Prostheses

The principal lower limb prostheses are• Partial foot prostheses• Syme’s prosthesis• Transtibial prostheses• Transfemoral prostheses• Knee disarticulation• Hip disarticulation

Partial Foot Prostheses

• Purpose1. Restore foot function particularly in walking2. Simulate the shape of the missing foot

segment• Indications1. Loss of one or more toes2. Transmetatarsal amputation3. Amputation or disarticulation through tarsals

Partial Foot Prostheses• Loss of one or more toes Pad the toe section to improve appearance of the upper

section of the shoe Arch support to maintain alignment of amputated foot.• Transmetatarsal amputation Plastic socket to protect amputated ends of the metatarsals Rigid plate restores the foot length Toe filler Rocker bar at the bottom of the prosthesis to aid late stance.

Partial foot prostheses

• Amputation or disarticulation through tarsalsProstheses used in transmetatarsal

amputation augmented with a plastic calf shell which is strapped around the leg.

Trans-tibial Prostheses

Trans-tibial level refers to -• Amputation in which tibia and fibula are

transected• Retention of anatomical knee joint• Intact motor and sensory functions.• Indicated in vascular diseases.

Parts of Trans-tibial Prostheses

1. Foot-ankle assembly2. Socket3. Shank4. Suspension component

Foot-ankle assembly

Uses• Restores contour of the foot• Absorbs shock at heel contact• Plantarflexes in early stance• Simulates metatarsophalangeal

hyperextension in late stance phase• In neutral position during swing phase

Foot-ankle assembly

Types• Non-articulated feet1. SACH foot (solid ankle cushion heel)2. SAFE foot (stationary attachment flexible

endoskeleton)• Articulated feet1. Single-Axis feet2. Multiple-Axis feet

SACH FOOT (Solid ankle Cushion Heel)

SAFE FOOT ( Solid Ankle Flexible Endoskeleton)

Shank

Substitute for human leg Restores length and shape Located above foot-ankle assembly and

below socket in transtibial prostheses Types• Exoskeleton shank• Endoskeleton shank

ENDOSKELETON EXOSKELETON

Socket

Uses• Maximum distribution of load• Assist in venous blood circulation• Provide tactile feedbackPatellar tendon bearing (PTB) socket has a

prominent indentation over patella tendon.Socket has reliefs and build-ups

Structure of Socket

• Reliefs-concavities in the socket over areas contacting sensitive structures such as bony prominences.

• Located over i. fibular head, ii. tibial crest, iii. tibial condyles and iv. anterior-distal tibia.• Posterior brim is trimmed to provide room for

hamstring tendons

Structure of Socket

• Build-ups- convexities n the socket over areas contacting pressure-tolerant tissues.

• Located over i. belly of gastrocnemius,ii. patellar tendon, iii. proximomedial tibia (pes anserinus) and iv. tibial and fibular shafts.

Alignment of Socket

On the shank in slight flexion and in slight lateral tilt.

• Flexion i. enhances loading on patellar tendon,ii. prevent genu recurvatum,iii. resist tendency of amputated limb to slide too

deeply into socket, iv. facilitates contraction of quadriceps muscle• Lateral tilt reduces loading on fibular head

Types of socket• Lined socket i. Made of polyethylene foam liner, silicone ii. Liner adds or reduces volume of the socketiii. Adds to the bulk of the prosthesisiv. Heat insulatorv. Reduces risk of abrasion between socket and skin• Unlined socketi. Made of thermoplastic materialii. Usually given when stump has stabilized in volumeiii. Easier to cleaniv. Difficult to alter the shape of the socket.

Suspension

• Prosthesis requires some from suspension to hold it in place while walking or climbing stairs or jumping.

• Types of suspensioni. Cuff variantsii. Distal attachmentiii. Brim variants iv. Thigh corsetv. Vacuum-assisted socket system

PTB Transtibial prosthesis

PTB SC/SP

Trans-femoral prosthesis

Components• Foot-ankle assembly • Shank• Knee unit• Socket• Suspension device

Knee Unit

Knee units have four features:• Axis• Friction mechanism• Extension aid• Mechanical stabilizer

Knee Unit: AXIS SYSYTEM

Two types of knee unitsi. Single axisii. Polycentric linkagea) 4 or more pivoting barsb) Provide greater stabilityc) center of knee rotation in posterior to

weight bearing line

Knee Unit: FRICTION MECHANISMS

• Change the knee swing by modifying speed of knee motion during swing phase

• Affect knee swing according to walking speed.• Two factors affecting friction mechanism arei. Time during swing phase when friction

affects knee jointii. medium through which mechanism operates

Knee unit:FRICTION MECHANISMS

• Constant frictioni. Clamp grasping knee jointii. Amount of friction is unvarying in swing phaseiii. Manually adjusted to loosen or tighten• Variable frictioni. Amount of friction is variable in swing phaseii. Early swing –high frictioniii. Mid-swing –friction diminishesiv. Late swing -friction increases

Knee Unit: FRICTION MECHANISM

Medium Sliding friction Fluid friction - hydraulic friction - pneumatic friction Microprocessor controls

Knee Unit: EXTENSION AID

• A mechanism to assist knee extension during latter part of swing phase

• Types-i. Elastic webbingii. Internal extension aid

Knee Unit:STABILIZERS

• To increase stability of knee unit• Hip motion controls knee action, aided by

alignment of knee in relation to other components of prosthesis

• Knee joint is aligned posterior to line extending from trochanter to ankle (TKA line)

• Typesi. Manual lockii. Friction brakes

SOCKET

Pressure tolerant areas• Gluteal musculature• Sides of the thigh• And distal end of

amputated limb

Pressure sensitive areas• Pubic symphysis• Perineum

Types of socket

Quadrilateral socket i. Post wall-ischial tuberosity +

gluteal musclesii. Ant wall- applies post directed

pressureiii. Lat wall- aid in medio-lateral

stabilizationiv. Med wallReliefsv. Antero-medialvi. Postero-medialvii. Antero-lateralviii. Postero-lateral

Ischial Containment socketi. Contoured adducted

trochanter-controlled alignment method.

ii. Covers ischial tuberosity and part of ischiopubic ramus to increase stability.

iii. To increase frontal stability medial-lateral width is narrow.

iv. Lateral wall covers greater trochanter.

Suspension Suction suspensioni. Refers to pressure differences inside and outside the socket.ii. In suction suspension,(int socket press) < (ext pressure),

therefore atm press. causes the socket to remain on the thigh

iii. One-way air-release valve enables residual air to be expellediv. Types of suspension are a) total suction,b) partial suction and c) no suction

Suspension in Transfemoral Prosthesis

FIT AND ALIGNMENT

• FITi. Snug fitting to minimize chaffing and

maximize control• ALIGNMENT – slight socket flexioni. Facilitates contraction of hip extensorsii. Reduce lumbar lordosisiii. Allows equal step length

DIFFERENT TYPES OF LOWER LIMB PROSTHESIS

KNEE DISARTICULATION PROSTHESIS

Excellent prosthetic control becausei. Thigh leverage is

maximumii. Body weight can be borne

through distal end of femur

iii. Epicondyles provide rotational stability

HIP DISARTICULATION PROSTHESIS

• Indications i. Amputation above greater trochanter (short

transfemoral)ii. Removal of the femoral head from

acetabulum (hip disarticulation)iii. Removal of femur and portion of pelvis

(transpelvic amputation)

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