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2 Biomechanics > Knees > Flashcards

Knees Flashcards

1
Q

Tibiofemoral Joint alignment

A

femur slants obliquely due to angle of inclination
knee forms an angle of 170-175°

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2
Q

Genu valgum

A

> 15°
knee going in

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3
Q

Genu varum

A

> 0°, knees going out

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4
Q

Bursa

A

fluid-filled sac that cushions bones, tendons, and muscles around joint
knee has 14

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5
Q

Lateral joint stability

A

IT band
lateral patellar retinaculum
LCL

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6
Q

Medial joint stability

A

posterior medial capsule
medial patellar retinaculum
MCL

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7
Q

Anterior joint stability

A

lateral patellar retinaculum
patellar ligament
medial patellar retinaculum

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8
Q

Posterior joint stability

A

arcuate popliteal ligament
oblique popliteal ligament

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9
Q

Mensici general

A

crescent shaped fibrocartilage structure
transforms tibial into shallow seats for femoral condyles
deeper 2/3 is avascular
anchored by ant and post horns

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10
Q

Ligaments of menisci

A

Coronary
Tranverse
Meniscofibular
Mensicofemoral
MCL

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11
Q

Coronary ligament

A

attaches external edge of menisci to tibia, relatively loose

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12
Q

Transverse ligament

A

stabilizes menisci to each other

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13
Q

Meniscofibular

A

stabilizes lateral meniscus relative to fibula

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14
Q

Mensicofemoral ligament

A

stabilizes lateral mensicus relative to femur

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15
Q

MCL

A

Attaches medial meniscus on its posteromedial border

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16
Q

Function of Mensici

A

reduce stress across tibiofemoral joint during motion, lubricate articular cartilage, proprioception, guide arthrokinematics

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17
Q

How do menisci reduce stress?

A

increases surface area, triples the area of joint contact
helps to combat the 2.5-3x body weight during walking

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18
Q

Tibiofemoral type of joint

A

condyloid, 2 articular surfaces
3 degrees of freedom*

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19
Q

M/L axis of knee

A

inferior and posterior along circular axis
angle of force vectors changes substantially throughout 90°
Axis of rotation is along Medial/lateral, migrates within femoral condyles. alters MA of flexors and extensors

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20
Q

Extensor moment arms

A

greater towards knee extension, at about 20-25° of flexion

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21
Q

Flexor moment arms

A

Greatest towards midrange, except semimembranosus. About 70-90° of flexion

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22
Q

Vertical axis

A

Little motion in FULL extension
most ER/IR comes from when the knee is flexed to 90°
position is based on tibia ON femur

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23
Q

External rotation in knee

A

Tibial ER on fixed femur OR femur IR on fixed tibia

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24
Q

Open chain tibiofemoral

A

Concave on Convex

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25
Q

Closed pack position of knee

A

full extension
ligaments are tight, making more points of contact

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26
Q

Screw how mechanism

A

Locking knee in full extension requires 10° of knee ER
different axis than IR/ER. it is mechanically linked to flexion/extension and cannot be performed independently

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27
Q

Open chain Screw home

A

tibia ER on femur

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28
Q

Closed chain screw home

A

femur IR on tibia

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29
Q

Factors driving screw home

A

Medial condyle shape of 30° lateral curve
Passive tension of ACL
slight lateral pull from vastus lateralis

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30
Q

How does the knee unlock

A

popliteus
femoral ER/tibia IR, depending on if its open/closed chain

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31
Q

Axial rotation of knee

A

described as a spin. happens between menisci and articular surfaces. Causes deformation and compression of menisci

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32
Q

MCL

A

provides resistance against valgus force
stabilizing when knee extended
stabilizes extremes of ER

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33
Q

LCL

A

MCL has twice the tensile strength, this has the same stiffness level
relatively short
no attachment to meniscus

resists varus force
stabilizes knee extension
stabilizes with IR and ER

34
Q

Curciate ligments

A

intracapsular
poor blood supply
resists ant/post forces
provides priorioceptive feeback

35
Q

MCL, ACL, LCL are slack in

A

flexion

36
Q

MCL, ACL, LCL are taut in

A

extension

37
Q

How might the ACL help during open chain knee extension?

A

as knee extensds and tibia slides on femur, ACL prevents excessive anterior slide. becomes increasingly taught during extension

38
Q

The quadriceps are thought of as ACL antagonists. Why?

A

Quads contraction slides tibia anteriorly, which increases strain on ACL

39
Q

The hamstrings are thought of as PCL antagonists. Why?

A

Hamstrings contraction slides tibia posteriorly, increases strain on PCL

40
Q

Hamstrings are antagonists to

A

PCL

41
Q

Quads are antagonists to

A

ACL

42
Q

PCL action

A

any point during range, some fibers are taut, but MOSTLY during flexion. peak is during 90°-120°

43
Q

MCL injury

A

valgus force applied to knee
getting hit on the outside

44
Q

LCL injury

A

varus force applied to knee
inside of knee

45
Q

MCL is best isolated at

A

30° of flexion

46
Q

LCL is best isolated at

A

20 to 30° flexion

47
Q

ACL injury

A

vulnerable in many positions b/c its oblique
ruptures happen when tensile strength exceeds length
20% of injuries are non contact

48
Q

Non-contact ACL injury

A

strong quad contraction with moderate/no flexion
anterior tibial translation
valgus collapse
excessive IR of knee (femur ER on tibia)
excessive closed chain hyperextension of knee

49
Q

Varus/valgus ACL injuries

A

more of a symptom, not a cause. IR/ER torque are 2x more likely to strain ACL

50
Q

ACL testing

A

anterior drawer
lachman’s

at 90° of flexion, ACL provides 85% of total passive resistance

51
Q

PCL injury

A

often from trauma
falling on a flexed knee, tibia hits ground first
dashboard inury–tibia is driven posteriorly

52
Q

PCL testing

A

post drawer test
at 90° of flexion, PCL does 95% of passive resistance

53
Q

Menisci injuries

A

stress is greatest at posterior horns
menisci try to disperse stress in a circular manner
injury at posterior horn decreases ability to withstand hoop stress. less area to disperse force

54
Q

What percent of ACL injuries involve the meniscus?

A

50%
forceful, axial rotation of femoral condyles over a flexed weightbearing knee
torsion pinches and dislodges menisci.

55
Q

Which meniscus is more commonly injured?

A

medial
valgus force increases force and strain on MCL

56
Q

Knee flexors

A

hamstrings

57
Q

Knee extensors

A

quads

58
Q

Knee IR

A

popliteus, semimembranosus, semitendinosus

59
Q

Knee ER

A

biceps femoris

60
Q

Torque of extensors

A

greatest torque generated concides with maximal leverage

61
Q

Which knee extensor has the largest cross sectional area?

A

vastus lateralis
the quads can produce 6-9x weight

62
Q

Q angle

A

between 2 lines
line of pull of quds
line of patella tendon
about 13-15°

63
Q

Torque of flexors

A

greatest torque does NOT coincide with maximal leverage

64
Q

Soleus muscle

A

closed chain pulls tibia posteriorly
can assist hamstrings in stopping anterior tibial displacement, helping ACL

65
Q

Gluteus maximus

A

closed chain: pulls femur posteriorly. Results in anterior position of tibia, not acl protective

66
Q

Patellofemoral Frontal translation plane

A

Medial/lateral shift

67
Q

Patellofemoral Frontal rotation plane

A

medial/lateral rotation

68
Q

Patellofemoral Transverse plane

A

medial/lateral tilt

69
Q

Patella flexion

A

during knee flexion, the patella tracks inferiorly

70
Q

Patellar Extension

A

during knee extension, the patella tracks superior

71
Q

Tibia on femur w/patella

A

patella slides relative to a fixed femur

72
Q

Femur on tibia w/patella

A

femur slides relative to fixed patella

73
Q

Greatest area of contact for patella

A

90-60° of flexion
only 1/3 of the surface is actually contacting
decreasing flexion = patella moving inferiorly

74
Q

Patella function

A

increases the moment arm of the quads, causing an increase in the torque of the quads

75
Q

Patellar tracking

A

malalignment
maltracking

general concept is impacting the area impacts stress; decreased area = increased stress

76
Q

Lateral forces on patella

A

quds, lateral retinaculum, IT band

77
Q

Medial forces on patella

A

vastus medialis, medial retinacular fibers, lateral facet of trochlear groove

78
Q

Vastus medialis and patellar pain

A

increasing strength of VM does NOT lead to decreased pain

79
Q

Medial collapse of patellofemoral joint

A

can be due to natural alignment of genu valgum or poor neuromuscular control
greater femoral adduction and greater femoral internal rotation cause a lateral pull on patella, joint collapses medially

bigger adduction and IR power leads to patellar pain

80
Q

T/F Research suggests that applying an external rotation torque to the tibia produces a greater stress on the ACL compared to an equal but oppositely directed internal rotation torque.

A

False

81
Q

T/F Increasing the hip adduction angle can increase the stress on the patella.

A

True

2 Biomechanics (9 decks)

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