Knee Joint Flashcards
How many joints share the capsule at the knee joint?
2
What are the two articulations of the knee joint?
Femur with tibia = tibiofemoral
Femur with patella = patellofemoral
What is the largest sesamoid bone in the body?
Patella
Why is the knee a modified hinge joint?
Have rotation when flexed, unlike normal hinge joint which only flexes and extends
What movement is required to flex the knee?
Rotation
What is the range of movement of the knee joint?
Relatively large
What is a close packed position?
Articular surfaces meet each other to greatest extent
Ligaments tight
What is the close packed position of the knee?
Extension
What is the loose packed position of the knee?
Midway through flexion
Why is the stability of the knee joint not from the bones?
Mismatch of shapes of articular surfaces: rounded femoral condyle articulating with flat tibial plateau
What gives the knee joint its stability?
Strong ligaments reinforcing capsule
Muscles attaching at joint
What is the notch between the femoral condyles?
Intercondylar notch
What is the nick in the intercondylar notch for?
Indentation of anterior cruciate ligament
What can cause erosion of the anterior cruciate ligament?
Narrow intercondylar groove (nick in intercondylar notch)
Which femoral condyle is longer, and by how much?
Medial femoral condyle longer by 1 cm
Which femoral condyle is wider?
Lateral femoral condyle
What action is the position of the anterior cruciate ligament very important for?
Hyperextension at knee > stand upright
Which femoral condyle bears the most weight, and what proportion is it?
Medial femoral condyle bears 75% of weight
Which femoral condyle undergoes more osteoarthritic changes?
Medial femoral condyle
With a valgus deviation, what is the change in weight bearing at the knee?
Lateral femoral condyle bears more weight than normal
What covers the tibial plateau in the medial and lateral aspects?
Articular cartilage
What covers the margins of the tibial plateau?
Menisci
What are the menisci made of?
Fibrocartilage
What do the menisci in the knee joint do?
Support femoral condyles
From anterior to posterior, what attaches to the central, raised part of the tibial plateau?
Anterior horn of medial meniscus Anterior cruciate ligament medially, Anterior horn of lateral meniscus laterally Posterior horn of lateral meniscus Posterior horn of medial meniscus Posterior cruciate ligament
What is the femoral attachment of the anterior cruciate ligament?
Lateral aspect of lateral femoral condyle
What is the femoral attachment of the posterior cruciate ligament?
Medial femoral condyle
What is the shape of the cruciate ligaments from the front?
Cross
What 3 pairs of non-muscular structures support the capsule at the knee joint?
Anterior and posterior cruciate ligaments
Medial and collateral ligaments
Medial and lateral menisci
When are the structural supports at the knee especially susceptible to injury?
In flexion and rotation
What is the extent of the capsule in the knee?
Runs around knee
Surrounds patellofemoral joint
Passes behind femoral condyles and tibial plateau
What lines the capsule?
Synovial membrane
What is the extent of the synovial membrane at the knee?
Doesn’t line everything
Passes to sides of posterior cruciate ligament then passes around and in front of anterior cruciate ligament
What is the relationship of the cruciate ligaments with the capsule and the synovial membrane?
Intracapsular by extrasynovial
How do you tell the medial and lateral menisci apart?
Medial meniscus more open, with horns further apart
Lateral meniscus more circular, with horns closer together
Why is the anterior cruciate ligament associated with considerable bleeding when it tears, when it is relatively avascular?
Because of intimate association with synovial membrane
Blood mostly coming from tears to membrane
What is haemarthrosis?
Bleeding because of tear in synovial membrane
What is effusion?
Production of extra synovial fluid
What is the relationship between the capsule and the medial collateral ligament?
Medial collateral ligament essentially merges with medial aspect of capsule
What is the relationship between the capsule and the lateral collateral ligament?
Lateral collateral ligament somewhat detached from capsule
What reinforces the knee joint anteriorly?
Patellar tendon/ligament
Medial patellar retinaculum
From which muscles does the medial patellar retinaculum arise?
Vastus medialis
Vastus lateralis
What reinforces the knee joint laterally?
Popliteus
Biceps femoris
Iliotibial band
What reinforces the knee joint medially?
Pes anserius tendons
- Sartorius
- Gracilis
- Semitendinosus
What reinforces the knee joint posteriorly?
Oblique popliteal ligament
From what does the oblique popliteal ligament arise?
Semimembranosus
How does the lateral patellar retinaculum change the position of the patella?
Drags it laterally
Can the muscular reinforcements of the knee cover for damage to the cruciate ligaments?
Yes
What is the collective name for the muscular reinforcements of the knee?
Secondary restraints
How do you remember the muscle insertions of the pes anserinus from superior to inferior?
Say = sartorius Grace = gracilis Before = bursa Tea = semitendinosus
What does the anterior cruciate ligament do?
Primary stabiliser in the A-P direction
Limits forward displacment of tibia on femur
When is the anterior cruciate ligament taut?
Extension
Full flexion
What is the loose packed position of the anterior cruciate ligament?
Semi-flexion
What are the two bands of fibres in the anterior cruciate ligament?
Anteromedial - most taut in extension
Posterolateral - most taut in complete flexion
What is the role of the anterior cruciate ligament when it tightens in the last 15-20 degrees of extension?
Axis for rotation during terminal extension
What does the anterior cruciate ligament allow during extension?
Medial rotation on fixed tibia
Limits backwards movement of lateral condyle
What can a person with a tear in their anterior cruciate ligament not do?
Properly lock joint > unstable in full extension
What sound is often heard with an injury to the anterior cruciate ligament?
Pop sound
When does injury to the anterior cruciate ligament occur?
Lateral rotation
Involves extension on weight-bearing leg
How much thicker is the posterior cruciate ligament than the anterior cruciate ligament?
2x
What is a common variant that reinforces the posterior cruciate ligament?
Meniscofemoral ligaments
What does the posterior cruciate ligament do?
Limits posterior displacement of tibia in knee flexion
When is the posterior cruciate ligament prone to injury?
Fall on flexed knee
What is the course of the popliteus muscle?
Runs across back of joint
Passes under lateral collateral ligament
Attaches to outside of lateral femoral condyle
What does the popliteus do?
Rotates femur laterally on fixed tibia
What is the role of the popliteus in unlocking the knee joint?
Contraction allows knee joint to flex to do other activities
Describe the superficial part of the collateral ligament?
Long, flat band
What is the relationship of the medial collateral ligament and the capsule and medial meniscus?
Deep part blends with capsule and attaches to medial meniscus
When is the medial collateral ligament taut?
Extension
When is the medial collateral ligament slack?
Flexion
What does the medial collateral ligament do?
Resist valgus forces and lateral rotation of tibia
What does the medial collateral ligament do when the anterior cruciate ligament is damaged?
Secondary restrain - limits anterior displacement of tibia
What is the unhappy triad?
Injury to all
- Anterior cruciate ligament
- Medial collateral ligament
- Medial meniscus
What separates the lateral collateral ligament from the lateral meniscus?
Popliteus tendon
What does the lateral collateral ligament do?
Resist varus forces
Which collateral ligament is more often injured?
Medial collateral ligament
What are the attachments of the lateral collateral ligament?
Lateral femoral condyle
Fibula
What is the shape of the menisci in the knee?
Wedge shaped
What are the functions of the menisci in the knee?
Shock absorb
Weight distribution
Separates joint into 2 cavities
With which structure do the menisci move in rotation?
Femur
By how much do the menisci increase area of contact?
1/3
Are the menisci within the synovial cavity or extrasynovial?
Within synovial cavity, but only bony attachments have covring
Which meniscus is more often injured, and why?
Medial meniscus, because
- Longer
- Horns further apart
- Less mobile
What kind of injuries can occur to the medial meniscus?
Nipped
Torn
What does an injury to the medial meniscus contribute to?
Locked knee
What happens if the menisci are completely removed?
Increased incidence of osteoarthritis
What are the two zones of the menisci, as defined by their blood supply?
Outer 1/3 has blood supply = red zone
Inner 2/3 avascular = white zone
What is a bursa?
Sac with small amount of fluid in it
What can happen to bursa with irritation?
Fluid inside can increase
Where is the quadriceps/suprapatellar bursa?
In knee joint, deep to quadriceps muscle
What is the largest bursa in the body?
Quadriceps bursa
What is the superior extent of the suprapatellar bursa?
Hand’s breadth above tibiofemoral joint
Does the suprapatellar bursa communicate with the knee joint?
Yes
Where can an effusion at the knee joint expand into?
Suprapatellar bursa
How can the extent of the effusion into the suprapatellar bursa be estimated?
Pressing down on bursa to push fluid back into joint cavity
What is a baker’s cyst?
Bursa deep to popliteus becomes fibrous
Where are there bursae in the knee?
Wherever
- Ligaments attach
- Large tendon sliding over bone
Where is the prepatellar bursa?
Superficial to patella
Where are the superficial and deep infrapatellar bursae?
Inferior to patella
Which bursae are non-communicating with the knee joint?
Prepatellar
Superficial infrapatellar
Deep infrapatellar
Can non-communicating bursae still become irritated?
Yes
What is the relationship between the synovial membrane and bursae at the knee joint?
Lines communicating bursae
What part of the cruciate ligaments does the synovial membrane conver?
Front
What are plicae?
Fringes/folds of synovial membrane
Where are there plicae in the knee joint?
Medially and laterally
What is the relationship between the synovial membrane and infrapatellar fat pad?
Synovial membrane sits on top of infrapatellar fat pad
Where is the patellofemoral joint?
In front of femur
What is the surface of the femur that articulates with the patella called?
Patellar surface
Where does the quadriceps tendon attach?
Upper aspect of patella
How does the patella move across the femur?
Slides up and down and rotates to some extent in grooved part of femur
What is the quadriceps’ action on the patella?
Pulls patella up in extension
Pushes patella down in flexion
Where is the groove in which the patella moves across the femur?
Between lateral and medial femoral condyles
Which articular surface of the patella is larger: lateral or medial?
Lateral
What is a bipartite patella?
Two ossification centres of patella don’t merge
Looks like fracture on x-ray
What structures maintain the normal alignment of the patellofemoral joint?
Vastus medialis
Medial patellar retinaculum
Raised lip on lateral femoral condyle
In which direction does the patella rotate during extension?
Medially
What happens if the raised lip of the lateral femoral condyle is diminished in size/absent?
Tendency for patella to slide laterally
In which direction do the fibres of vastus medialis approach the patella?
Come towards medial aspect
Move almost horizontally - that’s why this section of muscle sometimes called vastus medialis oblique
What does the vastus medialis do in relation to the patella?
Helps keep it in place when moving from flexion to extension
What is the medial patellar retinaculum an extension of?
Vastus medialis to medial aspect of patella
Why is the medial patellar retinaculum a static structure?
Ligamentous
What acts upon the medial patellar retinaculum?
Vastus medialis
What happens if there is a deficiency in any of the structures that maintain the normal alignment of the patella?
Tendency for patella to slide in direction of femur
What is the angulation between the femur and tibia called?
Quadriceps (Q) angle
What tends to pull the patella laterally?
Quadriceps
What does abnormal tracking of the patella in its groove predispose you to?
Sublaxation
Dislocation
What is sublaxation?
Bone partially sliding across, but not completely dislocating
What part of the patella articulates with the femur if there is a mechanical problem of tracking of the patella in the femoral groove?
Medial part
Why doesn’t the medial part of the patella like to articulate?
Cartilage not very thick > wears away
What can a mechanical problem of tracking of the patella in the femoral groove cause?
Cartilage on medial aspect of patella wears away > contributes to arthritic changes at patellofemoral joint > chondromalacia patella
What is chondromalacia patella?
Softening/degeneration of cartilage at patellofemoral joint
