76 - Knee Joint Flashcards
Joints within knee joint capsule
Femur with tibia (tibiofemoral)
Femur with patella (patellofemoral)
Type of joint that knee joint is
Modified hinge joint (rotation occurs during flexion)
When is knee most stable?
In extension.
Relative sizes of tibial and femoral condyles
Medial condyles are longer than lateral, in antero-posterior direction.
Medial femoral condyle also extends further medially (upwards)
Part of knee that bears the most weight
Medial femoral condyle
Name for lateral displacement of bones of the leg, relative to tibia
Genu valgum (knock-kneed)
Name for medial displacement of bones of the leg, relative to tibia
genu varum (bow-legged)
Inter-condylar notch contents
Anterior cruciate ligament
Articular surfaces on tibial plateau
Almost flat, two articular surfaces.
Two groups of structures attaching to the tibial plateau
Anterior and posterior cruciate ligaments Meniscal attachments (four of these, lateral and medial)
What attaches to the meniscal attachments of the tibial plateau?
Medial and lateral menisces of the tibial
Arrangement of attachments of horns of medial and lateral menisci to tibial plateau
Medial attach far apart.
Lateral attach close together
Supports of knee joint
1-4
1) Capsule reinforced by muscle
2) Cruciate ligaments (anterior, posterior)
3) Collateral ligaments (medial, lateral)
4) Menisci (medial, lateral)
When is the knee most susceptible to injury?
When flexed
Attachment of capsult of knee joint
Around articular margins
Incorporates patellofemoral joint and intracapsular structures (EG anterior, posterior cruciate ligaments, menisci)
Location of synovial membrane, relative to cruciate ligaments.
Cruciate ligaments develop posterior to knee, push into space between articular surfaces during development, pushing synovial membrane away.
Cruciate ligaments are extrasynovial
Are menisci intra- or extra-synovial?
Intrasynovial, but not lined by synovial membrane
Capsular reinforcements of the knee joint 1 2 3 4
Anteriorly - patellar tendon + retinacular fibres
Lateral - popliteus, biceps femoris, iliotibial tract
Medial – ‘pes anserinus’ tendons
Posterior – (oblique popliteal ligament - from semimembranosus muscle)
Muscle reinforcing knee laterally
Popliteus muscle
Pes anserinus
‘Goose’s foot’
Muscle insertions reinforcing medial knee joint
Sartorius, gracilis, bursa, semitendinous muscles
Attachments of PCL
Attaches to posterior tibia, attaches to medial femur
Attachments of ACL
Attaches to anterior tibia, passes to lateral femur
Ligament that can compensate for a weaker PCL
Meniscofemoral ligament
Primary role of ACL
Prevents tibia being displaced anteriorly, relative to femur
When is ACL taut?
In extension, but also full flexion
Composition of ACL
Two fibres: anteromedial and posterolateral
Other role of ACL
Tightens in last 15-20 degrees of extension, acts as an axis for rotation (allows medial rotation on weight-bearing tibia).
When does ACL injury occur?
Rotation in lateral direction of weight-bearing knee
Sites for taking tendons for allografts for ACL injuries
Patellar tendon, pes anserinus
Thickness of PCL
About 2x as thick as ACL
What reinforces PCL?
Meniscofemoral rings
Primary role of PCL
Limits posterior displacement of tibia in knee flexion
When is PCL prone to injury?
Falling on flexed knee.
Bumper bar impact (being reversed into by a car)
Muscle required for unlocking of knee joint (from extension)
Popliteus muscle needs to contract
Role of popliteus
Rotates femur laterally on fixed tibia.
Unlocks knee joint (locking in extension)
Role of medial collateral ligament
Resists valgus (abduction) forces & lateral rotation of tibia - because of alignment (not vertical but A-P) limits anterior displacement of tibia when ACL damaged (2nd restraint)
Parts of medial collateral ligament
1
2
3
- long, flat superficial part
- deep part blends with capsule & attaches to medial meniscus
- taut in extension, slack in flexion
‘Unhappy triad’
ACL, medial collateral ligament and medial meniscus often injured together
Lateral collateral ligament shape
Round cord.
Role of lateral collateral ligament
Resists adduction (varus) forces
How does lateral collateral ligament join knee?
Separated from lateral meniscus by popliteus tendon
Is the lateral or medial collateral ligament more-commonly injured?
Medial.
Roles of menisci
1
2
3
Shock absorb
Weight distribution
Separates joint into two cavities
Increase articular surface by ~1/3
Movements of menisci
Move with femur in rotation
Location of menisci
Within synovial cavity, only bony attachments have covering.
Shape of menisci
Wedge-shaped
Meniscus which bears more weight
Lateral (covers more articular surface
Attachments of lateral meniscus
Attachment to PCL (via meniscofemoral ligaments), not lateral collateral ligament
When is the lateral meniscus in danger of compression?
Knee flexion (EG squatting). Can lead to posterior meniscal tears
Meniscal injury that is more common
Medial meniscal injury
Why is medial meniscus more likely to be injured?
1
2
3
It is longer
Horns are further apart (so meniscus is less capable of moving than lateral)
It is less mobile (because of attachment of deep fibres of medial collateral ligament)
Effect of meniscal injury
Can contribute to locked knee (can’t fully extend)
Moderately common anomaly of the patella
Bipartite patella.
Benign
Largest bursa of the knee
Suprapatellar bursa.
About a hand’s breadth above joint line of knee
Suprapatellar bursa
Communicates with knee joint cavity.
Largest bursa of the knee.
Projects superiorly to knee.
Relative sizes of femoral articular surfaces for patella
Lateral articular surface is larger than medial.
Gender in which patella is more likely to be dragged laterally
Females (because of greater angle between femur and tibia/fibula)
Structures maintaining normal alignment of patellofemoral joint
1
2
3
1) Strong vastus medialis muscle (active stabiliser)
2) Medial patellar retinaculum
3) Raised lip of lateral femoral condyle
Bursa of the knee that projects posteriorly
Popliteus or semimembranous bursa.
Commonly communicates with suprapatellar bursa (and therefore with joint cavity)
Effect of repeated flexion of knee on bursae
Can result in thickening of popliteus bursa, leading to ‘Baker’s cyst’.
Non-communicating bursae of knee
1
2
3
Prepatellar
Superficial infrapatellar
Deep infrapatellar
All protect tendons of knee joint
Location of fat pad in knee
Infrapatellar fat pad lies external to synovial membrane.
Inferior to patella.
Patello-femoral joint
Within knee joint capsule.
Articulation between patella and patellar surface of the femur
Why should knees be mobilised quickly after injury and repair?
Vastus medialis stabilises patella, and is vulnerable to atrophy if kept immobile, which increases risk of patellar subluxation
Name for mechanical problem of tracking of patella in femoral groove
Chondromalacia patella (leads to degeneration of cartilage)
