15. Anatomy of the knee

Question 1

Answer 1

Question 2

Functions of the knee

Answer 2

Question 3

Factors strengthening the joint

Answer 3

Several factors help improve stability and strength:

Bony factors

• Bony expansions
• Locking mechanism
• Femoral angle

Soft tissue factors

• Ligaments
• Menisci
• Muscles

Question 4

Bony expansions

Answer 4

Question 5

Locking mechanism

Answer 5

Reduces amount of energy required when extended

3 components:

1. Shape of femur
2. Rotation
3. Centre of gravity

Question 6

1. Shape of femur

Answer 6

Question 7

2. Rotation

Answer 7

Medial rotation of femur on tibia in extension

• Tightens ligaments of the knee

Question 8

3. Centre of gravity

Answer 8

Centre of gravity in front of knee

• Maintains extension

Question 9

Femoral angle

Answer 9

Question 10

Varus deformity (Genu varum)

Answer 10

Deformity in the angle between femur and tibia

Medial displacement of the tibia

• Common in children under 2, rickets

Pushes knees apart - ‘Bow-legged’ = Decrease in Q angle

Question 11

Valgus deformity

Answer 11

Lateral displacement of the tibia

• Common in children aged 2-4, rickets, arthritis

Brings knees together - ‘Knock-kneed’ = increase in Q angle

Question 12

Ligaments of the knee

Answer 12

Provide stability

Two groups of strong ligaments:

Extracapsular – outside capsule

• Medial collateral
• Lateral collateral

Intracapsular – inside capsule

• Anterior cruciate
• Posterior cruciate

Question 13

Lateral/fibular collateral ligament

Answer 13

Question 14

Medial/tibial collateral ligament

Answer 14

Question 15

Intracapsular ligaments

Answer 15

Question 16

Function of cruciate ligament

Answer 16

Anterior cruciate

• Prevents anterior displacement of tibia on femur

Posterior cruciate

• Prevents posterior displacement of tibia on femur

Maintain femur against tibia

• Always one ligament tense

Question 17

Cruciate ligaments

Answer 17

Question 18

Anterior cruciate ligament

Answer 18

Weaker - can become injured

• Common sports injury
• Caused by sharp twisting of knee
• Immediate decreased range of movement

Lachman test (variation of Drawer test):

• Patient in supine position with knee bent 20-300 of flexion
• Move tibia anteriorly and posteriorly while maintaining position of femur
• Laxity during this manoeuvre indicates anterior cruciate ligament injury

Question 19

Posterior cruciate ligament

Answer 19

Stronger - Rarely injured

• Principle stabilizer when knee flexed

(Especially when walking down hill)

Question 20

Menisci of joint

Answer 20

Crescent-shaped plates of fibrocartilage

• Deepen the articulating surfaces/stability
• Shock absorbers
• Provides smooth viscous film for joint

Question 21

Menisci attachments

Answer 21

Horns of menisci attached to intercondylar area of tibia

Mobile - Accommodates rolling of femoral condyles

Medial meniscus less mobile

• Attached to medial collateral ligament

Question 22

Unhappy triad

Answer 22

Twisting on a flexed knee/blow to lateral side

Contact sports (rugby tackle)

Locking of the knee

Rupture:

• Anterior cruciate ligament
• Medial collateral ligament
• Medial meniscus (attached to MCL)

Poor blood supply to intracapsular structures

Doesn’t repair easily

Question 23

Muscles acting on knee joint

Answer 23

Knee reinforced by tendons from surrounding muscles and iliotibial tract

Iliotibial tract

• Reinforces joint capsule
• Stabilizes extended knee
• (gluteus maximus, tensor fascia lata)

Question 24

Extensors of leg

Answer 24

Quadriceps extends leg

Major stabilizing muscle of the knee

4 heads:

• Rectus femoris
• Vastus lateralis
• Vastus intermedialis
• Vastus medialis

Question 25

Quadriceps femori

Answer 25

Question 26

Extensor mechanism

Answer 26

Question 27

Extensor mechanism injury

Answer 27

Rupture of quadriceps tendon or patellar ligament Fracture of the 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

Question 28

Flexors of leg

Answer 28

Hamstrings and gastrocnemius flex leg Hamstrings actually three muscles: * Biceps femoris * Semimembranosus * Semitendinosus Also medially and laterally rotates leg when knee flexed And extends thigh

Question 29

Hamstrings

Answer 29

Question 30

Unlocking of extended leg

Answer 30

Popliteus unlocks knee joint * Laterally rotates femur on tibia when foot is on ground

Question 31

Synovial membrane

Answer 31

From margins of articular surfaces of femur to tibia Attached to patella Extends superiorly behind quadriceps tendon Cuffs anterior surface of cruciate ligaments

Question 32

Bursae

Answer 32

Synovial fluid filled sac lined by synovial membrane * Protection * Reduce friction Many bursae associated with the knee occur at tendon insertions

Question 33

Posteriolateral and posteriomedial aspects of knee

Answer 33

Question 34

Bursitis

Answer 34

Inflammation of bursae * Due to repetitive movements or direct pressure Prepatellar bursitis (‘housemaid’s knee’) * Seen in carpet fitters Leaning forward on the knees brings the prepatellar bursa in contact with floor

Question 35

Infrapatellar bursitis

Answer 35

(clergyman’s knee’) After prolonged periods of prayer clergymen sat back on their heels bringing infrapatellar bursa in contact with floor

Question 36

Popliteal/Baker's cyst

Answer 36

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

Question 37

Vascular supply

Answer 37

Anastomosis around knee - Femoral artery - Popliteal artery Limited blood supply to intracapsular structures - Poor repair following injury