Limits of the MSK System - Ligaments and Tendons Flashcards
what is the most likely cause of ligament injuries?
traumatic rather than chronic
in what condition are ligament injuries difficult to study ?
in vivo - most of what we know is from simulation studies
where do most research on ligaments injuries come from ?
some implantable transducers but most estimates of stressors and strains come from commuter modelling studies
what is the most common location of ligament injury in the body ?
Anterior TaloFibular Ligament (ATFL)
what is the tensile strength of the ATFL ?
58 - 556 N
St Pierre et al., 1983
state 3 facts about ATFL injury
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
explain the healing process of ligaments
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
talk about the degree of ligament movement post injury
degree of movement post injury repair is greater due to ligament not repairing to the same degree of strength prior to the injury
state 3 facts about the repair of ligaments
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)
how is the ACL injured ?
traumatic mechanism (contact or non-contact)
how do you get medical imaging of ACL injuries ?
MRI scans
can tendons be measured in vivo ?
yes
state 2 invasive methods of investigating tendon failures
1) tendon buckle
2) fibre optics
state a non-invasive method of studying a failed tendon
ultrasound
strain damage to a tendon occurs at what level of stretch ?
5 - 12 %
state 2 additional facts of tendon healing that aren’t the same as in ligament healing
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
state 2 basic facts to how ultrasound works
- high frequency sound waves sent into tissue
- sound differentially reflected or absorbed by tissues of different densities
state 3 common sites of tendinopathy
1) Achilles tendon
2) patella tendon
3) tendon or origin of extensor carpi radialis brevis (lateral epicondylitis/tennis elbow)
state what it is meant by the key term - ‘tendinopathy’
a chronic, repetitive, strain injury at which the tendon has been loaded to high strain in order to accomplish its function
state 4 facts about tendinopathy
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
which is stiffer: a functional tendon or a tendinopathy tendon ?
Tendinopathic tendons have lower stiffness and greater cross-sectional area leading tom lower Young’s modulus (Ayra & Kulig., 2009)
state the formation of ligaments and tendon (different functions, same material)
- cells (fibroblasts)
- water (66% of weight)
- collagen (70-80% weight)
- proteoglycans
- elastin
- uniform structure
what does the strength of ligaments and tendons depend upon ?
the cross sectional area (CSA) of the material - the more collagen fibres, the more resistant the material to stretch
state the equation for ‘tensile stress’
tensile stress = force / CSA
state the equation for ‘strain’
strain = change in length / initial length
state the equation for ‘stiffness’
stiffness = force / change in length
when does a complete rupture of ligament occur ?
between 10-12% of strain
what is the ligament operating range ?
1.5 - 2.5%
what is the tendon operating range ?
2.5 - 7%
what architectural parameters make MTU’s different ?
1) size (mass or anatomical CSA)
2) fibre length
3) physiological CSA - fibre length and pennation angle
4) tendon length
state 3 facts about the MTU
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)
explain energy storage during the stance phase of running (5 points)
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
state the equation for ‘elastic energy stored’
elastic energy stored = 1/2 force x linear deformation
what determines how much a tendon will strain ?
the stiffness is its resistance to deformation dent a force
what 2 things cause tendon stiffness ?
1) dependent upon CSA
2) more collagen fibres, the greater the resistance to stretch
the stiffer the tendon, what 3 effects occur ?
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
explain ‘Hysteresis’ (4 points)
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
