Tendons and ligaments

Function of tendons

1. Absorb, store, release energy → maximise exercise efficiency 

2. Power amplification ( store slow when it stretches + release fast ) 

3. Protection from damage( power attenuation

Function of ligaments

Transmit tensile forces from bone to bone 

→ strength to provide stability → high joint ROM 

→ flexibility to permit joint movement → at low joint ROM

Linkage of tendon features + biomechanical function

High tensile  elasticity + fatigue resistant

Function: Energy storage

Buffer: tendon lengthens before muscle to prevent eccentric damage while walking/ jumping

Amplifier stores energy in stance + quickly releases energy in push off to propel to next stage

What is enthesis + how it affects biomechanical performance

Description: Tendon/ ligament to bone insertion 

→ Fibrous ( insert directly on long bone )

→ fibrocartilaginous( 4 distinct zones w/ gradual transition ) 

→ muscular ( attachment of muscle to bone w/o tendon )

Effect: Aids load transfer bwt elastic tendon/ ligament + rigid bone

What is the muscle tendon junction + what structural adaptations are there

Description: abrupt transition from muscle to tendon

Adaptation:  Collagen fibres + muscle cells interdigitate to increase surface area 

→ reduction of stress bwt tendon + muscle + prevent damage

Composition of connective fibres

Component	Description
Collagen	Type I : predominant collagen in tendons  TYpe III: second most predominant
Elastin	3-D branching pattern → elastic + fatigue resistant  → store + return energy  → resist transverse + shear deformation in ligaments
Proteoglycan	Decorin: most abundant in tendon → help transfer loads bwt collagen fibrils + regulate fibrillogenesis Lubricin: provide lubrication to glide at tendon surface

Compare the composition + structure of ligaments + tendons:

	Compositon	Collagen type	Elastin	Proteoglycan	Structure
Ligament	ECM > fibroblasts	Type I/ III/ IV/ V	Varying amounts	/	Varied → resist force from multiple directions
Tendon		Less type III than ligament	Small	Mainly decorin	Aligned along long axis

Differences of tendons + ligaments on stress strain curve 

	Toe region	Elastic modulus	Failure mode
Tendon	Smaller	Steeper → stiffer	Fail all in one go
Ligament		Less steep	Progressive failure

Gender differences in ligaments + tendons

Ligaments

1. Ruptures at shorter length 

2. Ruptures at lower loads 

3. More compliant 

4. Absorb less energy 

5. Strength imbalances in hamstrings + quads

Effects of exercise on tendon properties

High magnitude load + long duration —> increase in size and stiffness

Isometeric at long muscle lengths + concentric + eccentricc + resistance + plyometric —> increase stiffness

Healing process of ligaments ( triphasic )

Inflammation phase:

1. Defect filled w/ vascular inflammatory tissue

   Proliferation:

   Inflammatory cells subsided + active fibroblasts dominated 

   Remodelling:

   1. Decreased in number and size of fibroblasts

   2. Remodelling → increased re-alignment  

   3. Cells remained larger + more numerous

Mechanical properties + morphology changes in ligaments after injury

Mechanical properties: 

1. Decreased stiffness 

2. Decreased load at failure 

3. Altered site of failure → whole ligament weakened → previously injured ligaments fail at midsubstance 

4. Inferior mechanical properties to normal ligament for 1 year 

5. Healed ligaments: ↑ CSA + less strong

Morphology: 

1. Increased cross-sectional area 

2. Progressive decrease in CSA from 3-24 weaks 

3. Laxity increased

Mechanism of tendon injury

1. Excessive force 

2. Repeated overload 

3. Normal forces applied to weakened tendon

   —> Stress shielding → some fibres may be overloaded while others underloaded 

4. Forces applied in alternative direction → compressive loading X for tendons 

Rehabilitation of tendons

1. Exercise → reduce pain + increase loading capacity → progressive loading to remodel tendon 

→ improve function

2. Avoid compressive loading if insertional tendinopathy 

3. Long duration 

X immobilisation: bc

1. Reduce structural properties of tendons/ ligaments 

2. Decrease in tissue stiffness → less deterioration if immobilised in tension

→ healing characteristics: slow ( hypovascular + hypocellular ) + may not attain past characteristics + insertion sites more resistant to recovery

Effect of altered loading on tendon

Appropriate loading: tendon improves structure → stiffer → X become thicker

Unloaded: superficial part of tendon overloaded + deep part stress shielded → stress shielded tendon becomes reactive →  thicken → increase number cells + ECM → load excessive → disrepair → continue to thicken +new  blood vessels formed + separation of collagen fibres → load still unchanged → degenerative tendon –. cell death ( can be reversed ; continuum of tendinopathy )

Features of maturation of tendons

1. Larger + stiffer tendon 

→ increase in collagen fibril + diameter 

→ increased cross sectional area 

2. Different modes of failure  asynchronous maturation

→ before skeletal maturity: avulsion injuries → strength of mid substance > bone tendon junction 

→ matured: failure in tendon mid-substance bc mechanical properties even out

Features of tendons in aging

Decrease in contractile force  Decrease in rate of force development  bc decrease in stiffness  Very limited tissue turnover → low self renewal potential