Anatomy of the knee Flashcards
(38 cards)
What kind of joint is the knee?
What bones form its articulation?
- Synovial bicondylar hinge jont
(articulation between distal femur and proximal tibia)
+ articulation between femur and patella (fibrous joint capsule formed by a network of tendons and ligaments)
What are the functions of the knee
- weight bearing
- mobility (extension/flexion, some rotation when flexed)
**Incompatible functions –> frequent injury
State the bony and soft tissue factors which improve the stability and strength of the knee
BONY FACTORS
- Bony expansions, locking mechanism, femoral angle
SOFT TISSUE FACTORS
- ligaments, menisci, muscles
Name the bony expansions involved in the knee joint
FEMUR
- Epicondyles, condyles, intercondylar fossa (posterior)
TIBIA
- condyles (tibial plateau)
What is the first function of the locking mechanism?
How is it facilitated?
- Reduces amount of energy required when extended
- Facilitated by the shape of the femur. In flexion, femoral surfaces round, in extension, femoral surfaces flat
The locking mechanism also facilitates rotation and acts as centre of gravity. How so?
- Medial rotation of femur on tibia in extension tightens ligaments of the knee
- Places centre of gravity in front of knee which maintains extension
What is the femoral angle? When does it occur?
Adducted femur brings knee joint under pelvis which is critical for weight bearing
- Normal alignment of joint (mechanical axis): vertical line through centre of femoral head, centre of knee, centre of ankle
- As opposed to anatomical axis which forms a Q angle (approx 15 degrees)
Occurs during development
What is varus deformity (Genu varum)?
Effect on Q angle?
Who is commonly affected?
Consequence?
- Deformity in the angle between femur and tibia
- Medial displacement of tibia
- Pushes knees apart (bow legged)
- Decrease in Q angle
- Common in children<2, rickets
Increased stress at medial condyle –> joint degeneration
What is valgus deformity (Genu valgum)?
Effect on Q angle?
Who is commonly affected?
Consequence?
- Deformity in the angle between femur and tibia
- Lateral displacement of tibia
- Pushes knees together (knock kneed)
- Increase in Q angle
- Common in children aged 2-4, rickets, arthritis
Increased stress at lateral condyle –> joint degeneration
What is the function of the ligaments of the knee?
State the names of the extracapsular and intracapsular ligaments
Provide stability
Extracapsular:
- medial and lateral collateral
Intracapsular:
- anterior and posterior cruciate
Describe the lateral collateral ligament
Shape
Function
Between which bony features?
Pathology
- Strong round cord
- Prevents medial displacement of tibia
- From lateral epicondyle to fibular head. Space underneath
- Tear of LCL = varus deformity, less common
Describe the medial collateral ligament
Shape
Function
Between which bony features?
Pathology
- Broad flat ligament
- Prevents lateral displacement of tibia and reinforces joint capsule (via attachment to medial meniscus)
- Medial epicondyle and tibia
- Tear of MCL= valgus deformity
Where do the anterior and posterior cruciate ligaments lie?
- In intercondylar fossa of femur and intercondylar area of tibia
- Anterior: anterior relative to tibia
- posterior: relative to tibia
What is the function of the cruciate ligaments?
ACL- prevents anterior displacement of tibia on femur
PCL- prevents posterior displacement of tibia on femur
Together they maintain femur against tibia, always one ligament tense
Describe the trajectory of the cruciate ligaments
ACL- passes up, backwards and laterally
PCL- passes up, forwards and medially
In a flexed knee what does medial and lateral rotation do to the cruciate ligaments
Medial rotation tightens ligaments, limits rotation (10degrees)
Lateral rotation unwinds ligaments (approx 0 degrees)
Which cruciate ligament is most prone to injury? Why?
Which kinds of injuries cause this? Result
How can you test the integrity of the ligament
ANTERIOR because it is weaker
- Sports injury caused by sharp twisting of knee
- Immediate decreased range of movement
LACHMAN TEST
- Patient supine with knee bent to 2-30 degree flexion
- Move tibia anteriorly and posteriorly while maintaining position of femur
- Laxity during this manoeuvre indicates ACL injury
When might the PCL become injured?
Walking down hill
- Rarely injured as stronger
It is the principle stabiliser when knee is flexed
What are menisci?
What are their functions?
Describe the menisci of the knee joint
- Crescent shape plates of fibrocartilage
- Deepen the articulating surfaces for increased stability; shock absorbers; provide smooth viscous film for joint
- Lateral meniscus is smalled and more circular; larger medial meniscus. Surrounded by horns of menisci
What are the attachments of the menisci?
How does this affect mobility?
- Horns of menisci attaches to intercondylar area of tibia
- This accomodates rolling of femoral condyles
Medial meniscus less mobile as its attaches to MCL
The unhappy triad results in rupture of which structures? Why dont they repair easily?
How do they become ruptures?
- Medial meniscus
- MCL
- Anterior cruciate
Poor blood supply to intracapsular structures
Twisting on a flexed knee/blow to lateral side; contacts sports; locking of knee
What is the function of the iliotibial tract
- Reinforces joint capsule
- Stabilises extended knee (glut max, tensor fascia lata)
What are the muscles important in extension of the leg
Quadriceps
- Vastus medialis
- Vastus Intermedialis
- Vastus lateralis
- Rectus femoris
Major stabilizing muscle of knee
What is the functions of the oblique fibres of vastus medialis?
Prevents lateral tracking of patella
