12. Functional Anatomy Of The Knee

Question 1

What type of movement does the knee joint allow for?

Answer 1

The knee joint is a hinge-type synovial joint, which mainly allows for flexion and extension with a small degree of medial and lateral rotation

Question 2

Which bones does the knee have articulations with?

Answer 2

articulations between the patella, femur and tibia.

Note, the fibula does not form part of the knee joint

Question 3

What are the 2 articulations that the knee joint consist of?

Answer 3

1) tibiofemoral - the medial and lateral condyles of the femur articulate with the medial and lateral tibial condyles
2) patellofemoral - the patella articulates with the femur as the trochlear (patellofemoral) groove

both enclosed within a single joint cavity

Question 4

Which joint of the knee is the weight bearing one?

Answer 4

The tibiofemoral joint

Question 5

What type of cartilage are the articulations of the knee joint lined with?

Answer 5

Hyaline cartilage

Question 6

What features of the patella increase the efficiency of the quadriceps femoris muscle?

Answer 6

• the patella allows the tendon of the quadriceps femoris (the main extensor muscle group of the knee) to be
inserted directly over the knee, increasing the efficiency of the muscle.
• As the patella resides within the quadriceps femoris tendon, it provides a fulcrum to increase the power of knee extension.
• It also reduces the frictional forces placed on femoral condyles by the contracting quadriceps tendon.
• Finally, it provides some protection from physical trauma for the anterior knee.

Question 7

How is the knee joint supplied with blood?

Answer 7

Through the genicular anastomoses around the knee, which are supplied by the genicular branches of the femoral and popliteal arteries

Question 8

What happens if the popliteal artery is gradually occluded by atheroma?

Answer 8

The genicular anastomoses can dilate to maintain the blood supply to the leg

Question 9

What nerves supply the knee joint?

Answer 9

• according to Hilton’s law, the nerves which supply the muscles which cross the joint supply the joint too: femoral, tibial, and common peroneal (common fibular) nerves

Question 10

How is the knee joint stabilised?

Answer 10

The knee joint is inherently unstable. To improve stability, the tibial articular surface is deepened by the menisci and the joint is supported by the joint capsule, ligaments and the surrounding musculature.

Question 11

What are the menisci of the knee? Where do they attach?

Answer 11

• medial and lateral
• fibrocartilaginous
• crescent shaped, thicker peripherally than centrally
• attach at both ends to the intercondylar area of the tibia

Question 12

What are the functions of the medial and lateral menisci of the knee joint

Answer 12

• to deepen the articular surface of the tibia to stabilise the joint
• to act as shock absorbers by increasing SA to further dissipate forces

Question 13

Where is the medial meniscus attached?

Answer 13

• Medially to the intercondylar attachments
• Peripherally to the medial collateral ligament and the joint capsule
• Therefore damage to the medial collateral ligament can result in a medial menisci last tear
• Peripheral rim attached loosely to tibia and to joint capsule by coronary ligaments

Question 14

Where is the lateral meniscus attached?

Answer 14

Smaller than the medial meniscus and isn’t attached to the lateral (fibular) collateral ligament, so it is fairly mobile

Question 15

How are the menisci connected anteriorly?

Answer 15

By the transverse ligament of the knee

Question 16

What does the posterior meniscofemoral ligament do?

Answer 16

Helps stabilise the posterior horn of the lateral meniscus by attaching it to the medial femoral condyle

Question 17

How are the menisci supplied with blood?

Answer 17

• From the periphery
• blood flow decreases with age and the medial meniscus is avascular by adulthood, leading to impaired healing after trauma

Question 18

How can the major ligaments in the knee joint be divided?

Answer 18

• Intracapsular ligaments: cruciate ligaments
• Ligaments that strengthen the capsule: oblique popliteal ligament
• Extracapsular ligaments: collateral ligaments, patellar ligament

Question 19

What do the cruciate ligaments do?

Answer 19

Connect the femur and tibia.

In doing so, they cross each other, hence the term ‘cruciate’ (Latin = like a cross).

Question 20

How does the anterior cruciate ligament attach?

Answer 20

the anterior CL attaches proximally to the posterolateral aspect of the femoral intercondylar fossa and passes distally and anteromedially to attach to the anterior aspect of the intercondylar eminence of the tibia, where it is also adherent to the medial meniscus

Question 21

What does the ACL do?

Answer 21

Resists anterior translation (movement) and medial rotation of the tibia in relation to the femur

Weaker of the two

Question 22

How does the posterior cruciate ligament attach?

Answer 22

• Attaches proximally to the medial border and roof of the intercondylar fossa
• Passes distally and posterolaterally to attach to the posterior intercondylar area of the tibia

Question 23

What does the PCL do?

Answer 23

• main stabiliser of the weight-bearing flexed knee (stronger of the two)
• prevents the femur from sliding off the anterior edge of the tibia e.g. when walking down stairs/ slope
• prevents posterior dislocation of the tibia on the femur

Question 24

Where does the joint capsule surround? Why is this good?

Answer 24

• The sides and posterior aspect of the knee joint but is deficient anteriorly
• This deficiency allows the synovial membrane to extend up beneath the patella to form the suprapatellar bursa

Question 25

What is a good way of remembering The orientation of the cruciate ligaments?

Answer 25

• Consider the anterior cruciate ligament from proximal to distal using the phrase “Hands in pockets”. Orientate your hands as if they are going into your pockets.
• Or consider both cruciate ligaments from distal to proximal, using the mnemonic:
PAMs APpLes:
Posterior passes Anterior inserts Medially
Anterior passes Posterior inserts Laterally

Question 26

How is the joint capsule strengthened?

Answer 26

• laterally and me daily by the inferior fibres of the vastus lateralis and medialis muscles respectively
• strengthened posteriorly by the oblique popliteal ligament: a continuation of some of the fibres from semimembranous tendon in a superolateral direction from its main insertion on the medial tibial condyle, posteriorly across the back of the knee to the lateral femoral condyle

Question 27

Where is the patellar ligament?

Answer 27

Continuation of the quadriceps femoris tendon distal to the patella.
Inserts onto the tibial tuberosity

Question 28

What do the medial and collateral ligaments do?

Answer 28

Strap like ligaments that act to stabilise the hinge motion of the knee, preventing excess medial or lateral angulation of the tibia on the femur

Question 29

Describe the medial collateral ligament

Answer 29

• Wide, flat
• Weaker than the lateral collateral ligament so excess lateral displacement of the tibia may cause it to tear, and in turn the medial meniscus to tear

Question 30

Where does the medial collateral ligament attach?

Answer 30

Proximally, it attaches to the medial epicondyle of the femur, distally it attaches to the medial condyle of the tibia.

Also, Attaches to the medial meniscus at its midpoint

Question 31

What does the medial collateral ligament do?

Answer 31

Resists valgus (lateral) angulation of the tibia on the femur 
(Resists valgus forces on the tibia (vaLgus = Lateral) )

Question 32

What does the lateral collateral ligament do?

Answer 32

Resists varus (medial) angulation of the tibia on the femur

Resists varus force on the tibia (varus = medial)

Question 33

Describe the lateral collateral ligament

Answer 33

• thinner and rounder than the medial collateral ligament
• Although weak in isolation, works as part of the
‘posterolateral corner’ together with the arcuate ligament and popliteus tendon, so overall is strong
• reinforced by the iliotibial tract

Question 34

Where does the lateral collateral ligament attach?

Answer 34

It attaches proximally to the lateral epicondyle of the

femur; distally it attaches to a depression on the lateral surface of the fibular head

Question 35

What is a bursa?

Answer 35

• small sac lined by synovial membrane
• contains a thin layer of synovial fluid
• can either by communicating or non-communicating with the joint cavity

Question 36

What do bursae in the knee joint do?

Answer 36

• provide a cushion between the bones and tendons/ muscles surrounding the joint
• helps reduce the friction and allows free movement

Question 37

How many bursae are in the knee joint?

Answer 37

6

Question 38

What are the 6 bursae of the knee joint?

Answer 38

1) suprapatellar: extension of the synovial cavity of the knee, located between the quadriceps femoris muscle and the femur
2) prepatellar: between the anterior surface of the patella and the skin
3) superficial/ subcutaneous infrapatellar: between the patellar ligament and the skin
4) deep infrapatellar: between the tibia and patellar ligament
5) semimembranous: posterior to knee joint, between the semimembranous muscle and the medial head of the gastrocnemius
6) subsartoiral: between the common insertion of the pes anserinus tendons (sartorius, gracilis, semitendinous) and the medial tibial condyle

Question 39

What movement does the knee joint allow?

Answer 39

• extension: produced by quadriceps femoris, (rectus femoris, vastus medialis, vastus lateralis, vastus intermedius) which inserts into the tibial tuberosity via the patellar ligament
• flexion: produced by the hamstrings (biceps femoris, semimembranous, semitendinous), assisted by gracilis, sartorius, popliteus, plantaris and gastrocnemius
• lateral rotation: only possible in a flexed knee - produced by biceps femoris
• medial rotation: only possible in a flexed knee - produced by semi membranous, semitendinous, gracilis, sartorius, popliteus

Question 40

How and when does the knee passively lock?

Answer 40

• when the knee is fully extended with the foot on the ground
• there is five degrees of medial rotation of the femoral condyles on the tibial plateau (so it takes less effort to stand)
• cruciate ligaments tighten
• lower limb becomes solid column to bear weight
• thigh and leg relax briefly without making the knee joint become unstable

Question 41

How can the knee be unlocked from a passive lock?

Answer 41

• the popliteus contracts, rotating the femur laterally by five degrees on the tibial plateau so flexion of the knee can occur

Question 42

What is the important role of muscles surrounding the knee?

Answer 42

The muscles around the knee play an important role in stabilising the knee joint.
The most important muscle group in this regard is the quadriceps femoris, especially the inferior fibres of vastus medialis, which are known as the vastus medialis obliquus (VMO; also called the obliquus genus). These fibres contract to resist lateral displacement of the patella out of the trochlear groove

Question 43

When extending the knee, why does the patella naturally try to be displaced laterally?

Answer 43

Due to the angle between the line of pull of the quadriceps muscle and the patellar ligament (Q angle)

Question 44

How can you avoid the patella naturally try to be displaced laterally when extending the knee?

Answer 44

Avoided by:
• the deep trochlear (patellofemoral) groove, which has a more prominent lateral femoral condyle anteriorly
• the fibres of the vastus medialis obliquus, which are inserted more distally into the patella and more horizontally than those of vastus lateralis. Contraction of these fibres resists the lateral displacement of the patella
• the iliotibial tract stabilises the lateral knee joint and popliteus, the hamstrings and gastrocnemius all help stabilise the posterior aspect of the joint