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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
Closed pack position of knee
full extension ligaments are tight, making more points of contact
26
Screw how mechanism
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
27
Open chain Screw home
tibia ER on femur
28
Closed chain screw home
femur IR on tibia
29
Factors driving screw home
Medial condyle shape of 30° lateral curve Passive tension of ACL slight lateral pull from vastus lateralis
30
How does the knee unlock
popliteus femoral ER/tibia IR, depending on if its open/closed chain
31
Axial rotation of knee
described as a spin. happens between menisci and articular surfaces. Causes deformation and compression of menisci
32
MCL
provides resistance against valgus force stabilizing when knee extended stabilizes extremes of ER
33
LCL
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
Curciate ligments
intracapsular poor blood supply resists ant/post forces provides priorioceptive feeback
35
MCL, ACL, LCL are slack in
flexion
36
MCL, ACL, LCL are taut in
extension
37
How might the ACL help during open chain knee extension?
as knee extensds and tibia slides on femur, ACL prevents excessive anterior slide. becomes increasingly taught during extension
38
The quadriceps are thought of as ACL antagonists. Why?
Quads contraction slides tibia anteriorly, which increases strain on ACL
39
The hamstrings are thought of as PCL antagonists. Why?
Hamstrings contraction slides tibia posteriorly, increases strain on PCL
40
Hamstrings are antagonists to
PCL
41
Quads are antagonists to
ACL
42
PCL action
any point during range, some fibers are taut, but MOSTLY during flexion. peak is during 90°-120°
43
MCL injury
valgus force applied to knee getting hit on the outside
44
LCL injury
varus force applied to knee inside of knee
45
MCL is best isolated at
30° of flexion
46
LCL is best isolated at
20 to 30° flexion
47
ACL injury
vulnerable in many positions b/c its oblique ruptures happen when tensile strength exceeds length 20% of injuries are non contact
48
Non-contact ACL injury
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
Varus/valgus ACL injuries
more of a symptom, not a cause. IR/ER torque are 2x more likely to strain ACL
50
ACL testing
anterior drawer lachman's at 90° of flexion, ACL provides 85% of total passive resistance
51
PCL injury
often from trauma falling on a flexed knee, tibia hits ground first dashboard inury--tibia is driven posteriorly
52
PCL testing
post drawer test at 90° of flexion, PCL does 95% of passive resistance
53
Menisci injuries
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
What percent of ACL injuries involve the meniscus?
50% forceful, axial rotation of femoral condyles over a flexed weightbearing knee torsion pinches and dislodges menisci.
55
Which meniscus is more commonly injured?
medial valgus force increases force and strain on MCL
56
Knee flexors
hamstrings
57
Knee extensors
quads
58
Knee IR
popliteus, semimembranosus, semitendinosus
59
Knee ER
biceps femoris
60
Torque of extensors
greatest torque generated concides with maximal leverage
61
Which knee extensor has the largest cross sectional area?
vastus lateralis the quads can produce 6-9x weight
62
Q angle
between 2 lines line of pull of quds line of patella tendon about 13-15°
63
Torque of flexors
greatest torque does NOT coincide with maximal leverage
64
Soleus muscle
closed chain pulls tibia posteriorly can assist hamstrings in stopping anterior tibial displacement, helping ACL
65
Gluteus maximus
closed chain: pulls femur posteriorly. Results in anterior position of tibia, not acl protective
66
Patellofemoral Frontal translation plane
Medial/lateral shift
67
Patellofemoral Frontal rotation plane
medial/lateral rotation
68
Patellofemoral Transverse plane
medial/lateral tilt
69
Patella flexion
during knee flexion, the patella tracks inferiorly
70
Patellar Extension
during knee extension, the patella tracks superior
71
Tibia on femur w/patella
patella slides relative to a fixed femur
72
Femur on tibia w/patella
femur slides relative to fixed patella
73
Greatest area of contact for patella
90-60° of flexion only 1/3 of the surface is actually contacting decreasing flexion = patella moving inferiorly
74
Patella function
increases the moment arm of the quads, causing an increase in the torque of the quads
75
Patellar tracking
malalignment maltracking general concept is impacting the area impacts stress; decreased area = increased stress
76
Lateral forces on patella
quds, lateral retinaculum, IT band
77
Medial forces on patella
vastus medialis, medial retinacular fibers, lateral facet of trochlear groove
78
Vastus medialis and patellar pain
increasing strength of VM does NOT lead to decreased pain
79
Medial collapse of patellofemoral joint
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
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.
False
81
T/F Increasing the hip adduction angle can increase the stress on the patella.
True

2 Biomechanics (9 decks)

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