Anatomy of the knee Flashcards
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
What is the function of the patella?
- Protects quadriceps tendon from stresses during locomotion
- Provides a smooth oval facet for articulation with femur
Which tendon lies superior to the patellar?
Which ligament lies inferior to the patellar?
Which structures lie medially and laterally to the patellar?
FORM EXTENSOR MECHANISM
- Quadriceps tendon
- Patella ligament
- Medial patellar retinaculum which helps stabilise the patella
- Lateral patellar retinaculum
What are the main injuries to the extensor mechanism that occur?
- Rupture of quadriceps tendon or patellar ligament
- Fracture of patella: due to fall or blow to knee
RESULTS IN LOSS OF ACTIVE EXTENSION
- Dislocation of patella common- due to sudden twisting/jumping or ligamentous laxity
What are the flexors of the leg?
HAMSTRINGS
- Biceps femoris, semitendinosus, semimembranosus
- Also medially and laterally rotate leg when knee flexed
- Extend thigh
GASTROCNEMIUS
What is the function of semimembranosus?
Reinforces joint capsule
Which muscle is involved in unlocking knee?
What is its origin, insertion and function?
Popliteus unlocks the knee
- it passes through joint capsule
Origin: lateral condyle of femur
Insertion: posterior tibia
Laterally rotates femur on tibia when foot is on ground
Outline the extent of the synovial membrane
- From margins of articular surfaces of femur to tibia
- Attached to patellar
- Extends superiorly behind quadriceps tendons
- Cuffs anterior surface of cruciate ligaments
What is the function of the infrapatellar fat pad?
Where is it found?
- Seperates synovial membrane from patellar ligament
- Behind patellar ligament
What are bursae?
Function?
What are the three main bursae associated with the knee joint?
- Synovial fluid filled sac lined by synovial membrane
- Protection, reduce friction
- Suprapatellar bursa- continuous with synovial membrane
- Prepatellar bursa
- Infrapatellar bursa
Where do other bursa associated with knee occur?
- Occur at tendon insertions
Iliotibial tract, biceps femoris, semimembranosus, semitendinousis, gracilis, sartorius
What is bursitis?
What is housemaids knee?
Inflammation of bursae due to repetitive movements or direct pressure
Prepatellar bursitis seen in carpet fitters
- leaning forward on the knees brings the prepatellar bursa in contact with floor
What is clergyman’s knee?
- Infrapatellar bursitis
- After prolonged periods of prayer clergyman sat back on their heels bringing infrapatellar bursa in contact with floor
What is a bakers cyst?
Amongst whom is it common?
Presentation?
Treatment?
Abnormal fluid filled sacs in popliteal fossa
- Due to herniation of synovial membrane/bursa
Common in patients with chronic
inflammatory joint disease (e.g. arthritis)
- Presents as swelling in the popliteal fossa
- Can affect joint movement
Treat by aspiration and cortisone injection
What is vascular supply to the knee?
- Anastomosis around knee between femoral and popliteal artery (genicular braches)
- Limited blood supply to intracapsular structures
