Knee Flashcards
T/F: The knee is a bi-compartmental joint.
false, it’s tri-compartmental
Knee joint stability is dependent on what?
passive restraint structural integrity (strength of ligaments)
How many planes of motion does the knee move through?
2: sagittal and horizontal planes
What does the longitudinal axis of LE tell you? What’s a normal angle?
How straight up and down the leg is at the knee: 175 deg
- normally less than 180 since the angle of inclination makes the femur go in slightly (slight natural genu valgus)
With a mechanical axis of 150 deg, what does that tell you about the knee?
there’s a genu valgus at the knee: axis is less than 175
What would a genu varus do to the longitudinal axis value?
make it >170
What degree classifies a genu recurvatum?
> 10 degrees of hyperextension in the knee
What’s an example of a secondary passive-restraint knee stabilizer?
posterior capsule
Where is internal joint fluid pressure greatest in the knee?
at end ranges (is the least in slight flexion)
What is the position of comfort for the knee?
30 degrees flexion
What structures help make up the posterior capsule of the knee?
retinaculum comes from…
- vastus lateralis and medialis
- IT band
- popliteal oblique ligament
- arcuate oblique ligament
T/F: The tibiofemoral joint is inherently stable.
false- inherently unstable due to incongruent articular surfaces, leading to many knee injuries
What helps increase the articular congruency in the knee?
fibrocartilaginous menisci make tibial surface concave instead of flat; triples the tibiofemoral joint contact area
What do the medial and lateral menisci look like? What are they anchored by?
medial = lunar shape
lateral = C-shape
- anchored by the posterior horns
What is a tear of the posterior horns in the knee called? What can this lead to?
- bucket-handle tear, which is found in the inner-zone
* this can lead to unanchored menisci, = knee instability
If we didn’t have menisci, how much larger would the compressive forces be on our body?
200x larger, causing bone degeneration (osteoarthritis)
What is the primary function of the menisci? What else does it do? (4)
primary = to reduce tibiofemoral joint compression
- also does proprioception, joint stabilization/congruency, arthrokinematic guidance, and articular cartilage lubrication
Why is it so bad to tear the inner zone meniscus?
b/c it’s avascular and unlikely to heal; also nothing really anchoring menisci
Which is better, a peripheral tear or inner zone tear of the meniscus?
peripheral b/c it has a good blood supply
During what actions is the tibiofemoral joint most compressed?
- 4x compression during stairs
* 2.5-3x compression during walking
Weight bearing causes the menisci to wear down. Where does this occur?
on the periphery
What meniscus is more likely to tear? Why?
- medial is more likely to tear b/c it’s attached to MCL and doesn’t move as well
- LCL isn’t attached to the lateral meniscus due to the popliteal ligament, so it’s more moveable
How many degrees of freedom do we get at the tibiofemoral joint?
2: flex/extend and IR/ER
What ROM do we get for KE and KF?
KE = 0-10 degrees hyperextension, common in females KF = 130-150 degrees
Why can we not get an exact measurement with a goniometer when measuring KE or KF? What landmark do we use to estimate?
- The ML axis of rotation migrates as we move through motion, following the condyle curves
- since the axis moves, this alters the moment arm of the muscles, so we have to just estimate the axis at the LATERAL EPICONDYLE
At what knee position do we get maximal IR and ER? Which do we get more of?
- when knee is flexed to 90 = max rotation
- get 2x more ER than IR (40-45 deg total)
What landmark do we use to measure rotation of the knee, and what’s it relative to?
tibial tuberosity either pointing out or pointing in, relative to femur (foot will also be pointing either in or out usually)
Describe the arthrokinematics of open chain knee extension. What happens with the menisci during this?
tibia on femur = concave on convex
- rolls and slides anterior
- menisci are pulled anterior also via quads
Describe arthrokinematics of closed-chain knee extension.
femur on tibia = convex on concave
- roll anterior, slide posterior
Describe the arthrokinematics of the knee in a downward squat.
femur on tibia = convex on concave
- posterior roll, anterior slide
What is the screw-home mechanism? What 4 things allow this to occur?
screw-home = last 30 deg of KE need rotation to occur
- this is possible via:
- popliteus muscle to unlock
- medial condyle more anterior than lateral
- lateral pull of quad
- passive tension in ACL
To lock the knee, what needs to occur? in open and closed chain
open chain lock = tibia ER
closed chain lock = femur IR
What unlocks the knee? How does it do this?
popliteus either:
- open chain unlocks = brings tibia into IR
- closed chain unlocks = pulls femur out to ER
How can you tear the ACL? (via what extreme motions)
via hyperextension and ER
T/F: The knee externally rotates slightly to unlock.
false, knee slightly internally rotates to unlock
- but this can be either through IR of tibia or ER of femur, depending on what’s fixed
T/F: Knee must be flexed to maximize independent IR/ER.
true
T/F: Menisci get deformed with femur on tibia rotation.
true, due to compression over time
T/F: You can get some rotation in full KE.
false, none at all. Need knee flexion
How are menisci stabilized?
by the posterior horns and their connecting muscles (popliteus and semimembranosis)
What ligament(s) primary function is to restrain frontal plane motion?
LCL/MCL
Where is MCL stressed the most?
in its DEEP fibers with valgus stress (vs superficial fibers)
- these deep fibers blend with the medial meniscus
T/F: MCL and LCL both restrain IR/ER.
true
When are the MCL and LCL both taut?
in knee extension
What ligament(s) give multiplanar stability to the knee and guide it’s natural kinematics?
ACL/PCL
What kind of receptors do the ACL and PCL have a lot of? What is this for?
ACL/PCL have lots of mechanoreceptors, giving proprioception to the knee about where it is in space
What regulates muscle contraction force?
the mechanoreceptors in the ACL/PCL; can limit muscle force
T/F: ACL and PCL both limit rotation.
true
What kind of rehab, besides strengthening, is essential for ACL/PCL tears and why?
neuromuscular rehab is SO important b/c you’ve not only lost stability , but also the mechanoreceptors that tell the knee where it is in space
- without this, it’s difficult to control muscle force when needed, and the ligaments can tear again
- tell a pt to reposition their knee (like you showed them) with their eyes closed -> they struggle with this
At what degree does the tibia begin to anteriorly slide in KE?
last 50-60 degrees of KE; roll first
What limits posterior translation of the femur?
ACL
What is the agonist to the ACL?
hamstrings b/c help limit tibial anterior translation
How can the ACL give rotary stability?
via its oblique orientation
What is the gold standard for ACL reconstruction? When would this not be used?
gold standard = patellar tendon graft
- however this takes a long time to take, so for younger athletes, a hamstring tendon graft is a quicker option
T/F: Most ACL injuries involve contact with something else.
false, 70% are non-contact
What are the 3 common factors of ACL injury?
females more affected by ACL tear due to:
- a greater genu valgus
- greater femoral IR
- strong quad contraction
What is the “valgus collapse”? How can you train people to avoid it?
When a person (often female) jumps and then lands hard into valgus, stressing their ACL and MCL (femur IR and ad)
- train people to land with their knees bend, but land with them straight and not falling inwards
- teach proper step-down as well, with knee straight over foot and not falling medially
- strengthen ERs (like glutes) to prevent IR of femur
What do many cases of ACL tear result in if proper body mechanics aren’t taught?
50% of cases end up with osteoarthritis
What is the unhappy triad? How does it occur?
injury to ACL, MCL, and medial meniscus (as well as post. capsule)
- occurs via hyperextension of knee when foot is fixed, coupled with valgus or rotary stress
- so bad b/c quad is activating, along with passive stretch of ACL = lots of force bringing tibia anterior
When is the ACL at maximum passive tension?
full knee extension
When is the PCL at maximum passive tension? Where is it most lax?
- between 90-120 degrees of flexion = max strain
- lax between 30-40 degrees flexion
What’s the normal ROM for knee flexion?
130-150 degrees of flexion
T/F: PCL is most lax in knee extension.
false, lax in 30-40 degrees flexion
Could you strengthen quads in a patient that just tore their PCL?
yes for SURE, do popliteus too
About 50% of PCL injuries involve what other 3 structures?
- ACL
- Meniscus
- posterolateral capsule
Where is the patella at its most freely-moving point?
full KE
When does the patella do the moving in KE/KF, in open or closed chain?
- OPEN CHAIN = patella slides on intercondylar groove and follows tibia
- close chain = intercondylar groove of femur glides on fixed patella
Describe when the patella experiences inferior pull, superior pull, etc.
full KE = only inferior pull
full flexion = superior pull
midrange = superior and inferior pull
What makes up the superior pull? Inferior pull?
superior pull = lateral facet and odd facet
Why is lateral dislocation of the patella more likely than medial?
quad pulls laterally, so does IT band
What nerve innervates the knee extensors?
femoral n.
What nerve is the largest afferent supply to the knee joint?
tibial n.
Which of these does not innervate the knee flexors?
a) tibial n. b) superficial fibular n. c) common fibular n. d) femoral n. e) obturator n.
b) superficial fibular
What does tibial nerve innervate?
posterior compartment of leg
- superficial = gastroc, soleus, plantaris
- deep = popliteus, deep tibialis posterior, FHL, FDL
What does common fibular nerve innervate?
branches into superficial and deep, so those are:
- superficial = lateral compartment (peroneus long/brevis)
- deep = anterior compartment (tib anterior, EDL, EHL)
Foot dorsiflexors are innervated by what?
deep fibular n. (muscles = tib anterior, EDL, EHL)
What nerve roots give sensory innervation to the knee?
L3-5
Why can’t you just strengthen the vastus lateralis to decrease lateral patellar tracking?
b/c vastus medialis can’t be isolated: need to just strengthen entire quad
- could do just medialis through e-stim though
T/F: Passive tension of the patellar ligament offsets quad torque during KE.
true
What is patella tracking?
how the patella moves in the intercondylar groove of the femur: want it to be smooth and stay in there
What do the quads do eccentrically? (2)
- control the amount of KF, especially in a squat
- act as shock absorber to attenuate ground reaction forces, countering KF
Do we need quads to get out of a chair?
yes, duh
What are the quads doing in an isometric contraction? (for the knee joint)
giving stability and protection
When running, what is a big thing the quads need to do?
control knee flexion! When you hit the ground, you go into knee flexion to absorb the GRF, and the quads control this
Where is the most demand on the quad in open chain? Closed chain?
open chain = quad is in highest demand in full KE
closed chain = quad is in highest demand in 90 degrees KF
When do the internal torque of extensors match the external torque of the body weight in rising from a squat?
at 45-70 of knee flexion
Why start a patient in low squats vs deep squats for quad strengthening?
- not as much internal torque needed from knee extensors to offset external torque (of the knee flexors and body weight) when in only 40-70 degrees of knee flexion
- easier to do these small squats if quads can’t produce enough torque to offset high extensor torque in a deep squat
- good to train this way for patella as well, gives it good contact
What helps increase the internal moment arm for the quads? What 3 factors influence the length of the IMA? (including patella)
patella increases quad pull by 5-10x:
- shape and postion of patella
- shape of distal femur including intercondylar groove depth
- migrating axis of rotation
What is extensor lag?
the last 20 degrees of extension are difficult for patients because they require a lot of quad torque
T/F: Upper body weight moment arm increases from 0-90 degrees knee flexion in closed chain.
true
Organize these in terms of decreasing patellar joint compression force: stair climbing, SLR, walking, deep squat.
deep squat -> stairs -> SLR -> walking
Compression force magnitude on the patella is a function of what two things?
quad contraction and knee flexion angle
When is patellofemoral joint compressive force maximized?
60-90 degrees flexion
T/F: The amount of contact with the patella decreases in a deep squat.
true
What is the Q-angle and what’s a normal value for it?
- q-angle = angle from line through ASIS to patella, and line from patella to tibial tuberosity; determines quad lateral pull
- normal = 13-15 degrees (females can be larger than males)
A larger Q-angle can lead to what at the knee? (or visa versa)
valgus
What general factors offset the lateral pull of the patella, keeping the patella in the groove?
1) local factors = those acting directly on PFJ
2) global factors = those related to alignment of LE bones and joints distal to PFJ
What are the 3 local factors helping to offset lateral pull of patella?
- VMO in good alignment to keep patella medial
- medial patellar retinacular fibers that blend w/ VMO pull medially
- raised lateral facet of intercondylar groove prevents lateral pull
Explain the global factors affecting the lateral patellar pull.
These things increase Q-angle, which increases lateral pull:
- weak hip abductors: adductors pull femur in, cause valgus
- hip adductor tightness
- coxa vara
- excessive subtalar joint eversion
T/F: PT can affect the local factors for patellar issues.
false, only global
What can a PT do to address the global factors for patellar pull?
- strengthen abductors to decrease genu valgus potential
- stretch adductors
- raise arch of foot
T/F: Excessive ER of knee can decrease the Q-angle and decrease lateral bowstring force on patella.
false, ER can increase bowstring force on patella by increasing Q-angle
How do you increase bowstring force? (bad)
IR of femur, ER of tibia
Why do we not just IR the knee to decrease bowstring force?
b/c it will result in foot pronation
What muscles resist valgus loading of the knee?
pes anserine:
- ST
- gracilis
- sartorious
T/F: Popliteus does lateral rotation of femur.
true
T/F: The hamstrings are dependent on moment arm to generate force.
FALSE
What actions does the pes anserine muscles do?
all flex and IR knee
What does the biceps femoris do?
flexes and ER knee
What has eccentric control over the ER of the tibia during knee extension?
the internal knee rotators
What needs to happen during early swing phase for the LE to clear the floor?
concentric knee flexion
