Lecture 9 - Biomechanics of the Knee (part 2)

Question 1

What are the main knee extensors?

Answer 1

Quadriceps femoris:
- rectus femoris
- vastus intermedius
- vastus lateralis
- vastus medialis

Question 2

What kind of muscle is the rectus femoris?

Answer 2

multi-joint muscle

Question 3

What effects of weakness does the rectus femoris have?

Answer 3

reduction in hip flexion/knee extension strength

Question 4

What kind of joint knee extensor is the vastus intermedius?

Answer 4

single joint knee extensor

Question 5

What effect of weakness does the vastus intermedius have?

Answer 5

decreased knee ext. strength

Question 6

What effect of tightness does the vastus intermedius have?

Answer 6

decreased knee flexion ROM

Question 7

Which is the largest of the quad muscles?

Answer 7

vastus lateralis

Question 8

What is the dominant knee extensor?

Answer 8

vastus lateralis

Question 9

What is the effect of weakness in the vastus lateralis?

Answer 9

reduced knee extension strength

Question 10

What is the effect of weakness in the vastus lateralis?

Answer 10

limits knee flexion ROM

Question 11

What % of knee extensor torque does the vastus medialis have?

Answer 11

10-12%

Question 12

What does the vastus medialis balance?

Answer 12

the pull of the heads of the quads

Question 13

What two knee extensors pull along the femur?

Answer 13

RF and VI

Question 14

What knee extensor pulls lateral quad?

Answer 14

VL

Question 15

Which muscle can balance with a medial pull?

Answer 15

only VM

Question 16

What is the effect of weakness in the vastus medialis?

Answer 16

lateral shift in patellar movement

Question 17

What is the effect of tightness in the vastus medialis?

Answer 17

contributes to decreased knee flexion ROM

Question 18

Strength in what muscle may protect knee joint degeneration?

Answer 18

quadriceps femoris

Question 19

What are the 5 main knee flexors?

Answer 19

hamstrings
popliteus
gracilis
sartorius
gastrocnemius

Question 20

What are the 4 muscles part of the hamstrings?

Answer 20

• Bicep femoris longus (long head)
• Bicep femoris brevis (short head)
• Semitendinosus
• Semimembranosus

Question 21

Which muscle of the hamstrings is the smallest but has the largest moment arm?

Answer 21

semitendinosus

Question 22

Which muscle of the hamstrings is the largest?

Answer 22

semimembranosus

Question 23

What do the hamstrings contribute to?

Answer 23

• medial/lateral rotation
• hip extension (not BF brevis)
• knee stability

Question 24

What are the 2 effects of weakness in the hamstrings?

Answer 24

• Loss of knee flexion strength
• Produces little disability (control of knee flexion in everyday activities usually by eccentric contraction of quads)

Question 25

What are the effects of tightness in the hamstrings?

Answer 25

* Limits knee extension ROM (hip flexed) * Limit hip flexion ROM (knee extended)

Question 26

What are the 5 main knee medial rotators?

Answer 26

- sartorius - gracilis - semitendinosus - semimembranosus - popliteus

Question 27

What are the 3 main knee lateral rotators?

Answer 27

- tensor fasciae latae - bicep femoris longus - bicep femoris brevis

Question 28

What is the function of the tensor fasciae latae?

Answer 28

* Can provide dynamic stabilization of the knee joint * Acts at both the hip and knee * Large hip abduction moment arm

Question 29

What is the effect of weakness in the tensor fasciae latae?

Answer 29

isolated weakness may not produce disability

Question 30

What are the effects of tightness in the tensor fasciae latae?

Answer 30

* Reduced ROM hip extension, adduction, lateral rotation (knee flexed) * Clinically challenging to identify (see Ober’s test) * Linked to excessive lateral deviation of the patella and anterior knee pain

Question 31

___ strength is greater than ___ strength

Answer 31

extension, flexion

Question 32

Why is extension strength greater than flexion strength?

Answer 32

because there is a greater mass of extensor muscles

Question 33

What is the ideal strength ratio of the extensor muscles?

Answer 33

45-65%

Question 34

What is the extension strength ratio affected by?

Answer 34

* Kneeposition * Mode of contraction * Speed of contraction * Sex

Question 35

What are the 4 factors affecting knee strength?

Answer 35

* Age * Sex * Genetics * Joint position