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AFAB II > Lecture 8: Knee kinematics > Flashcards

Lecture 8: Knee kinematics Flashcards

1
Q

the capsule encloses what joints

A

medial and lateral tibiofemoral joints and patellofemoral joint

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2
Q

anterior reinforcement of knee

A

patella and tendon

connective tissue is reinforced by medial and lateral retinacular fibers (extensions of ITB, vastus lateralis and medialis, and connections to femur, tibia, patella, quads, patellar tendon, collateral ligaments, and menisci)

muscular reinforcement via quads

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3
Q

lateral reinforcemenrt of knee

A

connective tissue reinforcement via LCL, lateral patellar retinacular fibers, and ITB

muscular reinforcement via biceps femoris, tendon of popliteus, and lateral head of gastroc

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4
Q

posterior reinforcement of knee

A

connective tissue: oblique popliteal ligament, arcuate popliteal ligament

muscular: popliteus, gastrocs, hamstrings (especially semimembranosus)

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5
Q

posterior lateral reinforcement of knee

A

connective tissue: arcuate popliteal lig, LCL, popliteofibular lig

muscular: tendon of popliteus

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6
Q

what is the fabella

A

sesamoid bone in posterolateral capsule of human knee joint

presence is variable

located in posterior aspect where lines of tensile strength intersect

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7
Q

medial reinforcement of knee

A

from patellar tendon to posterior capsule medial side

connective:
-anterior 1/3 = thin fascial layer; medial patellar retinacular fibers

-middle 1/3 = medial patellar retinacular fibers, superficial and deep MCL

-posterior 1/3 = thick; starts near adductor tubercle blends with SM tendinous expansion and post capsule and post oblique lig; pes anserines reinforces

musclular = semimembranosus, SGT? - pes anserines

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8
Q

the internal capsule is lined with what

A

synovial membrane

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9
Q

how many bursae in knee

A

14 at inter tissue junctions that encounter friction with motion

some are extensions of synovial membrane, some are external to capsule

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10
Q

what are the fat pads present in the knee

A

suprapatellar and deep infrapatellar

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11
Q

describe the TF joint

A

large convex femoral condyles and flat, smaller, tibial plateaus

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12
Q

describe motion of TF joint/how injuries occur

A

excessive motion present but soft tissue provides stability

means injury can involve many structures

menisci acts as gasket to form seats for femoral condyles

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13
Q

describe how the menisci lay

A

anchored to intercondylar region of tibia at anterior and posterior horns

external edge of each is attached to tibia at capsule bu coroncary ligaments (meniscotibial) - allows pivoting

2 menisci connected anteriorly by transverse lig

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14
Q

what muscles have secondary attachments to menisci that help stabilize

A

quads (both menisci)

semimembranosus (both)

popliteus (lateral)

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15
Q

describe the differences between the 2 menisci

A

medial is oval shape and attaches to MCL and adj capsule

lateral is circular and only attaches to lateral capsule

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16
Q

where does popliteus run

A

passes between LCL and lateral meniscus

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17
Q

describe the blood supply to the menisci

A

peripheral is 1/3 from direct genicular arteries (off popliteal) = the red zone

inner 2/3 is avascular = white zone

nutrition is from synovial fluid

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18
Q

primary functional consideration for tibiofemoral joint

A

decrease compressive forces (triple joint contact area to decrease pressire on articular cartilage)

WB is axial; meniscus deforms peripherally = tensile stress

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19
Q

describe compressive forces at knee while walking

A

2.5-3x body weigth at knee and > 4x with stairs

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20
Q

weight bearing at knee with cycling

A

1.2x BW

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21
Q

complete lateral meniscectomy increases contact pressure by how much

A

230%

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22
Q

how much load goes through the medial and lateral compartmetns of the knee

A

70% load goes through lateral

50% of that in the medial goes through the meniscus

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23
Q

secondary functional considerations for tibiofemoral joint

A

stabilizing through joint motion

lubricating articular cartilage

providing proprioception

help guide arthrokinematics

24
Q

common mechanisms of injury for meniscus

A

often associated with forceful, axial RT of femoral condyles over flexed WB knee (can pinch/dislodge meniscus)

a dislodged or folded flap (bucket handle) can mechanically block knee

medial is injured 2x as frequently via valgus force (large stress on MCL/post-med capsule)

risk increases with lig laxity (esp ACL) and malalignment

loss of hoop stress capacity with meniscal tear (especially with tear at medial posterior horn)

25
Q

osteokinematics if flexion and extension of knee

A

2 deg of freedom

knee slightly flexed for RT to occur

frontal plane is passive only (6-7 deg)

with flex/ext IAR moves

130-150 flex and 5-10 hyperext

26
Q

what are the biomechanical implications of the IAR or evolute

A

lengthens the moment arm of the flexor and extensor musculature

brace might piston; need to align to the average axis the lateral epicondyle

27
Q

osteokinematics of IR and ER

A

longitudinal axis through tibia (influened by sagittal plane motion) little in ext

at 90 deg flex: 40-45 deg axial RT

ER 2:1 exceeds IR

RT is named by position of tibial tuberosity relative to the ant distal femur

28
Q

describe arthrokinematics of tibio on femoral ext

A

tibia rolls and slides anteriorly on femur

meniscus is pulled anteriorly by quads

29
Q

femoral on tibial ext arthrokinematics

A

femoral condyles roll anteriorly and slide posteriorly on tibia

quads direct the roll and stabilizes the meniscus vs posterior shear of femur

30
Q

describe the screw home mechanism

A

full ext requires 10 deg ER during last 30 deg of ext (conjuct RT is linked; not independent motion)

increases joint congruency/stability

open chain = tibia ER

closed chain = femur IR

31
Q

screw home is driven by

A

shape of femoral condyle (tibial follows medial condyle and creates ER)

passive tension in ACL

slight lateral pull of quads

32
Q

how does screw home mechanism occur with flx

A

unlocking IR happens first

driven by popliteus (can RT femur or tibia)

33
Q

arthrokinematics of IR and ER at knee

A

knee must be flexed

spin between menisci and articular surfaces of tibia and femur

axial RT of femur over tibia causes menisci to deform/compress

popliteus and SM help stabilize

34
Q

describe the MCL

A

flat and broad; has superficial and deep parts

superficial = well defined parallel fibers at 10 cm med epicondyle to medial patellar retinaculum fibers to medial proximal tibia (just post to pes anserine)

deep = slightly post and distal; shorter and oblique attaches to capsule/medial meniscus/SM tendon

35
Q

describe the LCL

A

short cord like

runs vertical from lateral epicondyle of femur to head of fibula

doesnt attach to adj meniscus (popliteus runs between)

blends distally with biceps femoris tendon

36
Q

primary functional consideration for MCL and LCL

A

they function to limit motion in frontal plane

MCL vs valgus force and LCL vs varus

37
Q

secondary function of MCL and LCL

A

provide general stabilizing tension (especially walking near ext and loading)

protect against RT extremes (MCL at extreme of ER); i.e. planting R foot and body cut L

38
Q

describe the ACL and PCL

A

cross within intercondylar notch
intracapsular
covered by extensive synovial membrane
poor blood supply
named for attachment on tibia
thick/strong

39
Q

ACL in youth can withstand how much force

A

405 lb or 1800 N

40
Q

what do the ACL and PCL restrict

A

resist all extremes of motion

primarily AP shear forces between tibia and femur

cutting in sagittal plane motions

help guide arthrokinematics and provide proprioceptive feedback

41
Q

describe the ACL

A

anterior tibia

runs posterior and superior and laterally toward the medial side of the lateral condyle

collagen fibers twist on each other (2 sets; ant med and post lat)

at any given point some fibers are taut in flex but increasingly taut as they reach ext

specifically the post lat bundle along with the post capsule, knee flexor muscles, and parts of the collateral lig)

42
Q

describe what happens with the ACL during the last 50-60 deg ext

A

force of quads pulls tibia ant and thus tension in ACL limits slidegl

43
Q

what is the ant drawer test

A

leg in 90 deg

pull proximal tibia ant

ACL is 85% of passive resistance to ant glide

8mm or 1/3in greater translation than contralateral LE = possible tear

HS spasm may prevent a good test

44
Q

common mechanisms of injury for ACL

A

highly vulnerable if tensioned in extremes of motion; especially those with high velocity

factors
-speed/direction of GRF
-amount/direction of compressive and shear forces
-control/timing of muscular forces
-integrity and stength of tissues
-alignment of trunk and lower limb

transient sublux with secondary trauma (menisci, cartilgage, MCL, etc)

chronic instability and further degeneration

hyperext

limited ER and ABD

45
Q

most frequently ruptured ligament in knee

A

ACL

half in ages 15-25 with high velocity sports

46
Q

what does it mean that 70% of sports related ACL injuries are non contact

A

landing, decelerating, cutting, pivoting over single limb

47
Q

how is strong quad activation related to ACL injury

A

valgus collapse

excessive ER (femur is internally rotated)

48
Q

describe the PCL

A

slightly thicker than ACL

post tibia to lateral medial femur

2 primary bundles

twists and changes length and orientation with flexion

some fibers taut in flx and ext but the majority of PCL becomes increasingly taut with greater flex (90-120)

slack in 30/40 into ext

posterior glide - tibia partially limited by PCL

49
Q

describe the post drawer test

A

proximal end of tibia posterior

knees in 90 flex

limits ant translation of femur

rapid descent into deep squat

sag at 90/90

50
Q

common mechanisms of injury with PCL

A

high energy trauma

rare; 2-10% all knee injuries

falling onto a fully flexed knee “dashboard injury”

51
Q

kinematics of the patallofemoral joint

A

articular side of patella and trochlear notch

stabilizer = quads

Can cause chronic anterior knee pain/degeneration

tibial on femoral = patella slides relative to fixed trochlear groove (patella pulled toward tibia)

femoral on tibial (squat) = trochlear groove slides relative to fixed patella (held by eccentric quads and patellar tendon)

52
Q

desribe patellofemoral contact at 135 deg flexion

A

superior pole below the groove at the lateral and odd facets

53
Q

patellofemoral contact at 90-60 flexion

A

in trochlear groove

contact area greates (still only 1/3 area)

54
Q

patellofemoral contact at 20-30 deg flexion

A

contact at inf pole

lost much of the mechanical engagement with groove (45% of that 60 deg)

55
Q

patellofemoral contact with full ext

A

rests completely prox to groove on suprapatellar fat pad

if quads are relaxed patella moves freely

AFAB II (14 decks)

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