Limits of the MSK System - Ligaments and Tendons

Question 1

what is the most likely cause of ligament injuries?

Answer 1

traumatic rather than chronic

Question 2

in what condition are ligament injuries difficult to study ?

Answer 2

in vivo - most of what we know is from simulation studies

Question 3

where do most research on ligaments injuries come from ?

Answer 3

some implantable transducers but most estimates of stressors and strains come from commuter modelling studies

Question 4

what is the most common location of ligament injury in the body ?

Answer 4

Anterior TaloFibular Ligament (ATFL)

Question 5

what is the tensile strength of the ATFL ?

Answer 5

58 - 556 N

St Pierre et al., 1983

Question 6

state 3 facts about ATFL injury

Answer 6

1) mostly common due to forced inversion of ankle
2) strained to largest degree and has a smaller corss-sectional area than other lateral ligaments on the foot
3) due to combination of inversion and internal rotation, puts high strain on ATFL and to the lesser extent the CFL

Question 7

explain the healing process of ligaments

Answer 7

1) include of cells - inflammation (causes pain due to pressure)
2) new collagen formed - not normal alignment due to quick response - forms scar tissue
3) scar tissue slowly remodel to ‘normal’ - can take years

Question 8

talk about the degree of ligament movement post injury

Answer 8

degree of movement post injury repair is greater due to ligament not repairing to the same degree of strength prior to the injury

Question 9

state 3 facts about the repair of ligaments

Answer 9

1) healing ligament requires the two broken ends to be apposed (close to each other)
2) if not, surgical repair is required
3) ankle sprains can usually be managed conservatively (i.e. - without surgery)

Question 10

how is the ACL injured ?

Answer 10

traumatic mechanism (contact or non-contact)

Question 11

how do you get medical imaging of ACL injuries ?

Answer 11

MRI scans

Question 12

can tendons be measured in vivo ?

Answer 12

yes

Question 13

state 2 invasive methods of investigating tendon failures

Answer 13

1) tendon buckle

2) fibre optics

Question 14

state a non-invasive method of studying a failed tendon

Answer 14

ultrasound

Question 15

strain damage to a tendon occurs at what level of stretch ?

Answer 15

5 - 12 %

Question 16

state 2 additional facts of tendon healing that aren’t the same as in ligament healing

Answer 16

1) if the failure of the structure is partial, or the ends of the ruptured tissue are apposed, the ligament/tendon will heal
2) if not, surgery will be required

Question 17

state 2 basic facts to how ultrasound works

Answer 17

• high frequency sound waves sent into tissue

- sound differentially reflected or absorbed by tissues of different densities

Question 18

state 3 common sites of tendinopathy

Answer 18

1) Achilles tendon
2) patella tendon
3) tendon or origin of extensor carpi radialis brevis (lateral epicondylitis/tennis elbow)

Question 19

state what it is meant by the key term - ‘tendinopathy’

Answer 19

a chronic, repetitive, strain injury at which the tendon has been loaded to high strain in order to accomplish its function

Question 20

state 4 facts about tendinopathy

Answer 20

1) high strains close to fascicle failure limits
2) loading cycle repeats thousands of times in an exercise bout
3) fundamentally related to mechanical overload
4) anatomical, biochemical, and molecular changes associated with tendinopathy occur due to attempt to remodel

Question 21

which is stiffer: a functional tendon or a tendinopathy tendon ?

Answer 21

Tendinopathic tendons have lower stiffness and greater cross-sectional area leading tom lower Young’s modulus (Ayra & Kulig., 2009)

Question 22

state the formation of ligaments and tendon (different functions, same material)

Answer 22

• cells (fibroblasts)
• water (66% of weight)
• collagen (70-80% weight)
• proteoglycans
• elastin
• uniform structure

Question 23

what does the strength of ligaments and tendons depend upon ?

Answer 23

the cross sectional area (CSA) of the material - the more collagen fibres, the more resistant the material to stretch

Question 24

state the equation for ‘tensile stress’

Answer 24

tensile stress = force / CSA

Question 25

state the equation for ‘strain’

Answer 25

strain = change in length / initial length

Question 26

state the equation for ‘stiffness’

Answer 26

stiffness = force / change in length

Question 27

when does a complete rupture of ligament occur ?

Answer 27

between 10-12% of strain

Question 28

what is the ligament operating range ?

Answer 28

1.5 - 2.5%

Question 29

what is the tendon operating range ?

Answer 29

2.5 - 7%

Question 30

what architectural parameters make MTU’s different ?

Answer 30

1) size (mass or anatomical CSA)
2) fibre length
3) physiological CSA - fibre length and pennation angle
4) tendon length

Question 31

state 3 facts about the MTU

Answer 31

1) ratio of muscle fibre length to tendon length varies depending on muscle function
2) long fibres and short tension crease large active range of motion at joints (hip, knee, shoulder, elbow)
3) shorter fibres and long tendon important for elastic energy storage and return (ankle)

Question 32

explain energy storage during the stance phase of running (5 points)

Answer 32

1) KE and PE decrease in early stance
2) KE and PE lower at mid stance
3) energy stored like springs
4) springs recoil in late stance to return elastic energy to KE and PE
5) reduces amount of work done by muscles to accelerate the body during each stride

Question 33

state the equation for ‘elastic energy stored’

Answer 33

elastic energy stored = 1/2 force x linear deformation

Question 34

what determines how much a tendon will strain ?

Answer 34

the stiffness is its resistance to deformation dent a force

Question 35

what 2 things cause tendon stiffness ?

Answer 35

1) dependent upon CSA

2) more collagen fibres, the greater the resistance to stretch

Question 36

the stiffer the tendon, what 3 effects occur ?

Answer 36

1) the more force it can withstand/transmit
2) the less it will strain for a given force
3) the less energy it will store for a given force

Question 37

explain ‘Hysteresis’ (4 points)

Answer 37

1) tendon not perfectly elastic structure
2) approximately 7% energy lost due to heat
3) temp in Achilles tendon during 30 min run is 41℃
4) therefore, tendons heat up which may lead to damage