Prosthetic Components and Biomechanics

Question 1

Aspects of patellar tendon-bearing socket

Answer 1

• loads patellar tendon and medial tibial flare
• off-loads tender boney areas
• low posterior trim line to allow for hamstring tendons
• relief for fibular head

Question 2

Aspects of total surface-bearing socket?

Answer 2

• distributes weight bearing over entire surface of residual limb
• goal is uniform pressure and reducing shear forces
• difficult to make correctly

Question 3

Aspects of quadrilateral socket?

Answer 3

• 4 walls that contain the thigh
• flat posterior shelf that is primary weight bearing surface for ischial tuberosity and glute muscles
• Anterior wall higher than posterior

Question 4

Aspects of ischial containment socket

Answer 4

• covers the ischial tuberosity
• wider anterior > posterior than medial > lateral to resist extra femoral abduction
• high medial and posterior wall

Question 5

Pros and Cons of lanyard suspension

Answer 5

Pros

• very secure
• consistent alignment
• does not take much space at bottom of socket

Cons
- visible from outside of socket

Question 6

Pros and Cons of pin-lock suspension

Answer 6

Pros

• very secure
• mechanical connection

Cons

• can cause suction effect
• difficult to align if deaf or blind
• shuttle lock takes up space in socket

Question 7

Pros and Cons of suction suspension

Answer 7

Pros

• good for blood flow
• very good suspension
• provides for fluctuating limb volume

Cons
- can wear out liners quickly

Question 8

Pros and Cons of elevated vacuum suspension

Answer 8

Pros

• very comfortable for the user
• allows for limb volume fluctuations

Cons

• heavy
• must be charged
• extra component that takes up space at the end of the socket

Question 9

What liner is typically used with pin-lock systems, soft and resistant to pressure, durable and good for everyday use?

Answer 9

silicone

Question 10

What liners are good at absorbing pressures, used with vacuum and suction suspension systems?

Answer 10

polyurethane

Question 11

What liners are good for low activity level and for total surface bearing sockets?

Answer 11

copolymer

Question 12

When is the limb the largest in volume?

Answer 12

when the patient first wakes up in the morning

Question 13

What type of foot is typically used with each K level?

Answer 13

K1 - SACH foot (rigid)
K2 - single axis or multi-axial
K3 - Multi-axial
K4 - hydraulic ankle, multiaxial, or crossover

Question 14

Soft vs hard heal of SACH foot

Answer 14

soft - mimic PF and absorb impact more

hard - won’t absorb impact and makes the patient feel like they are in a neutral or DF state

Question 15

What motions are permitted with a single axis foot?

Answer 15

Plantarflexion and dorsiflexion

Question 16

What motions are permitted with multiaxial feet?

Answer 16

plantarflexion and dorsiflexion

inversion and eversion

Question 17

What are the 2 goals of prosthetic knees?

Answer 17

• stance phase control

- swing phase control

Question 18

What knee provides stance control through alignment, encouraging the ground reaction force to be _________ to the knee?

Answer 18

single axis and polycentric knee

- anterior force to the knee

Question 19

What knee is the most stable stance control? How do the patients walk?

Answer 19

• manual locking knee

- patients will circumduct, vault, and hip hike to walk because limb is locked in extension while walking

Question 20

What knee provides for swing phase control by dynamically adjusting swing speed to user’s gait speed? How does it control swing speed?

Answer 20

hydraulic and pneumatic knees

swing speed controlled through friction

Question 21

What knee provides stance and swing phase control? How does it do that?

Answer 21

microprocessor knees

sensors measure joint angles, cadence, etc. to provide stable knee that is responsive

Question 22

What are the pressure tolerant areas in patellar tendon bearing sockets/

Answer 22

• patellar tendon
• pretibials
• posterior distal aspect of residuum
• popliteal fossa, lateral shaft of fibula and tibial flares

Question 23

What rule should you always remember for biomechanics with prosthetics?

Answer 23

head, arms, and trunk will follow where your leg goes

- proximal part of the socket goes in the direction of the head, arms, and trunk

Question 24

Where does the mechanical axis run through in the lower limb? What moment is created at the knee?

Answer 24

• runs from center of femoral head to center of ankle - should cross the knee center
• creates varus moment at the knee

Question 25

Where does the anatomical axis run through in the lower limb? What moment is created at the knee?

Answer 25

• runs through center of femoral shaft and then through tibia
• creates a valgus angle of the knee

Question 26

Where should the foot be in transtibial during bench alignment? What moment does this create at the knee?

Answer 26

0. 5 inch medial to center (medial/lateral stabilization)

- creates varus at the knee

Question 27

Why do you want to avoid a valgus stress at the knee?

Answer 27

a valgus moment at the knee puts pressure in the fibular head which has the peroneal nerve behind it

Question 28

Proximal part of the socket puts pressure on the ______ side of the knee and distal pressure on the _______ side of the residual limb

Answer 28

Proximal - medial

distal - lateral

Question 29

A foot that is too far inset is the same as a socket that is what? What is this also called in reference to the socket?

Answer 29

too far outset

- AKA abducted socket

Question 30

For anterior/posterior stabilization, where should the socket be placed to enhance PTB?

Answer 30

5 degrees of flexion - allows weight bearing through the patellar tendon

Question 31

For anterior/posterior stabilization, where should the foot be placed? Why?

Answer 31

foot slightly posterior to center of socket

- puts the knee in a little bit of a flexor moment so you have more power b/c the quads are on slack

Question 32

Where are the pressures if the foot is too far anterior in transtibial?

Answer 32

anterioproximal and posteriordistal pressure

Question 33

Where are the pressures if the foot is too far posterior in transtibial?

Answer 33

hyperflexion at the knee with posterioproximal and anteriodistal pressures

Question 34

What things are done to minimize rotation of the socket in transfemoral sockets?

Answer 34

• maintain pelvis in posterior tilt on posterior rim
• incorporate ischial/gluteal weightbearing
• adductor longus tendon housed in a groove to prevent breakdown and help block rotation

Question 35

For transfemoral sockets and medial/lateral stability, you want points of force in __________ direction and ________ direction to prevent lateral shifting in socket

Answer 35

proximomedial and distolateral

Question 36

For transfemoral sockets and medial/lateral stability, you want center of heel __________ to ischial tuberosity to promote slight ______

Answer 36

• under or slightly lateral

- promote valgus

Question 37

In transfemoral, foot too far medial: excessive pressure in groin and ________

Answer 37

distolateral

Question 38

In transfemoral, foot too far lateral: excessive pressure proximolateral and _________

Answer 38

distomedial

Question 39

Floor reaction force must stay _______ to the knee joint. Why?

Answer 39

• anterior

- posterior pull will cause flexor moment at the knee leading to instability

Question 40

How much flexion is built into the socket of transfemoral? Why?

Answer 40

• 5 degrees of flexion
• enhances firing of the gluteals to allow hip extension and passively extend the knee
• allows ability to extend the knee w/o lordosis to throw the hip forward and lock the knee out