Lecture 3: The Knee Joint Flashcards
What kind of joint is the knee joint?
Synovial hinge
Which three bones are involved in the knee joint?
- distal femur
- proximal tibia
- patella
What are the 3 articulations involved in the knee joint?
2 femorotibial
> medial and lateral
1 femoropatellar
What movements are possible at the knee joint?
- Flexion
- Extension
- Medial rotation of leg, knee joint flexed 90 degrees
- Lateral rotation of leg, knee joint flexed 90 degrees
What is ‘locking’ of the knee joint?
As joint approaches full extension, femur undergoes a few degrees of medial rotation on the tibia.
This is called ‘locking’ the knee
Very stable position therefore thigh muscles can relax
How is the knee ‘unlocked’?
The knee is ‘unlocked’ by the popliteus muscle which laterally rotates the femur.
What is the tibial plateau?
The surface of the tibia above the medial and lateral tibial condyles. (see knee lecture).
Why is the femorotibial joint incongruant?
There is a poor fit between the rounded ends of the femoral condyles and and the tibial plateau.
When does the joint have most congruence?
In extension
What deepens the tibial plateau?
The menisci
What are the menisci?
- 2 c-shaped wedges of fibrocartilage
- Thicker at external margins
What are the functions of the menisci?
- Increase joint congruency
- Distribute weight evenly
- Shock absorption
- Assist in locking mechanism
What are the attachments of the menisci?
- External edges attach to the fibrous capsule of the joint
- Medial meniscus is firmly attached to the tibial collateral ligament
What are the causes of menisceal tears?
- Can be due to a sports injury or degenerative changes
What ligaments lie within the joint?
- intra-articular
- the anterior & posterior cruciate ligaments (inside the joint capsule)
What ligaments lie outside the joint?
- extra-articular
- the fibular & tibial collateral ligaments
What is the basic structure of the cruciate ligaments?
Cross each other obliquely in the centre of the knee
What is the structure of the posterior cruciate ligament?
The posterior cruciate ligament attaches to the posterior intercondylar region of the tibia and travels supero-anteriorly to insert onto the medial femoral condyle.
What is the structure of the anterior cruciate ligament?
The anterior cruciate ligament attaches to the anterior intercondylar region of the tibia and travels supero-posteriorly to attach to the lateral femoral condyle.
Which of the cruciate ligaments is the strongest?
PCL is stronger than the ACL
What is the function of the PCL?
Prevents posterior displacement of the tibia on the femur
Prevents hyperflexion
Main stabiliser of the flexed knee when weight bearing e.g. walking down hill
How might PCL injury occur?
Can be damaged when landing on the tibial tuberosity with the knee flexed.
What is the function of the ACL?
Prevents anterior displacement of the tibia on the femur
Prevents hyperextension
How might ACL injury occur?
Occurs when knee is hyperextended or force is applied anteriorly.
Where is the tibial (medial) collateral ligament?
Flat band attached to medial meniscus
What is the function of the medial ligament?
Prevents abduction of the leg at the knee.
Where is the fibular (lateral) collateral ligament?
Cord-like band NOT attached to lateral meniscus.
What is the function of the fibular collateral ligament?
Prevents adduction of the leg at the knee.
What is the function of both collateral ligaments together?
Prevent rotation during extension of the knee contributing to stability while standing.
What is the ‘unhappy triad’?
- Caused by excessive lateral twisting of the flexed knee or blow to lateral side of extended knee
- Tears the tibial collateral ligament which is attached the medial meniscus, which also then tears
- ACL may then also tear – as it is taut during flexion
Common when flexed knees are twisted
Which muscles are the main stabilisers of the knee?
- Quadriceps
- Hamstrings (posterior thigh)
- Sartorius
- Gracilis
- Iliotibial tract
What is the Q angle?
The angle between the femur on the tibia.
i.e. the femur sits obliquely on the knee joint.
Why do women have a larger Q angle?
They have a wider pelvis - femur is more oblique than in males.
What is a larger Q angle associated with?
Stronger quad contraction and possible dislocation.
What is genu varum?
Bow leg - tibia adducted with respect to femur (i.e. knees bow outwards)
What genu valgum?
Knock knee - tibia abducted with respect to femur (i.e. knees knock together)
