knee Flashcards
Movement between 2 objects can be categorized into which 3 groups? Which 2 are seen in the knee joint?
Slide/glide: single point on one surface contacts multiple points on another
Roll/rock: multiple points on one surface contact multiple points on another
Spin: single point on one surface rotates on a single point on another
At knee: slide and roll
What are the 3 degrees of freedom at the knee joint?
Abduction/adduction
Flexion/extension
Internal/external rotation
True or false: the knee is a hinge joint
False - there are no hinge joints in the body. The axis of rotation changes as the joint moves
Which 2 joints are contained within the knee complex?
Tibiofemoral
Patellofemoral
The differences in shape and orientation of the femoral condyles are important for what mechanism?
Screw home
Which is larger: the articulating surface of the medial or lateral condyle?
Medial (50% larger)
The articular cartilage is thicker on the (femur/tibia)
Tibia (x3)
What structure greatly enhances the articular congruence of between the spherical femoral condyles and the flat tibial plateaus?
Menisci
Which meniscus is C shaped? Which is more circular?
C: medial
Circular: lateral
Name the 5 structures attached to the medial meniscus
ACL MCL Semimembranosus tendon Coronary lig Transverse lig
Name the 4 structures attached to the lateral meniscus
Popliteal tendon PCL Transverse lig Coronary lig NOT LCL (outside jt capsule)
What is the normal tibiofemoral angle?
185-190deg
How do you measure the mechanical axis of the lower limb? Why is this useful? What is a normal measurement?
From centre of head of femur to centre of talus
Shows weight distribution over knee (should pass through centre of knee)
Normal: 3deg from vertical
What is the threshold measurement for genu valgum? For genu varum?
Valgum: >195deg
Varum: <180deg
What changes are typically seen in the knee and foot joints in individuals with coxa vara?
Genu valgum
Supination of subtalar joint and transverse tarsal joint
In which direction is the knee most unstable? What limits this motion?
Flexion
Joint capsule + associated ligaments
In which knee position is the MCL most important in resisting valgus stress: flexion or extension?
Flexion (because other structures are lax in this position)
Other than resisting valgus stress, what other 2 jobs does the MCL have in limiting knee motion?
Limits lateral rotation of tibia
Limits anterior displacement of tibia (espec when ACL absent/ruptured)
Other than resisting varus stress, what other 2 jobs does the LCL have in limiting knee motion?
Limits lateral rotation of tibia (espec at 35deg of flexion)
Limits posterior displacement of tibia
True or false: the IT band is taut in knee extension and slack in knee flexion
False - consistently taut regardless of hip and knee position
Which knee ligament does the IT band assist? How?
ACL
Forms a sling behind lateral femoral condyle with the biceps femoris and vastus lateralus to hold the femur anteriorly
What kind of collagen makes up the ACL and PCL?
Composed of Type I Collagen, separated by Type III collagen fibrils
In which knee position is the ACL lax?
30degrees of flexion
Other than anterior translation, what motions does the ACL resist?
Medial rotation (ACL twists around PCL) Lateral rotation (ACL is stretched over lateral femoral condyle)
In which knee position is the PCL most lax?
75-90deg flexion
The oblique popliteal ligament is created by the tendinous expansion of which muscle?
Semimembranosus
Which 2 ligaments reinforce the posterior aspect of the knee joint capsule? What direction of force does each resist?
Oblique popliteal ligament: valgus stress
Arcuate popliteal ligament: varus stress
Both resist hyperextension
When the knee is in extension, which direction does the synovial fluid go to? Why?
Anterior - posterior capsule and ligaments are taught which compresses the gastroc and sub-popliteal bursae, shifting the fluid anterior
In which position is the suprapatellar bursa the least compressed? Why?
In extension, the suprapatellar bursa is compressed by posterior structures moving the fluid anterior
In flexion, the suprapatellar bursa is compressed by the tension in the anterior structures, shifting the fluid posterior
During a semi-flexed position, the synovial fluid is under the least amount of tension
Which 2 knee bursae are located within the capsule? Which 3 are outside the knee capsule?
Inside: gastroc and suprapatellar
Outside: pre-patellar, subcutaneous infrapatellar, deep infrapatellar
How is the axis of flexion/extension oriented in the knee? What effect does this have on the alignment of the femur and tibia?
Lower on medial side (oblique angle)
Causes tibia to sit medial to the femur during flexion
Passive knee flexion is _____ when the hip is flexed and _____ when the knee is extended
130-140deg
120deg
Match the ADL with the amount of knee flexion required:
- Normal gait
- Climbing stairs
- Sitting in chair
a. 80deg
b. 90 deg
c. 60deg
1 - c
2 - a
3 - b
What is the close-packed position of the knee?
Full extension
In which knee position is there the greatest tibial rotation range?
90degrees flexion
What is the total possible tibial rotation? How much is lateral rotation and how much is medial rotation?
60-70deg total
Lat: 0-40deg
Med: 0-30deg
In open-chain tibial rotation, which tibial condyle moves most: medial or lateral?
Lateral (posteriorly for lateral rotation, anteriorly for medial rotation)
Medial acts as pivot point
How can you isolate soleus from gastroc in terms of plantar flexion?
Stand on toes and slightly flex knee (causes active insufficiency)
What is one of the key functions of gastrocnemius during gait?
Prevents knee joint hyperextension
In which position are the hamstrings actively insufficienct?
Hip extension
Knee flexion
Dr. Ross does not believe that popliteus is actually for unlocking the knee joint. What function does he believe it serves?
Moving the meniscus out of the way during unlocking.
What 3 functions do the quads serve during the gait cycle?
Decelerate flexion of knee during early swing
Straighten knee during end of swing
Keep knee from flexing when ground rxn force is posterior to the knee
]What is the screw home mechanism of the knee? How does it work?
Helps keep knee stable by causing joint surfaces to be more tightly packed as cruciate ligs wind around each other
Occurs when tibia is externally rotated relative to femur
At what point in gait does the screw home mechanism unlock? What does the tibia do to facilitate this?
20 degrees of flexion
Tibia rotates internally
The pressure on the patellofemoral joint is determined through the combined forces of which 4 structures?
Quad tendon
Patellar lig
Medial and lateral retinacula
IT band
In the patellofemoral joint, increasing flexion causes the weight-bearing portion to shift from the _______ pole to the _______ pole
Inferior
Superior
A patient reports that they have patellofemoral pain only on full extension of the knee. Which part of the patellofemoral joint is most likely affected?
Odd facet
A patient reports that they have patellofemoral pain only on full flexion of the knee. Which part of the patellofemoral joint is most likely affected?
Superior pole
Why is it important to avoiding having a bike seat too low?
Knee is in more flexed position. Decreases moment arm, requiring greater quad strength and increasing patellar compression
What important role do the superior and inferior tibiofibular joints play in ankle biomechanics?
Allows ankle mortise joint to be adjustable. Important because the anterior aspect of the talus is wider than the posterior aspect. Allows for full plantar and dorsiflexion without compromising joint stability.
