Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Ortho Implant technology > Unit 3: Knee joint replacemen > Flashcards

Unit 3: Knee joint replacemen Flashcards

1
Q

What design is successfully used in knee replacement?

A

total condylar

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Is the knee joint inherently stable? What provides this?

A

no

- soft tissues provide stability eg ligaments, posterior joint capsule, musculature

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is the posterior joint capsule?

A

a tendinous band that resists hyperextension

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What does subluxation of a joint mean?

A

partial or complete dislocation of the joint

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What type of knee subluxation does the anterior cruciate ligament prevent?

A

posterior

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What type of knee subluxation does the posterior cruciate ligament prevent?

A

anterior

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Which ligament resists knee joint adduction?

A

lateral collateral

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Which ligament resists knee joint abduction?

A

medial collateral

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What quality do ligaments have as they move ?

A

isometric = keep same length

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

How does the position of the instantaneous centre of rotation change as the knee moves from extension to flexion?

A

It moves posteriorly by upwards of 10 mm and distally by a few mm.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Why does the femur not roll off the tibia as the knee flexes?

A

Because the cruciate ligament and joint capsule prevents it from doing so.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is full knee flexion?

A

140

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What movements does the femur do on tibia?

A

sliding due to rotation

rolling motion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

If a prosthetic has a flat tibial plateau and circular condyles. What else does it need? Why?

A

retain cruciates during surgery

to control sliding of femur on tibia

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What type of loading mainly occurs at knee?

A

compressive

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Explain why the joint reaction force at the knee increases as the sideways horizontal component of the ground reaction force increases.

A

As this force increases, a greater patella tendon force and a greater hamstring force are required to balance its effects which adds to the joint reaction force.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What adverse effect could a high contact force in the medial compartment of the knee have on a joint replacement?

A

It will cause high local stresses medially which could cause the underlying cancellous bone to fail.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What components does the joint reaction force at the knee have?

A

vertical
fore-aft
horizontal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What does the medial horizontal component of the joint reaction force generate at the knee?

A

a turning moment

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

List the three important functional kinematic requirements of a replacement knee.

A

fully extend to 180
flex to 90
slight axial rotation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

During knee replacement surgery, what must be done to

(i) the posterior capsule
(ii) the collateral ligaments?
iii) bearing surfaces?

A

i) dissected out so knee can extend
ii) tension balanced
iii) cut parallel

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Is the cost of knee more or less than hip?

A

5x more than hip

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is the femoral and tibial component usually made of/

A 
femoral = cobalt chrome
tibial = HDP
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What does constraint mean?

A

the relationship between tibial and femoral bearing surface geometries.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

If there are no intact ligaments, which design of prosthesis should be used?

A

hinged

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Describe movement with a hinged prosthesis

A

single axis of rotation

no give under lateral and long axis rotational loading

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What disadvantage does a hinged prosthesis have?

A

transmits high shear forces at the interface

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

Which ligaments are usually intact before a knee replacement?

A

collaterals fine and can be balanced

ACL destroyed by OA

PCL usually there

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What motion

is the PCL important for?

A

controlling rolling motion of tibia

allows femur to rotate allowing flexion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

If the PCL is not preserved, what must be done?

A

substitute within the prosthesis with a simple stop or cam-like device

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

What are the advantages of retaining the PCL?

A
  • AP stability
  • proprioception
  • walking on stairs
  • better ROM
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

What are the disadvantages of retaining the PCL?

A
  • constricts removing the posterior capsule so full extension can be limited
  • femoral component sliding over tibial bearing may increase wear
  • means a congruent joint surface isnt used that limits HDP wear
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

What features are needed if the PCL is retained?

A

flat tibial plateau
correct PCL tension
sloped tibial component 10degrees posterior

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

What negative effect can prosthesis designs that retain the PCL have?

A

HDP wear and fatigue problems

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

Why does a replacement knee need to have a fairly flat tibial plateau when the PCL is retained?

A

Because the PCL could otherwise become lax or too tight during flexion- extension movement.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

Which mechanical factor affects load transmission?

A

degree of constraint

37
Q

Which mechanical factor affects the wear of the HDP tibial component?

A

surface contact

38
Q

Which mechanical factor affects stresses in the HDP tibial component?

A

surface contact area

39
Q

How does constraint affect load transmission?

A

a rigid joint cannot transmit any load via the soft tissues so it all transfers through the prosthesis-bone interface

40
Q

What type of constraint exists in most replacements?

A

axial rotation

lateral motion

41
Q

Which type of knee replacement is the most constrained?

A

hinge

42
Q

How are cement and prosthesis materials affected by constrained load transmission?

A

they are stiff and not viscoelastic so sudden loads cause large instantaneous stresses at the interface that can cause failure

43
Q

What helps constrained load transmission?

A

large contact area using stems and pegs in the components

44
Q

What determines the useful life of the prosthesis?

A

the rate of wear of the HDP component

45
Q

What is the volume of wear of a knee prosthesis proportional to?

A

sliding distance moved

46
Q

What formula shows the volume of wear in a knee prosthesis? why?

A

v = K.s

because c, N and p were constants

47
Q

What effect does diameter of bearing have on volume of wear material produced?

A

a smaller diameter reduces volume of wear

48
Q

Why is it better to have a smaller volume of wear?

A

fewer HDP particles

49
Q

How does volume of wear relate to depth of wear?

A

volume of wear = area of contact x depth of wear

v = A x t

50
Q

How can depth of wear be reduced?

A

having a large surface area of contact

51
Q

Why is it advantageous to increase the width instead of the diameter of bearing?

A

increasing diameter increases volume of wear

52
Q

Why does HDP fatigue occur?

A

high contact stresses

cyclical sliding motion between surfaces

53
Q

What does HDP fatigue cause?

A

premature wear and subsurface lamination cracking

54
Q

What is the contact stress dependent on?

A

increased contact area, due to shape of bearing, will decreases contact stresses

55
Q

Why is a curved femoral condyle better for contact stresses?

A

moment due to lateral ground reaction force lifts condyle up and all load goes through the other

a curved condyle has more contact area for the stress to pass through

56
Q

How does the contact area for the tibial component vary?

A

from flexion to extension

57
Q

Which part of the contact area is in

a) compression?
b) tension?

A

a) centre

b) periphery

58
Q

Why is the HDP tibial component prone to fatigue failure?

A

contact points change between flexion and extension

it experiences repetitive loading / unloading and tensile / compressive loading cycles.

59
Q

List four design features of a tibial component that affect the magnitude of the stresses on the underlying bone.

A

Thickness of HDP component
If there is a metal backing plate
If there is a tibial stem(peg)
Stiffness of HDP component

60
Q

How does thickness of HDP component affect contact stresses? why?

A

thin HDP has greater stresses because they can’t be evenly distributed

61
Q

How is load distributed on the tibial plateau?

A

medial side is 60% of load

62
Q

State one advantage of a modular tibial component that can take different thicknesses of tibial insert.

A

allows for ligaments to be balanced

63
Q

What is the advantage of using a metal backing plate?

A

even distribution of high contact stresses on tibial plateau

64
Q

What is a disadvantage of using a metal backing plate?

A

it may cause excessively high stresses on the medial bone if the knee is unevenly loaded because the metal plate is stiff and therefore does not spread out a high contact load as the less stiff HDP.

65
Q

What advantage does a tibial stem have? How?

A

prevents sinkage and loosening by reducing high contact stresses as it resists medial vertical load with a lateral reaction force

66
Q

How has design of knee prosthesis improved since total condylar?

A

posterior stabilised models have a design that takes over the job of PCL so it doesn’t need to be retained

67
Q

How are the femoral condyles different in a prosthesis than in a normal knee?

A

normal = asymmetrical with large medial aiding axial rotation in full extension

prosthesis = symmetrical condyles for ease and cost

68
Q

Which movement has a smaller radius of curvature: flexion or extension?

A

flexion

69
Q

What is the role of the anterior part of the femoral component curvature?

A

accommodates movement of the patella during flexion and extension

70
Q

Which component is most important for the degree of constraint?

A

tibial

71
Q

Describe a posterior stabilised prosthesis

A

dished surface
prevents posterior subluxation of femur on tibia
allows femur to roll back as it flexes

uses a stop or cam device

72
Q

Which method of posterior stabilisation is better? why?

A

cam device because the curved shape allows for a more smooth, roll-back in flexion

73
Q

What features of a knee prosthesis provide rotational stability?

A

Projections on the undersurface of the tibial or femoral components, the stem (if present), screws (if present).

74
Q

What additional fixation methods are required for cementless knee prostheses?

A

Screws and/or stem, to provide the required fixation.

75
Q

How does the absence of a patella affect the knee extension force applied in the quadriceps?

A

The patella tendon lever arm is reduced, requiring a greater quadriceps force. This adds to the patello-femoral joint reaction force.

76
Q

Why is a metal backed patella replacement generally undesirable?

A

The HDP is too thin to prevent high stresses in the material, which can result in extremely fast wear.

77
Q

What can be done to encourage patellar tracking?

A

groove anterior femoral component

78
Q

What 2 things can reduce wear of patellar bearing?

A

contour to femur

dont use metal backing

79
Q

In which type of arthritis, is the patellar bearing surface always replaced?

A

rheumatoid

80
Q

What is the advantage of using meniscal bearing knee prostheses.

A

lowers contact stresses.

81
Q

What is the disadvantage of using meniscal bearing knee prostheses.

A

requires removal of more bone,

more difficult operation to perform.

82
Q

Where does the meniscus move during

a) flexion?
b) extension?

A

a) back

b) forward

83
Q

How can the risk of dislocation with a meniscal bearing prosthesis be reduced?

A

limit sliding

84
Q

What is a hemi-arthroplasty?

A

when one side of the tibio-femoral joint is replaced

85
Q

Who benefits from hemi-arthroplasty?

A

younger patient
severe pain and deformity
in-between osteotomy and TKR

86
Q

Why are two pegs commonly used on unicompartmental surface replacement?

A

To resist the tendency to rotate under torsional loading.

87
Q

Give two problems with revision knees

A

loss of bone stock

need for alignment and stability

88
Q

What is the function of an augmentation block?

A

To fill in gaps between the prosthesis and the bone. This is frequently required during revision procedures, where some bone will be lost as a result of the primary arthroplasty or because it is no longer viable.

89
Q

If an augmentation block cant account for all the bone loss what can be used instead?

A

intramedullary stem in femur and tibia

Ortho Implant technology (7 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions