10-17b Knee Biomechanics II Flashcards by Josie Hornig

Describe the MCL. What is its clinical significance?

It has three layers, blends in with the joint capsule

attaches above medial condyle of the femur and below the medial surface of the shaft of the tibia

force to failure = 799 N

more stable, less mobile, stabilizes medial meniscus = medial meniscus is less mobile and more prone to injury

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What is the primary job of the MCL? At what degree of knee flexion is it contributing most to valgus stability?

resist valgus forces = valgus stress test
limits external rotation of tibia

resists anterior translation of tibia on femur

at 25% of knee flexion MCL contributes 78% of valgus stress (do stress test here)

at 5% it contributes less

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When is the MCL taught? What is its structure when extended and flexed? Clinical significance?

taut at full knee extension: helps resist hyperextension

superficial vertical fibers relaxed and oblique fibers are taut during extension

superficial vertical fibers are tight and deep oblique fibers are relaxed during flexion

More injuries when extended due to it being taught

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Define Q-angle. Normal degrees?

Angle from ASIS (where sartorius attaches), to midline patella, to tibial tubercle

13-15 degrees

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Where does the LCL attach? Force to failure? Variations?

attaches to proximal/posterior femoral condyle & distal/anterior styloid-fibula

392 N

100% variation

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What are the LCL’s primary jobs? Where is it taught?

resist external rotation of the tibia on the femur

taut in full extension

helps resist hyperextension

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What is the function of the IT band? Where does it insert?

Anterolateral support to the knee
Gerdy’s, lateral patella femoral ligament

Knee extension
(IT Band is anterior to knee axis)

Knee flexion
(IT Band is posterior to knee axis)

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What is the primary job of the posterior capsule?

Resists excessive hyperextension

Genu Recurvatum:
Hyperextension greater than 5°

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What is the function of the PLC

resists varus stress, external rotation, and posterior translation

dial test

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What is the PLC three major stabilizers?

LCL
Popliteo-fibular ligament (PFL)
Popliteus muscle and tendon

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What is the PLC’s secondary stabilizers?

Fabello-fibular ligament (FFL)
Joint capsule
Long head of biceps
ITB

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What is the function of the posteromedial corner?

Anteromedial rotary stability

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What are the three heads of the hamstrings? What are their primary function?

semimembranosus (medial meniscus)
semitendinosus (pes sanserine)
biceps femoris (attaches to fibula)

flex the knee and stabilizes the hip

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Pes Anserine components? Where is it?

Sartorius (anteriorly, Gracilis Middle, Semitendinosus (most lateral)

Anteromedial knee

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Knee Extensors: quads

passes over two joints
Rectus femoris
vastus lateralis 
vastus medialis
vastus intermedius

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What indicates quad weakness? Where do ind. compensate?

Less knee flexion during weight acceptance

less force attenuation
greater TF compressive forces

compensate at hip and ankle

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What side of the knee has a buttress for the patella?

lateral

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apex attaches to what tendon?

patellar tendon

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Base attaches to what tendon?

quadriceps tendon

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What are the facets on the posterior patella?

odd facet, medial facet, vertical ridge, lateral facet

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Is patellofemoral arthritis as prevalent as TF arthritis? What population?

yes

especially in post traumatic knee populations?

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What plays a part in lateral patellar dislocation

IT band on top of retinaculum to keep patella from moving laterally

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How does the q angle affect the tendency towards lateral sublux of patella

all the tendons are oriented laterally, so the patella tends to move laterally

females have more patellar subluxations

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What does normal alignment use?

angle b/w femur and tibia

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knee abduction

ankle pronation

What is a dynamic valgus vs. alignment valgus?

vectors are more lateral

What m. prevent lateral patellar dislocation?

quadriceps: vastus medialis, vastus medialis obliqus, and VMO combat q angle

What's the pennation angle

vastus medialis m. VML = 15-18 degree pennation angle to pull patella superiomedially VMO = 37 degrees VMO patella = 50-55 degree pennation angle fights lateral translation

Which side of the trochlea is heightened?

lateral

What are the static stabilizers against lateral translation?

lateral trochlea, medial PF ligament (biggest thickening structure on the medial structure of the knee that provides static stability, medial retinaculum

What does a hypoplastic trochlear groove lead to?

chronic dislocation

What should you train athletes to do to utilize the trochlea best?

have them flex their knees | the patella is out of the trochlea for the first 15 to 20 degrees of flexion

What structures stabilize against medial translation

vastus lateralis, lateral retinaculum (attached to IT band)

What are the proximal and distal stabilizers?

quad, quadriceps tendon (broad attachment) | patellar tendon to tibial tuberosity

infrapatellar fat pad role?

fat pad pathology adipose tissue: highly innervated so can be a source of knee pain abnormal loads through the fat pad causes thickening nothing to do with stability

What is patella alta/baja? clinical relevance?

alta: high knee cap baja: low knee cap length of patellar tendon to the tibial tubercle over length of patella = should be 1 greater than 1.2, knee cap is sitting higher clinical relevance: if it sits high then its more likely to subluxate (not engaging trochlea until far more knee flexion) shallow groove and high sitting patella: patella femoral joint problems

What are normal patellar kinematics?

``` proximal/distal translation anterior posterior translation flexion/extension med/lat translation med/lat tilting med/lat rotation ```

Where does the patella move when you extend your knee?

Located above joint line Moves proximal anteriorly, Patella extends

Where does the patella move when you flex your knee?

Moves distally, posteriorly, flexes

Where does the patella normally tilt?

laterally due to IT band

What are normal patellar kinematics from extension to flexion? Why for each?

medial: 0-30 degrees: engages in trochlear groove lateral: 30-100 degrees medial > 100 degrees: medial patellofemoral ligament gets taught

What is the contact area of the patella from the beginning of flexion? What comes into contact in deep flexion? Clinical significance?

contact on distal end As flexion approaches 90 degrees, the articulating surface moves towards the base to cover the proximal one half of the patella At 135 degrees of flexion, the odd facet comes into contact pain can be different depending on the degrees of flexion

How does contact area change from 0 to 90 degrees knee flexion?

0.8 cm squared to 4.7 cm squared

In a straight knee, what two forces are acting on the patella?

patellar tendon and quadriceps force

As you start to squat what m. is working harder?

quad

What happens to JRF as you go deeper into a squat?

higher

How can you reduce someone's JRF?

bring weight backwards towards heels to reduce quad work and bring glutes into play

For exercise prescription, what should you avoid?

deep squats

In open chain, where do you see an increase in quad force?

last 20 deg of extension

What is JRF for patellofemoral joint?

Function of knee flexion and task, moment arms of Pat lig, Quad Tendon, Moment arm of patella, quadriceps force

What is PFJ stress equal to?

JRF/contact area

What is PFJ stress at extension at zero deg in regards to JRF and contact area for lex extension?

high JRF/low contact area | high stress

What is PFJ stress at 30 deg flex in regards to JRF and contact area for leg extension?

lower JRF (less quad effort)/higher contact area

What is PFJ stress at 90 deg flex in regards to JRF and contact area for leg extension?

lowest JRF (no quad activation)/highest contact area

What is PFJ stress at 0 deg flex in regards to JRF and contact area for leg press?

small JRF/small contact area

As you begin to squat, what happens to PFJ stress at 30 deg flexion in regards to JRF and contact area for leg press?

higher JRF/higher contact area

Why does stress go up in a squat at 90 deg as surface are increases along with the JRF?

quads are working harder JRF is big/large contact area JRF are significantly higher than the forces from change in contact area stress goes up

What is the prevalence of PFPS?

all encompassing diagnosis indicates overuse chronic anterior knee pain highly prevalent 22.7 percent pop anually having this younger develops into arthritis later on

What are the mechanisms of PFJ pain?

local factors, distal factors, proximal factors | the knee is the symptom, but the problem can be somewhere else

What proximal factors can cause PFJ pain?

hips dropping in frontal plane brings femur into adduction which causes valgus

What are the local factors that cause a lateral pull on the patella?

quad force IT band patella position (alta)

What are the local factors that oppose a lateral pull on the patella?

lateral trochlear grove (hypoplastic) VMO (atrophy, inhibition, delayed activation?) medial PF ligament/retinaculum

What kind of moment can be assoc. with PFP?

higher knee abduction moments

What does pronation of the foot do?

alters biomechanics at the knee and hip

What are the dynamic stabilizers against lateral translation?

pennation angle m. located medially that resist lateral translation VMO patella at 50 to 55 deg CMO quad tendon at 37 deg CML at normal 15 to 18

What direction of a vector of force is caused by the patellar and quad tendons on the patella?

lateral vector