Knee region Flashcards
What is normal genu valgus?
- 170-175 degrees
- the angle the femur and tibia make in relation to the outside of the leg
What is excessive genu valgus?
- less than 170 degrees (knock knee)
- leads to hip adduction and ankle pronation
What is genu varum?
- greater than 180 degrees (bow legged)
- leads to hip abduction and ankle supination
What are all the tissues that connect to the medial meniscus?
- MCL
- coronary ligaments
- quads
- semimembranosus
- medial joint capsule
What are all the tissues that connect to the lateral meniscus?
- popliteus
- coronary ligaments
- quads
- semimembranosus
- lateral joint capsule
- posterior meniscofemoral ligament
What are the main functions of the menisci?
- decrease compression
- stabilize joint
- lubricate cartilage
- proprioception
- guide arthrokinematics
Why can’t the menisci heal very well?
- only vascularized on outer 1/3rd
Which meniscus is more frequently injured?
- medial meniscus
- has more attachments so doesn’t move as freely as lateral one
Why would active hamstring strengthening after a fresh meniscal surgery potentially be detrimental to the tissue?
- semimembranosus attaches to BOTH menisci so a fresh repair could be torn with hamstring activation
How is knee rotation named?
- axial rotation by tibial tuberosity relative to distal anterior femur
- tibial-on-femoral ER: tibia ER’s on fixed femur
- femoral-on-tibial ER: femur IR’s on fixed tibia
What are the arthrokinematics of tibial-on-femoral knee extension
Concave tibia rolls and slides anterior
What are the arthrokinematics of tibial-on-femoral knee flexion
concave tibia rolls and slides posterior
What are the arthrokinematics of femoral-on-tibial knee extension
convex femur rolls anterior and slides posterior
What are the arthrokinematics of femoral-on-tibial knee flexion
convex fmeur rolls posterior and slides anterior
What is the Screw-Home mechanism of the knee?
- obligatory ER of the tibia of about 10 degrees in the last 30 degrees of knee extension
Describe the movement that occurs in the last 10 degrees of knee extension
- the tibial tubercle moves into alignment with the lateral femoral condyle
What factors cause the Screw-Home mechanism?
- shape of the medial femoral condyle
- passive tension in ACL
- slight lateral pull of quads
What is the primary guiding mechanism for the screw home movement of the knee?
- medial condyle shape
How does the knee get out of the Screw-Home position?
- popliteus “unlocks” the knee to IR for flexion from fully extended position
If the foot is planted and a valgus force is applied to the knee, what structures could be damaged?
- MCL
- Posterior medial capsule (PMC)
- ACL
What injury is the MCL most vulnerable to?
- closed chain + full EXT + valgus force + extreme ER
What do the MCL and LCL resist?
- MCL: resists valgus
- LCL: resists varus
What knee ROM makes the ACL most taut?
- posterior lateral bundle is full extension
What affect does quad activation have on the ACL & in what ROM?
- during last 50-60 degrees of knee extension they pull tibia anteriorly
- causes ACL to become taut
- quads are the ACL’s antagonist
What knee motion makes the PCL most taut?
- knee flexion
- peak at 90-120 degrees
What affect does hamstring activation have on the PCL & in what ROM?
- hamstrings are the PCL’s antagonist
- pulls it taut in about 90-120 degrees of knee flexion
What is the most common mechanism of injury for the PCL?
- high-injury trauma
- falling on the knee or car crash (“dashboard” injury)
How is the patellofemoral joint stabilized?
- quads
- articular fit
- surrounding soft tissue
In which position is the patella least stable?
- full extension w/ quads relaxed
How does the patella move during knee flexion & extension?
T-on-F:
- flex: patella slides inferior
- ext: patella slides superior
F-on-T:
- trochlear groove slides beneath patella
When in the ROM does each part of the patella contact the trochlear groove?
135 flex: facets contact groove
90 flex: superior pole
60-90 flex: most contact area
20-30 flex: inferior pole
0 flex: contacts suprapatellar fat pad
What structures make up the knee extensor mechanism?
- quads
- quad tendon
- patella
When in the ROM are quad torques largest for open chain knee extension?
- 45-70 degrees knee flexion
When in the ROM are quad torques largest for closed chain knee extension?
- 90-45 degrees knee flexion
How does the patella enhance quad function?
- increases IMA of knee extensor mechanism
- increases greatest amount of torque we can produce
What are the 3 factors influencing the moment arm of the knee extensor mechanism?
- shape and position of patella
- shape of distal femur
- migrating AoR
What affect does quad stress have on different impairments?
Damages w/:
- patellofemoral pain
- OA
Therapeutic w/:
- healthy
- late phase ACL rehab
Why does extensor lag occur?
- weakness of quads that fails to full extend the knee
- usually after surgery or trauma to knee
- swelling increases intra-articular pressure which inhibits neural activation of quads
Why does PFJ compression increase with deeper squatting?
- deep squats decreases the angle of pull of the quads which increases magnitude of force directed into the trochlear groove
What are some local factors that could cause patella mal-tracking in the trochlear groove?
Lateral bowstringing
- ITB or lateral patellar retinacular tightness
flatten lateral trochlear groove
patella alta (high patella)
atrophied VMO (w/ rest of quads)
ruptured medial patellar retinacular fibers
What are some global factors that could cause patella mal-tracking in the trochlear groove?
Excessive genu valgum
- weak hip abductors
- tight hip adductors
Excessive knee ER
- weak hip ER’s + abductors
- tight hip IR’s + adductors
When during knee ROM do the hamstrings have the best leverage?
50-90 degrees knee flexion
When during knee ROM do the hamstrings generate the best torque?
20 degrees knee flexion
Why are the hamstrings best leverage position different from their greatest torque position?
- the length-tension relationship is essential when looking at torque potential
- it is optimal when lengthened (20 degrees knee flexion)
What is the active and passive insufficiency for the quads?
Active:
- hip flexion + knee extension
Passive:
- hip extension + knee flexion
What is the active and passive insufficiency for the hamstrings?
Active:
- hip extension + knee flexion
Passive:
- hip flexion + knee extension
What are some detrimental effects of Genu Varum?
- increases medial joint loading -> greater loss of joint space -> greater knee adduction -> increased strain on LCL
What are some detrimental effects of Genu Valgum?
- MCL + medial capsule stress
- patellar maltracking
- ACL stress
- lateral compartment OA leading to knee replacement
What are some potential causes of Genu Valgum?
- previous injury
- high BMI
- ligament laxity
- weak hip abductors
- excessive foot pronation
What are some detrimental effects of Genu Recurvatum?
10 degrees extended beyond neutral
- posterior structure laxity
- altered arthrokinematics while walking/weight bearing
What is jumper’s knee?
- patellar tendinopathy
- chronic pain in patellar ligament/tendon
Why does jumpers knee occur?
- overuse & wear
- Extrinsic: training intensity, playing surface/footwear
- Intrinsic: strength, endurance, flexibility, skill level, BW + height, male
What is patellofemoral pain syndrome?
- pain behind patella & anterior to femur
- usually worse w/ squatting, stair climbing, prolonged sitting w/ knee flexed
What are some causes of patellofemoral pain syndrome?
- neurological, genetic, neuromuscular
Biomechanical
- stress intolerance of articular cartilage & subchondral bone
- abnormal tracking & alignment of patella in trochlear groove
How would you instruct someone to squat who had patellofemoral pain syndrome?
- restrict ROM on a squat
- don’t deep squat and keep knees behind toes (this shifts IMA of quads and increases IMA of hip extensors)
- don’t allow knees to collapse and don’t stress quads too much
What is the mechanism of injury for meniscal tears?
- forceful, axial rotation of femoral condyles over a flexed & weight bearing knee
- pinches and dislodges meniscus
What are potential consequences of a partial meniscectomy?
- less coverage & shock absorption for articular cartilage ALL leads to OA
What is the mechanism of injury for an ACL injury?
- non-contact
- strong quad contraction over slightly flexed knee
- valgus collapse
- excessive ER + planted foot
- knee IR + EXT + valgus
- hyperextension + planted foot
What are some related injuries to an ACL injury?
- cartilage degeneration
- menisci degeneration
- MCL tear/rupture
What is the terrible triad?
- MCL tear
- ACL tear
- Medial meniscus tear
Why are female athletes more likely to tear an ACL than male athletes?
- tend to land w/ knees in greater valgus alignment
- land with less trunk, hip, & knee flexion
- quad dominant landing
- pulls tibia anterior & strains ACL
How would you choose to strengthen the quads after an ACL surgery & why?
- close chained quad training (leg press, squats)
ACL strain greatest w/ isolated quad contraction in last 30-40 degrees of extension
- limit ROM and don’t do open-chain knee extension in early stages
What are the AAOS norms for knee flexion and extension?
Flex: 135
Ext: 10
