescribedConsist of a wooden keel covered by

relatively incompressible foam, and a synthetic rubber wedge.

Belts prevents puncturing the soleBolt through the keel attaches the foot to the

shank.It accommodates to an irregular terrain

SACH foot with an external keel

Alternative to SACH footKeel is wider than the basic SACH footHas > mediolateral stabilityImproved appearance than the SACH footMediolateral and transverse motion is

minimized by this design

SAFE foot Aka Stationary Attachment/Flexible

Endoskeleton foot Consist of the rigid bolt block (stationary

attachment) embedded on a flexible keel (the endoskeleton)

Like SACH, it includes a cushion heel for shock absorption and simulated plantarflexion

Permits mediolateral and transverse motion not only by compression of resilient foam but also through keel’s flexibility.

Safe foot is available in any adult sizes, heavier and more expensive than SACH feet in comparable sizes. It can be used for all amputation levels including Syme’s.

STEN foot

Aka Stored energy foot Includes a wood keel which is in three

pieces joined by two rubber plugsTransfer of body weight over the foot first

compresses the plugs then permit it to recoil.

Amount of energy return is quiet modestIt duplicates SACH but it is heavier and

more expensive

SEATTLE foot Earliest energy storing device available was

seattle foot whose derlin keel is C shape with the lower arm elongated as cantilever.

Body weight transfer over the foot bends the cantilevered arm

It returns during late stance contributing to forward propulsion during walking and running

5° of keel flexibility are available Somewhat heavy but provide excellent fxn and

is made in a range of adult sizes Alternate version of reduce weight and

springiness is the SEATTLE LITE FOOT

Carbon Copy IIKeel is composed of two strong but light

plates constructed of carbon composites Longer deflection plate which terminates in

the IP jts. returns energy during walking while the shorter, upper plate is activated under very high loads produces jumping or running.

It lightweight and durable but provides little mediolateral motion

Manufactured in adult sizes to suit shoes of two low-heel heights.

QUANTUM Its keel is the form of spring module consisting of a lower

and upper deflection plate attached to the ankle base. From the base, plates project forward to the MTP jts. and

backward into the heel. Cushion heel is not included in this design Simulated plantarflexion and impact absorption are

provided by the heel deflection plates. Lower two plates is the primary spring that stores and

returns energy during last half of the stance phase, while 2° upper plate act as overload spring in case of unusual high forces.

Spring module or keel is available in several degrees of firmness, encased in a semi flexible cosmetic shell yields medial and lateral permits inversion and eversion.

Manufactured in adult sizes to fit low heeled shoes

Flex-Walk Keel is made of a lightweight carbon graphite

composite Same as the quantum foot, keel extends forward

on the MTP jts. Heel section comes in two versions high- or low

heeled shoe. Broad keels provide little inversion and eversion 9 flex-walk modules of different resistances are

available with choice base on the body weight and activity of the user.

Module is encased in a plastic foam cosmetic cover to create a pleasing appearance

Sizes are available for adults and children

Flex foot The above description of the flex-walk applies equally to

the distal portion of te flex-foot. Flex-foot keel extends from MTP line to the bottom of the

below knee socket or for above knee wearers to the knee unit.

It forms the shank of the prosthesis, acts as long leaf spring bending when loaded and then straightening forcibly when the load is reduced.

It stores and returns energy than any other foot-ankle assembly.

Prosthesis is lighter than one with other foot-ankle components

But it requires sufficient space between the floor and the residuum end and more expensive than other feet.

ARTICULATED COMPONENTS

An assembly in which motion between foot and shank can occur around the articulation in the region corresponding to the anatomical ankle.

More adjustable than the non-articulatedBut heavier and more likely to developed

looseness in the mechanism which can cause unwanted noise.

Single axis assembly

Base of the foot is connected to the ankle block by bolt.

Transverse ankle axis permits the foot to go into plantarflexion and dorsiflexion; all motions is around one axis.

Posterior bumper when compressed resist motion.

Bumper permits 15° of plantar flexion In the opposite direction, motion is resisted by

dorsiflexion stop, it is made of firm rubber, felt or resilient plastic and permits 5° of dorsiflexion.

Multiple- Axis Foot-Ankle Assembly

This assembly permits in any direction; plantarflexion,dorsiflexion, inversion, eversion and a slight amount of rotation around the vertical axis.

Commonly used type of construction Accomodates uneven walking surfaces and

absorbs some of the torsional forces created in walking, reducing torque to the limb by the socket.

But it is bulky, heavy, expensive and may require more maintenance.

Greater latitude of movement may create instability in pts who have marginal coordination.

SHANKMay be exoskeletal (crustacean) or of

endoskeletal (central support or pylon) construction.

Maintains spatial relationship between the socket and the foot, transmit the load from the socket above to the foot below.

Exoskeletal shank is commonly made from light but strong rigid plastic foam,alternately wood maybe used, in which case the space bet. The bottom of the socket and the ankle block should be hollowed to reduce weight.

Endoskeletal type, a metal or plastic tube connects the socket and foot- ankle assembly. It has modest reduction in weight.

But less durable compare to the laminate finished.

SOCKET

Apply weight supporting forces to the amputated limb and transmit forces from the encapsulated residuum to move and control the prosthesis.

PTB Socket Is made of laminated or molded plastic and

provides an intimate fit over the entire area or stump.

It is shaped so that a substantial amount of weight is borne on the patellar tendon, the flares of tibia, and anteriorly on either side of the tibial crest.

Intimately fitted socket should be totally in contact with the entire residuum, including the distal end.

This feature helps to prevent edema, provides additional support area and provides better sensory feedback because of greater are of contact.

Basic PTB socket incorporates a compressible liner or soft insert, commonly formed of Pe-Lite, a closed cell, polyethylene foam.

Hard Socket

Variant of basic PTB socketSoft insert is eliminatedUsed for those with mature residua with

good tissue covering, and for those with severe perspiration problems.

Less likely to be be used for elderly soft is more preferred.

The ISNY PTB socket

All sockets for the lower limb amputee serve two essential purposes; containment of the tissues of the stump and transmission of the body weight to the floor.

ISNY (Icelandic Swedish- New York University) A socket system for below knee amputee

consists of thin, flexible, vacuum formed, thermoplastic PTB socket for tissue containment; and rigid, carbon-fiber-reinforced, laminated frame for weight transmission.

Frame consist of 3 struts (1 posterior and 2 anterior) which connect the distal end cup to the proximal segments covering the patellar tendon, medial flare and ppliteal areas.

Advantages over rigid, plastic laminated socket;1.Enhaced comfort, because the socket’s flexibility allows it to

change shape to correspond with stump changes due to ms. contraction or motion;

2. Thinness (1/16-3/32 inch.) permits improved heat dissipation so that sockets feel cooler;

3. Translucency of the thermoplastic enables it to serve as both a check or trial socket as well as a definitive or permanent socket;

4. Ease and speed of socket modification and replacement are significantly increased.

On the negative side it is less durable and the appearance of the socket- frame combination may be displeasing to some individuals.

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