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Basic Science > Ligaments and tendons > Flashcards

Ligaments and tendons Flashcards

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1
Q

What are ligaments?

A
  • Connect bone with bone
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2
Q

What is the function of ligaments?

A
  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
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3
Q

What are tendons?

A
  • Attach muscle to bone
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4
Q

What is the function of tendons?

A
  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)
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5
Q

What are ligaments and tendons composed of?

A
  • Cells - fibroblasts 20% of tissue volume
  • Extracellular matrix- 80%
    • ** collagen**
    • ground glass= proteogylcans/elastin
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6
Q

Which has more elastin ligaments or tendons?

A
  • Ligaments
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7
Q

Which has more collagen ligaments or tendons?

A
  • Collagen content is high over 70% in Tendons cf ligaments
  • exeptions
    • ligamentum nuchae
    • ligamentum flava along spinal column
    • contain large no of elastin
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8
Q

How is collagen synthesised?

A
  • As a precursor, Procollagen by fibroblasts
  • Then secreted and cleaved extra-cellularly-> collagen fibres
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9
Q

What type of collagen is in ligaments and tendons?

A
  • Type 1
  • <10% type 3
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10
Q

Describe the structure of type 1 collagen?

A
  • 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
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11
Q

What do several collagen molescules form?

A
  • in a quarter staggered array -> microfibrils
  • each 0.02-0.2µm in diameter
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12
Q

What do aggregation of microfibres lead to?

A
  • Collagen Fibres
  • 1-20µm
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13
Q

What do aggreagations of fibres lead to ?

A
  • Bundles
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14
Q

What is the alignment of the fibrobasts in these bundles?

A
  • between the bundles in the direction of the ligament or tendon function
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15
Q

What is the arrangement of the collagen fibres in tendons?

Why is this so?

A
  • Parallel
  • To allow them to handle high unidrectional (uni-axial ) tensile loads
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16
Q

What is the arrangement of collagen fibres in ligaments?

A
  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
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17
Q

What does the ground glass substance consist of?

A
  • 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
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18
Q

What is the role of the the proteoglycans?

A
  • 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
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19
Q

What does elastin consists of?

A
  • Hydrophobic, non glycosylated proteins
  • secreted by fibroblasts into the ECM
20
Q

What do the elastin proteins form?

A
  • 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
21
Q

What are tendons and ligaments surrounded by?

What is its function?

A
  • 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)
22
Q

What is beneath the paratenon?

What is its function?

A
  • 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
23
Q

What is beneath the epitenon?

A
  • Endotenon
    • which in turn binds together the collagen fasicles ( group of collagen bundles)
24
Q

What are tendons and ligaments resistant too?

A
  • Lengthening
25
Q

Which are stronger ligaments or tendons ? why?

A
  • 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
26
Q

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

A
  • 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
27
Q

What structure crosses all 4 zones of insertion?

A
  • Perforating fibres of Sharpey
28
Q

What is the advantage of the 4 zones of insertion?

A
  • The gradual change in structural properties results in increased stiffness and decreased stress concentration, minimising injuries at insertion sites
29
Q

What is also important in tendons?

A
  • 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
30
Q

What is the blood supply to tendons/ligaments?

A
  • 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
31
Q

What is the consequence of different vascular supplies to tendons?

A
  • Paratenons covered tendons heal better than other tendons
32
Q

Describe the nerve suppy to tendons/ligaments?

A
  • 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
33
Q

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

A
  • 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
34
Q

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

A
  • Low loads- viscuous
  • High loads- elastic
35
Q

What are the properties of visco-elastic behaviour?

A
  • 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
36
Q

What factors afect the biomechanical properties of ligaments/tendons/

A
  • 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
37
Q

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

A
  • At the musculoskeletal junction due to stress concentration and relatively weak muscular tissue
38
Q

What are the mechanisms of injury of tendons/ligaments?

A
  • 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
39
Q

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

A
  • Tendon/ligament bone complex
40
Q

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

A
  • The tendon or ligament
41
Q

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

A
  • 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)
42
Q

Decribe the grading of tendon/ligament injury?

A
  • 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
43
Q

Describe the 3 phases of healing in ligament and tendons?

A
  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
44
Q

When are ligament/tendon repairs their weakest?

A
  • **First week **
  • regain most of their strength at 3-4 weeks
  • Max strength regained at 6 months
45
Q

What factors affect healing of tendons/ig?

A
  • 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

Basic Science (31 decks)

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