Ligaments and tendons Flashcards
1
Q
What are ligaments?
A
- Connect bone with bone
2
Q
What is the function of ligaments?
A
- Augment static mechanical stability of joints
- to prevent excessive or abnormal motion
- as a sensory source for proprioceptive feedback about movement and posture, thereby contributing to neuromuscular dynamic
3
Q
What are tendons?
A
- Attach muscle to bone
4
Q
What is the function of tendons?
A
- Transmit tensile load from muscle to bone
- **enable the muscle belly to be at an optimal distance from the joint without an extended length of muscle **
- As a strore of energy ( analogous to a spring)
5
Q
What are ligaments and tendons composed of?
A
- Cells - fibroblasts 20% of tissue volume
-
Extracellular matrix- 80%
- ** collagen**
- ground glass= proteogylcans/elastin
6
Q
Which has more elastin ligaments or tendons?
A
- Ligaments
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
8
Q
How is collagen synthesised?
A
- As a precursor, Procollagen by fibroblasts
- Then secreted and cleaved extra-cellularly-> collagen fibres
9
Q
What type of collagen is in ligaments and tendons?
A
- Type 1
- <10% type 3
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
11
Q
What do several collagen molescules form?
A
- in a quarter staggered array -> microfibrils
- each 0.02-0.2µm in diameter
12
Q
What do aggregation of microfibres lead to?
A
- Collagen Fibres
- 1-20µm
13
Q
What do aggreagations of fibres lead to ?
A
- Bundles
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
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
16
Q
What is the arrangement of collagen fibres in ligaments?
A
- Less parallel
- 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
-
Crimped/ Wavy pattern
- increasing ability to absorb energy
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
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
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
Which are stronger ligaments or tendons ? why?
* **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
What is the structure of the insertion of tendons/ligaments into bone?
* 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
What structure crosses all 4 zones of insertion?
* **Perforating fibres of Sharpey**
28
What is the advantage of the 4 zones of insertion?
* The gradual change in structural properties results in increased stiffness and decreased stress concentration, minimising injuries at insertion sites
29
What is also important in tendons?
* 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
What is the blood supply to tendons/ligaments?
* Poor
* orginates mainly at **insertion sites**
* runs **longitudinally** thru ligament
* **Uniform**
* **paratenon covered tendons- sparse aray of small arterioles run longitudinally **
* **i**_n sheathed avascular tendons_ **a vincular ( mesotenon) carries a vessel to supply one tendon segement**. Adjacent avascular areas recieve nutrition by diffusion
31
What is the consequence of different vascular supplies to tendons?
* **Paratenons covered tendons heal better** than other tendons
32
Describe the nerve suppy to tendons/ligaments?
* 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
Can you draw the stress /strain curve for ligaments and tendons?
* 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
What properties do tendons and ligaments show in low loads cf high loads?
* Low loads- viscuous
* High loads- elastic
35
What are the properties of visco-elastic behaviour?
* ***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
What factors afect the biomechanical properties of ligaments/tendons/
* **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
In the adolsecnet and older children where does avulsion of tendons/ligaments occurs?
* At the **musculoskeletal junction** due to stress concentration and relatively weak muscular tissue
38
What are the mechanisms of injury of tendons/ligaments?
* **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
Where is the weakest component of the ligament/tendon in low loading rate?
* Tendon/ligament bone complex
40
Where is the weakest component of the ligament/tendon in high loading rate?
* **The tendon or ligament**
41
Name the 2 other factors in tendons that contribute to the nature of the injury?
* **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
Decribe the grading of tendon/ligament injury?
* 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
Describe the 3 phases of healing in ligament and tendons?
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
When are ligament/tendon repairs their weakest?
* **First week **
* regain most of their strength at 3-4 weeks
* Max strength regained at 6 months
45
What factors affect healing of tendons/ig?
* **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
