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Unit 2 > 10-14b Knee Biomechanics I > Flashcards

10-14b Knee Biomechanics I Flashcards

1
Q

Why is the tibiofemoral joint so commonly injured?

A

Lots of sagittal plane motion (not as much transversal/frontal plane motion)

Lots of force (longest bones in the body = lots of force); if they go in the opposite directions = bad

Above and below: the knee is the symptom to hip, ankle, and foot motion. Caught in between more mobile joints

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2
Q

What are the two articulations of the tibiofemoral joint?

A

medial femoral condyle articulating with the medial tibial plateau

lateral femoral condyle articulating with the lateral tibial plateau

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3
Q

Which condyle on the femur projects more distally?

A

medial condyle by about 2/3 of an inch

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4
Q

Where do the cruciate ligaments attach?

A

intercondylar fossa

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5
Q

What does the patella engage with on the femur during early flexion?

A

trochlear groove

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6
Q

In which plane are the femoral condyles more convex? Frontal or sagittal?

A

Sagittal

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7
Q

How do the tibial condyles project in the frontal plane?

A

slightly concave

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8
Q

How do the tibial condyles project in the sagittal plane?

A

medial: slightly concave
lateral: slightly convex

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9
Q

Which condyle has a longer anterior-posterior length?

A

medial condyle

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10
Q

What attaches at the intercondylar tubercles?

A

cruciate ligaments

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11
Q

What fills the joint space of the tibiofemoral joint?

A

hyaline cartilage

meniscus

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12
Q

How does the medial meniscus compare to the lateral meniscus shape-wise?

A

medial meniscus: C shape

lateral meniscus: circular O shape

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13
Q

How does the meniscus help the articulation of the femur and tibia?

A

gives the femur a concave shape to rest in

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14
Q

What are the primary functions of the menisci?

A

Enhance TF congruency: distribution of forces by increasing the contact area to absorb 40-60% of the normal load: shock absorbers

help with friction/shear reduction

provide joint stability

assist in lubrication of the joint: hyaline cartilage has poor joint supply, so another structure forces more synovial fluid against the hyaline cartilage and provides more nutrients

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15
Q

What are the secondary directions in which the meniscus stabilizes?

A

restrains movement in A/P directions

and with combined valgus and rotation by providing stability

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16
Q

What are the implications of a menisectomy?

A

contact area decreases and adds stress to the femur (Stress = Force/Contact Area)

long-term consequences are arthritis (14 times more likely for OA w/ menisectomy)

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17
Q

Describe Meniscal mobility. Which one is more mobile? How does weight-bearing affect mobility?

A

Medial meniscus is more restricted due to greater ligamentous/capsular restraints (MCL)

Implications: more medial meniscus problems due to lack of mobility

In non-weightbearing: not much difference in mobility (less need for deformity)

In weightbearing: more deformity and sliding

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18
Q

How do the menisci move during knee extension?

A

deform and slide anteriorly

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19
Q

How do the menisci move during knee flexion?

A

deform and slide posteriorly

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20
Q

What muscle(s) help the menisci move during knee flexion?

A

medial meniscus by semimembranosis

lateral meniscus by popliteus

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21
Q

What are the most common mechanisms for meniscal tears? Which meniscus is more likely to tear? What causes a springy end-feel/locked knee?

A

twisting/pivoting on loaded limb
medial meniscus
local synovitis (assoc. with inflammation of synovium)
bucket handle tear: meniscus flipped up inside the joint

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22
Q

What would a yellowish aspiration from menisci mean vs. red aspiration?

A

yellowish fluid: synovitis so not good for surgery b/c cannot heal

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23
Q

Where do the menisci get their nutrition? Where do the different parts receive their nutrients?

A

lateral third gets blood supply up into the pt’s 50s (after fifties only periphery)

peripherally: supplied from capillaries
centrally: relies on diffusion from the synovium (aided by cyclic loading, while immobilization/NWB is problematic

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24
Q

What are the types of articular cartilage injuries?

A

focal lesions (acute): traumatic in origin, focal surface injury, peripheral tissue is normal

degenerative lesions: multiple causes (aging), peripheral tissues affected, OA

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25
What does normal TF alignment consist of?
slight genu valgum 170-175 degrees males > females due to wider pelvis in women (more genu valgum/knock-knee)
26
What are the two abnormal alignments of TF alignment?
genu valgum: knock-knee at <= 165 degrees genu varum: bow-legged at >= 180 degrees
27
In bilateral stance, what are the mechanical axes?
Femur (FM): femoral head to knee center Tibia (TM): knee center to ankle center
28
How does a varus situation affect the LBA? Implications? Torque?
axes are off and LBA comes medial to the knee compression of medial side can cause wearing of the medial joint compartment Varus adduction moment
29
How does a valgus situation affect the LBA? Torque?
LBA comes outside the knee causes valgus abduction moment
30
How much does the articular cartilage deform during weight bearing? Single leg stance?
deforms by 22-30% Single leg stance: Compartment loads: medial bears greatest load at 2.25x BW (lateral: 0.91x BW) natural varus (adduction) torque due to medial-leaning COM; more pronounced varus torque in bow-legged individuals = medial compression
31
How do we reduce adduction moments?
surgically: osteotomy: surgical wedge to correct alignment (for one with very isolated arthritis); TKA and conservatively: wedging in someone's shoe/bracing/gait modification (strengthen quads) to reduce adduction moment
32
What are we referring to with knee osteokinematics? What are the 6 DOF?
Flexion/extension Internal/external rotation Abduction/adduction (valgus/varus) tibial and femoral displacement: med/lat, sup/inf, ant/post.
33
How do we measure adduction (varus) and abduction (valgus)?
relationship of the distal segment relative to the midline of the proximal segment
34
When the tibia moves medial to the femur's midline what kind of moment is it?
varus (adduction) moment
35
When the tibia moves lateral to the femur's midline what kind of moment is it?
valgus (abduction) moment
36
When the femur moves lateral to the tibia
varus (adduction) moment
37
When the femur moves medial to the tibia
valgus (adduction) moment
38
If the femur internally rotates, what kind of rotation happens to the tibia?
external rotation
39
When femur externally rotates, the tibia moves in what direction relative to the femur?
internal rotation
40
How do we describe the relationship of distal and proximal segments in rotation?
rel. distal segment relative to midline of the proximal segment
41
During flexion/extension, where is the axis of motion? | What movements occur?
horizontal line passing through the femoral epicondyles (axis) flexion: posterior roll and anterior glide of femur on tibia extension: anterior roll and posterior glide
42
as we flex and extend does the point of most contact with the tibia and the femur remain or change?
changes
43
Where is the point of contact of the TF throughout motion? What is this called?
always directly beneath the cruiciate ligaments | four bar linkage system?
44
How do arthrokinematics of the TF work during weight-bearing?
weight bearing: flexion: femoral condyles roll posteriorly and glide anteriorly on the tibial plateaus extension: femoral condyles roll anteriorly and glide posteriorly on the tibial plateaus
45
How do arthrokinematics of the TF work during non-weight-bearing?
non-weight bearing: flexion: tibial plateaus roll and glide posteriorly on femoral condyles extension: tibial plateaus roll and glide anteriorly on the femoral condyles
46
What is the ROM for flexion/extension in passive ROM, during gait, and stairs/sitting?
Passive: 20-0-160 degrees Gait: 0-70 degrees Stairs/sitting: 0-90 degrees
47
How is knee flexion/extension ROM affected by hip position?
knee flexion in supine (rectus femoris = quad) is different than prone (hamstrings) b/c they cross both joints
48
Where do most functional activities fall under with Flexion/extension ranges?
0-90 degrees | get person 0-90 ASAP after injury
49
What degree of adduction/abduction do you have in full knee extension? in 20 degrees flexion? Why is one more than the other?
8 degrees available ROM during extension b/c closed pack position; 13 available during 20 deg. flexion b/c open packed position
50
When sitting at 90 degrees, what is the total amount of internal rotation available? external? Combined?
Internal: 0-30 deg. External: 0-40 deg. total: 60 to 70 deg.
51
What is the screw home mechanism for the tibia? What kind of chain?
External rotation of the tibia on the femur during the last 20° of extension (open chain)
52
What is the screw home mechanism for the femur? What kind of chain?
Internal rotation of the femur on the tibia during the last 20° of extension (closed chain)
53
What are the three main reasons for the screw home mechanism?
Bony/meniscal structure: (medial femur and tibial condyles are longer AP) Ligament restrictions: ACL/PCL slight lateral pull (quads)
54
What is unlocking the knee?
internal rotation of the tibia on the femur during early flexion (NWB) via popliteus m.
55
Where is close packed position? What causes it?
Full extension creates maximal bony congruence and ligamentous tautness
56
Where is loose packed position? What causes it? Relevance to injury?
25 degrees of knee flexion minimal bony congruence ligaments lax minimal intra-articular pressure (ex. when landing from jump)
57
What provides TF joint stability?
joint capsule goes above the patella retinacula synovial lining
58
What are the cruciate ligaments' location and attachment?
intra-articular (inside joint), extra-synovial (synovial lining b/w ligament and synovial fluid; no blood supply) named according to their tibial attachment ACL: from anterior aspect of tibia posteriorly and laterally PCL: from posterior tibia and travels anteriorly and medially
59
ACL has how many bands?
two
60
Primary job of ACL?
Primary restraint to anterior translation of the tibia on the femur primary restraint to hyperextension
61
Secondary jobs (2) of ACL?
Assists with resistance to internal rotation of the tibia on the femur Assists with resisting varus and valgus forces
62
What is the maximum excursion at 30 degrees?
normal max ant. tibial translation at 5-8 mm
63
What is normal strain on the ACL? Failure?
2 to 4 % | 6 to 8 % is failure
64
At 90 degrees of knee flexion of isometric contraction of quad as hard as you can, any ACL strain?
no | posterior translation of tibia instead
65
At 30 degrees of knee flexion of isometric contraction, any ACL strain? Why is the strain the level it is?
yes anterior translation activation of quad less than full extension b/c hamstrings pull posteriorly and protect ACL (no quad pull anteriorly)
66
10 lbs knee extension 0 to 90 strain amt.? Why is the strain the level it is?
peak strain farther in extension (10 deg.) peak is 3.8% strain tibia is pulled anteriorly by patellar tendon (quads have larger vector and hamstrings have smaller vector)
67
how soon do open change post ACL reconstruction
start isolated 90 to 45 bc little strain after 3 to 4 weeks then full arcs
68
How prevalent are ACL injuries?
20% of all knee injuries | 70% non-contact
69
Why is the ACL more prone to injury in women?
women b/c structural factors: smaller in length, cross-sectional area, and volume biomechanical factors: Less stiff and fails at lower loads neuromuscular factors: Area occupied by collagen fiber is lower; peak in quad strength but less hamstring strength after puberty, slower m. activation pattern
70
What biomechanical differences can aid in preventing ACL injuries?
Higher knee valgus angles and moments Decreased Hip flexion angles and knee flexion stiffness during cutting Greater hip adduction Trunk adaptations (teach proper trunk position for knee loading) Hip transverse and frontal plane angles influence knee valgus moments
71
PCL location? Differences from ACL?
Runs from superior-anterior-medial (femur) to inferior-posterior-lateral (tibia) Shorter Less oblique Greater CSA (120-150%) (shorter, broader, less likely to tear than ACL)
72
What is the primary function of the PCL?
Restricts posterior translation of the tibia on the femur tear caused by plantar flexion with fall on tibia, sending it posteriorly
73
most common mechanism for ACL injury?
valgus collapse, anterior translation
74
precautions after PCL surgery?
limit active hamstring contraction for 3 to 4 mo.
75
What are the secondary functions of the PCL?
Assists with resistance to external rotation of the tibia on the femur Assists with resistance of varus and valgus forces

Unit 2 (29 decks)

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