Ligaments and tendons

Question 1

What are ligaments?

Answer 1

• Connect bone with bone

Question 2

What is the function of ligaments?

Answer 2

1. Augment static mechanical stability of joints
2. to prevent excessive or abnormal motion
3. as a sensory source for proprioceptive feedback about movement and posture, thereby contributing to neuromuscular dynamic

Question 3

What are tendons?

Answer 3

• Attach muscle to bone

Question 4

What is the function of tendons?

Answer 4

1. Transmit tensile load from muscle to bone
2. **enable the muscle belly to be at an optimal distance from the joint without an extended length of muscle **
3. As a strore of energy ( analogous to a spring)

Question 5

What are ligaments and tendons composed of?

Answer 5

• Cells - fibroblasts 20% of tissue volume
• Extracellular matrix- 80%
  
  • ** collagen**
  • ground glass= proteogylcans/elastin

Question 6

Which has more elastin ligaments or tendons?

Answer 6

• Ligaments

Question 7

Which has more collagen ligaments or tendons?

Answer 7

• Collagen content is high over 70% in Tendons cf ligaments
• exeptions
  
  • ligamentum nuchae
  • ligamentum flava along spinal column
  • contain large no of elastin

Question 8

How is collagen synthesised?

Answer 8

• As a precursor, Procollagen by fibroblasts
• Then secreted and cleaved extra-cellularly-> collagen fibres

Question 9

What type of collagen is in ligaments and tendons?

Answer 9

• Type 1
• <10% type 3

Question 10

Describe the structure of type 1 collagen?

Answer 10

• 3 polypeptide chains
  
  • 2 xalpha 1
  • 1x alpha 2
• Combined to form a Right handed triple helix => collagen molecules a rod like shape
• Intra and interchain bonding or cross linking ( due to Hydrogen bonds) provide stability to the molecule

Question 11

What do several collagen molescules form?

Answer 11

• in a quarter staggered array -> microfibrils
• each 0.02-0.2µm in diameter

Question 12

What do aggregation of microfibres lead to?

Answer 12

• Collagen Fibres
• 1-20µm

Question 13

What do aggreagations of fibres lead to ?

Answer 13

• Bundles

Question 14

What is the alignment of the fibrobasts in these bundles?

Answer 14

• between the bundles in the direction of the ligament or tendon function

Question 15

What is the arrangement of the collagen fibres in tendons?

Why is this so?

Answer 15

• Parallel
• To allow them to handle high unidrectional (uni-axial ) tensile loads

Question 16

What is the arrangement of collagen fibres in ligaments?

Answer 16

1. Less parallel
2. Layered arrangement

• any single layer fibres parallel to each other but in subsequent layers they lie in different directions
• allows sustain predominantly tensile stresses in one direction but also smaller stresses in another direction for any applied force

1. Crimped/ Wavy pattern
   
   • ​​increasing ability to absorb energy

Question 17

What does the ground glass substance consist of?

Answer 17

• Proteoglycans
  
  • ​composed of sulphated polysaccharide chains ( glycoaminoglycans) bound to a core protein, which is in turn bound to a link protein to a hyaluronic acid chain to form an extremely high molecule weight PG aggregate
• Glycoproteins
• Plasma proteins

Question 18

What is the role of the the proteoglycans?

Answer 18

• Bind most of the extracellular water of the ligaments and tendons
• Making a matrix a high structured gel-like material
• acting like a cement like substance between the colagen microfibrils they help to stabilise the collagenous skeleton of tendons and ligaments
• contribute to overall strength

Question 19

What does elastin consists of?

Answer 19

• Hydrophobic, non glycosylated proteins
• secreted by fibroblasts into the ECM

Question 20

What do the elastin proteins form?

Answer 20

• Extensive network with highly crossed- linked filaments and sheets
• allow the network to stretch and coil ( up to 200% of their uploaded length at relatively low loads)
• their function diminishes towatds max loading levels because their maximum strength is about x5 than that of collagen

Question 21

What are tendons and ligaments surrounded by?

What is its function?

Answer 21

• Loose areolar connective tissue = Paratenon

Function

• it protects the tendon
• Facilitates glide
• major source of remodelling and healing responses as it contains abundant cells and blood vessels ( vascular tendon)

Question 22

What is beneath the paratenon?

What is its function?

Answer 22

• Epitenon
  
  • a synovium like membrane
  • found in tendons that are particularly subjected to high friction forces ( palm and wrist)

Function

• enhances glide- by providing synovial fluid from its synoval cells

Question 23

What is beneath the epitenon?

Answer 23

• Endotenon
  
  • which in turn binds together the collagen fasicles ( group of collagen bundles)

Question 24

What are tendons and ligaments resistant too?

Answer 24

• Lengthening

Question 25

Which are stronger ligaments or tendons ? why?

Answer 25

• Ligaments are less strong than tendons
• due to organisation of the fibres in layers not all the fibres are stretched when loaded along the main fibre axis

Question 26

What is the structure of the insertion of tendons/ligaments into bone?

Answer 26

• 4 zones of Indirect insertion
• zone 1: parallel collagen fibres at end of the tendon/lig
• Zone 2: collagen fibres intermesh with unmineralised fibrocartilage
• Zone 3: Fibrocartilage gradually becomes mineralised
• Zone 4: Mineralised fibrocartilage merges into cortical bone

Question 27

What structure crosses all 4 zones of insertion?

Answer 27

• Perforating fibres of Sharpey

Question 28

What is the advantage of the 4 zones of insertion?

Answer 28

• The gradual change in structural properties results in increased stiffness and decreased stress concentration, minimising injuries at insertion sites

Question 29

What is also important in tendons?

Answer 29

• The musculotendinous junction
  
  • since high local stresses can occur here, predisposing to injury
• Tendons also have internal portion within muscle fascia aka aponeurosis
  
  • provides a large surface area for load transfer from muscle to tendon
  • the orientation of this junction enhances its strength

Question 30

What is the blood supply to tendons/ligaments?

Answer 30

• Poor
• orginates mainly at insertion sites
• runs longitudinally thru ligament
• Uniform
• **paratenon covered tendons- sparse aray of small arterioles run longitudinally **
• in sheathed avascular tendons a vincular ( mesotenon) carries a vessel to supply one tendon segement. Adjacent avascular areas recieve nutrition by diffusion

Question 31

What is the consequence of different vascular supplies to tendons?

Answer 31

• Paratenons covered tendons heal better than other tendons

Question 32

Describe the nerve suppy to tendons/ligaments?

Answer 32

• mainly Afferent
• with specialised afferent receptors
• these receptors are activated during rapid increase in tension, myotactic reflexes are initiated, which inhibit the development of excessive tensions during muscle contractions

Question 33

Can you draw the stress /strain curve for ligaments and tendons?

Answer 33

• toe in region ( non linear region)
  
  • little resistance to tension as the fibres lengthen but as elongation progresses an increasing number of fibrils become taut and carry load
  • a thigher loads the stiffness of the tissue increases and progressively greater force is required to produce equivalent amounts of elongation = linear region- as the deformation of the tissue has a more or less linear relationship with load
  • dips- small force reduction can be seen at the end of linear region.
    
    • caused by early sequential failure of a few greatly stretched fibre bundles
    • as elongation exceeds capacity of the fibres, yield and failure of the tissues results from progressive fibril failure.
    • this when the curve begins to bend towards the strain axis
  • A point of ultimate tensile strength is Pmax is reached
  • complete failure then occurs rapidly
  • NB not all ligaments /tendons behave the same
  • ligamentum falvum has high elastin- elongation of specimen reaches 50% before stiffness increases appreciately, at 70% elongation the stiffness increases greatly then fails abruptly

Question 34

What properties do tendons and ligaments show in low loads cf high loads?

Answer 34

• Low loads- viscuous
• High loads- elastic

Question 35

What are the properties of visco-elastic behaviour?

Answer 35

• Hysteresis
  
  • load elongation curve differs during loading and unloading -> net energy loss= usually heat
• Stress relaxation
  
  • time dependent reduction in stress over a constant strain
  • argument for cyclic loading o fhamstring before fixation
• Creep
  
  • time dependent increase in deformation under a constant stress
  • ponsetti method for correctio of cavus feet

Question 36

What factors afect the biomechanical properties of ligaments/tendons/

Answer 36

• Ageing effect
  
  • during maturation the number and quality of x links increases-> increase in tensile strength
  • after maturation
    
    • the mean collagen diameter and content decrease-> gradual decline of mechanical properties
• Endocrine effect
  
  • later stages of pregnancy-. increased laxity & decreased stiffness of tendon adn lig noted in pelvic region
• Pharamacologial effect
  
  • short term use of indomethacin increases tensile strength tendons ? x linkage of collagen molecules
• Mobilisation and immobilisation

Question 37

In the adolsecnet and older children where does avulsion of tendons/ligaments occurs?

Answer 37

• At the musculoskeletal junction due to stress concentration and relatively weak muscular tissue

Question 38

What are the mechanisms of injury of tendons/ligaments?

Answer 38

• Repetitive microtrauma
  
  • fatigue failure occurs due to repeititve loading well below the normal ultimate tensile strength
  • these -> microtears followed by inflammatory reaction ( in attempt to heal) then calcification => alters biomechanical properties of tissue
  • often in tendons cf ligaments as carry higher loads in vivo
• Macro-trauma
  
  • acute failure due to forces exceeding the ultimate tensile strength -> partial or complete rupture

Question 39

Where is the weakest component of the ligament/tendon in low loading rate?

Answer 39

• Tendon/ligament bone complex

Question 40

Where is the weakest component of the ligament/tendon in high loading rate?

Answer 40

• The tendon or ligament

Question 41

Name the 2 other factors in tendons that contribute to the nature of the injury?

Answer 41

• Cross sectional area of the tendon in realtion to its muscle
  
  • the larger x sectional acrea of muscle the stronger the force produced by the contraction so the greater the tensile loads transmitted thru the tendon
  • similar the larger the x sectional ares of the tendon the greater load it can bear
  • if tensile strength of a tendon is > than muscle then muscle ruptures are more liely to occur
• Amount of force produced by the contraction of muscle to which the tendon is atttached
  
  • when muscle contracted, the tensile stress on tendon is highest
  • this can be increased in concentric loading ( shortening of muscle) cf eccentric loading ( lengthening of muscle in deceleration)

Question 42

Decribe the grading of tendon/ligament injury?

Answer 42

• Grade 1- mild some pain, no joint laxity detected
• grade 2- moderate, severe pain and some joint laxity. partial rupture. Some joint laxity hidden by muscles
• grade 3- severe, severe pain at time of trauma, less pain post injury. unstable joint. most collagen fibres ruptured

Question 43

Describe the 3 phases of healing in ligament and tendons?

Answer 43

1. Phase one - haemorrhagic /inflammatory phase

• formation of haematoma within damaged region and commensing of rapid inflammatory response
• invasion of Polymorphorous cells adn monocytes/macrophages with release of cytokines and growth factors. monocytes remove debris and fibroblastic cells appear. hours-days

2. phase 2- Proliferation phase

• New blood vessels are formed & fibroblasts recruited from local environment and circulation -> new matrix material- type 3 collagen
• new matrix increases in mass
• becomes less viscious and more elastic

​3. Phase 3- remodelling phase

• within wks of injury- last up to years
• progression of maturation and conversion of collagen to type 1
• alignment in more physiological orientation ( in response to loads) and reorganisation of matrix

Question 44

When are ligament/tendon repairs their weakest?

Answer 44

• **First week **
• regain most of their strength at 3-4 weeks
• Max strength regained at 6 months

Question 45

What factors affect healing of tendons/ig?

Answer 45

• mobilisation
  
  • lig/tendon remodel in response to mechanical loads placed upon them.
  • controlled movement has benefits on healing
  • increasing tensile strength and ligament - bone interface by stimulating syn of collagen and proteoglycan and promoting proper collagen fibre orientation
  • immobilisation->decreased strength/ increased stiffness/ more immature collagen with decreased amount and quality of cross links between collagen molecules
• Surgery
  
  • calibre of suture
  • no of suture strands
  • suture technique
  • use of peripheral epitendinous or sheath repair
• Biological and biomechanical manipulation
  
  • ​Platelet derived growth factor increase fibroblast proliferation in vitro
  • steriods and hyaluronate - decrease adhesions but decrease rate and strength of tendon healing
• Joint stability
  
  • in unstable joint , healing of lig is inferior