10-17b Knee Biomechanics II Flashcards
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
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
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
Define Q-angle. Normal degrees?
Angle from ASIS (where sartorius attaches), to midline patella, to tibial tubercle
13-15 degrees
Where does the LCL attach? Force to failure? Variations?
attaches to proximal/posterior femoral condyle & distal/anterior styloid-fibula
392 N
100% variation
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
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)
What is the primary job of the posterior capsule?
Resists excessive hyperextension
Genu Recurvatum:
Hyperextension greater than 5°
What is the function of the PLC
resists varus stress, external rotation, and posterior translation
dial test
What is the PLC three major stabilizers?
LCL
Popliteo-fibular ligament (PFL)
Popliteus muscle and tendon
What is the PLC’s secondary stabilizers?
Fabello-fibular ligament (FFL)
Joint capsule
Long head of biceps
ITB
What is the function of the posteromedial corner?
Anteromedial rotary stability
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
Pes Anserine components? Where is it?
Sartorius (anteriorly, Gracilis Middle, Semitendinosus (most lateral)
Anteromedial knee
Knee Extensors: quads
passes over two joints Rectus femoris vastus lateralis vastus medialis vastus intermedius
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
What side of the knee has a buttress for the patella?
lateral
apex attaches to what tendon?
patellar tendon
Base attaches to what tendon?
quadriceps tendon
What are the facets on the posterior patella?
odd facet, medial facet, vertical ridge, lateral facet
Is patellofemoral arthritis as prevalent as TF arthritis? What population?
yes
especially in post traumatic knee populations?
What plays a part in lateral patellar dislocation
IT band on top of retinaculum to keep patella from moving laterally
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
What does normal alignment use?
angle b/w femur and tibia
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
