Ligaments And Tendons Flashcards
What do tendons connect?
Muscle to bone
What do ligaments connect?
Bone to bone
What are ligaments function?
*Augment STATIC MECHANICAL STABILITY OF JOINTS
*PREVENTS XS ABNORMAL MOTION
SENSORY SOURCE, PROVE PROPRIOCEPTION FEEDBACK
What is the function of tendons?
TRANSMIT TENSILE LOAD TO BONE
ENABLE MUSCLE TO BE OPTIMAL DISTANCE FROM JOINT
STORE ENERGY
What are ligaments and tendon made of?
PARATENON- loose areolar tissue, protects and facilitates gliding. Major site of remodelling and healing responses- abundant cells and blood vessels (vascular tendons ) some tendons a synovial sheath replaces the paratenon - AVASCULAR tendons
EPITENON- a SYNOVIUM like membrane beneath paratenon for tendons with high frictional forces in Palm - increase gliding, by producing SYNOVIUM form synovial cells
ENDOTENON- binds fascicles ( groups of collagen bundles )
MICRO=
Cells-FIBROBLASTS
Extracellular matrix-
COLLAGEN 1( 70% tendons )
GROUND GLASS
ELASTINS ( > LIGAMENTS)
How is collagen synthesised?
As a PRECURSOR, PRO-COLLAGEN by FIBROBLASTS
SECRETED and CLEAVED extracellularly-> COLLAGEN
What type of collagen is within ligaments and tendons?
Type 1- 90%
How does collagen exist?
As 3 POLYPEPTIDE CHAINS
2 alpha 1
1 alpha 2
COMBINED TO FORM A RIGHT HANDED TRIPLE HELIX-> collagen molecule a ROD like shape
What are the x linkage between collagen molecules due to ?
Hydrogen bonds
What do several collagen fibres aggregate to form?
MICROFIBRILS (0.02-2um) in a quarter staggered way
What are further aggregation of MICROFIBRILS called?
Collagen fibres (1-20um) and bundles
What are lined between these bundles?
Fibroblasts in the direction of the ligament/ tendon function
What is the direction of collagen fibres in tendons? Why is this?
Parallel
To allow them to handle UNIDIRECTIONAL TENSILE LOADS
What direction are the collagen fibres in ligaments? Why is this?
Less parallel in layered arrangement with a single layer of fibres lying parallel but in subsequent layers they lie at different directions. Also crimped ( wavy pattern) to increase their capacity to absorb tension
To allow these structures to SUSTAIN PREDOMINANTLY TENSILE STRESSES IN 1 DIRECTION but also SMALLER STRESSES IN OTHER DIRECTION for any applied external force
What does the ground substance consist of? Can you draw it?
PROTEOGLYCANS
GLYCOPOROTEINS
PLASMA PROTEINS
What is the role of the PROTEOGLYCANS ?
That bind Extracellular water making the matrix a highly structured gel like material.
It also STABLISES the collagenous skeleton of the ligaments and tendons and contributes to overall strength
What is ELASTIN?
A HYDROPHOBIC NON GLYCOSLATED PROTEIN secreted by FIBROBLASTS into the Extracellular matrix
What does elastin do in ligaments and tendons ?
These hydrophobic nonglycosylated proteins form an extensive network with HIGHLY CROSS LINKED FILAMENTS and SHEETS which allow the network to STRETCH AND COIL
Up to 200%. Of the unloaded length at relatively low loads
What is the importance of elastin in tendons and ligaments ?
In the RECOVERY OF tissue after loading
Their function diminished towards max loading levels because their max strength is about 5x lower than collagen
Which does elastin have a greater content in tendons or ligaments ?
Ligaments
What are tendons and ligaments highly resistant too?
LENGTHENING
tendons also relatively FLEXIBLE and can angulated around bone surfaces/ deflect beneath retinacula total the direction
Are tendons stronger than ligaments? If so why?
Yes ligaments are weaker than tendons Due to the organization of fibres in layer not all fibres are stretched when loaded along the main fibre axis. Therefore weaker than tendons
Describe the structure of the insertion points for ligaments and tendons?
Divided into 4 ZONES ;
Zone 1- Parallel collagen fibres at end of the tendon/ligament
Zone 2- Collagen fibres INTERMESH with UNMINERALISED FIBROCARTILAGE
Zone 3- FIBROCARTILAGE GRADUALLY becomes MINERALISED
Zone 4-MINERALISED FIBROCARTILAGE MERGES into CORTICAL BONE
What crosses all 4 zones?
The perforating fibres of SHARPEY- connective tissue which strengthens the bony attachment
What’s the importance of the zones 1-4?
The change in structure properties -> INCREASED STIFFNESS
DECREASE STRESS CONCN-> reduces injuries at INSERTION SITE
What additional structure do tendon have to aid strength?
APONEUROSIS - within the muscle fascia.
-> LARGER SURFACE AREA for LOAD TRANSFER from muscle to tendon! with the orientation increasing the strength.
Describe blood supply to tendon / ligaments ?
Poor vascular supply cf bone/ skin
They have a lower metabolic rate
Mainly found at INSERTION SITES
runs LONGITUDINALLY and is UNIFORM
What is the blood supply in the paratenon?
Thru a SPARSE array of SMALL ARTERIOLES which run longitudinally fro adjacent muscles to arerolar connective tissue
What is the blood supply in AVASCULAR tendons ?
Why is this CLINCALLY important?
A VINCULA - MESOTENON - carries a vessel to supply
ONE TENDON SEGMENT - adjacent areas receive nutrition via diffusion
So PARATENON covered TENDONS HEAL BETTER than other Tendons
What is the nerve supply to tendons/ligaments ?
Mainly via AFERENT , with specialised afferent receptors. when these special receptors are activated during rapid increase in tension , myostatic reflexes are activated which inhibit development of excessive tension during muscular contraction.
Hence importance in proprioception role in overal neuromuscular control of the limb
What are the properties of ligament and tendons?
They are VISCOELASTIC - low loads viscous, high loads elastic=
Demonstrate stress-strain behaviour which is time and rate dependent - CREEP
STRESS RELAXATION
HYSTERESIS
STRESS/ strain rate
What factors affect the biomechanical properties of ligaments / tendons?
AGEING EFFECT- up to 20 yrs the no and quality of x linking increases -> increase tensile strength tendons and ligaments
>20 yrs- MEAN COLLAGEN DIAMETER/CONTENT DECREASE-> gradual DECLINE in MECHANICAL PROPERTIES
< puberty - weakest link ligament bone complex cf adult = mid substance failure
ENDOCRINE- INCREASE LAXITY /reduced stiffness in later stages of pregnancy.
PHARMACOLOGY- short term use of INDOMETHCAIN- increase tensile strength of tendons ? ^ of collagen x linkage
Corticosteriods - reduced biomechanical qualities
MOBILISATION/immobilisation
What are the 2 main types of injury?
REPETITIVE MICROTRAUMA
MACROTRAUMA
Describe what happens in Repetitive microtrauma ?
FATIGUE FAILURE occurs due to Repetitive Loading well below the normal ULTIMATE TENSILE STRENGTH
-> MICROTEARS followed by an INFLAMMATORY REACTION ( in an attempt to heal) + Sometime CALCIFICATION -which alters the biomechanical properties
Often occurs in tendon since they carry higher loads invivo
Described how macro-trauma causes injury in tendons/ ligaments ?
ACUTE FAILURE due to FORCES above the ULTIMATE TENSILE STRENGTH-> PARTIAL/ COMPLETE RUPTURE
normally gd mechanism of injury
At a low loading rate where is the weakest part of the tendon/ligament ?
BONY INSERTION
What is the weakest points in a tendon/ligament when a high load is applied?
The tendon / ligament
Suggests at a higher strain rate the strongest part is the bone/ligament complex
Where do the ligament avulsion occur?
Between zones 2/3- between UNMINERALISED and MINERALISED FIBROCARTILAGE LAYERS
In tendons what other 2 factors contribute to injury?
1) CROSS SECTIONAL AREA OF THE TENDON cf ITS MUSCLE- strength of tendon/ muscle depends on x sa- the larger xsa of muscle the stronger the force produced by the contraction and greater the tensile loads transmitted thru the tendon. Same larger xsa of tendon the greater the load it can bear. If tendons greater xsa cfmuscke likely the muscle with rupture.
2) . AMOUNT of FORCE PRODUCED BY CONTRACTION of the MUSCLE to which the TENDON IS ATTACHED- when muscle max contracted, the tensile stress on tendon is highest. This stress can be increased if ECCENTRIC contraction of the muscle cf CONCENTRIC- > load imposed on the tendon may exceed the yield point -> tendon rupture
How can you categorize the injury to tendons/ligaments ?
Grade 1- mild- some pain but no joint laxity clinically
Grade 2- moderate- severe pain and some joint laxity clinically
PROGESSIVE failure of collagen taken place->partial rupture
Grade 3- severe - severe pain occurs at trauma, less pain post, clinically completely unstable- most collagen fibres have ruptured
Can you describe the stages of healing of ligaments/ tendons?
1) HAEMORRHAGIC/ INFLAMMATORY - formation of a HEMATOMA within DAMAGED region and intimation of a RAPID INFLAMMATORY RESPONSE -> invasion of polymorphous nuclear cells and monocytes/ macrophages-> released of cytokines and growth factors. Monocytes remove debris and FIBROELASTIC CELLS begin to appear. Last few hours-days
2) PROLIFERATION - new blood vessels are formed and fibroblasts recruited from local environment/ circulation -> new collagen matrix- initially type 3. New matrix increases in mass and becomes less viscous and more elastic as inflammation decreases - weeks
3) REMODELLING- starts within weeks of injury , lasts years.
Characterised by PROGRESSIVE MATURATION and CONVERSION OF COLLAGEN from TYPE 3 to TYPE 1, REORIENTATION IN RESPONSE TO LOADS and REORGANISATION OF MATRIX
When are surgical tendon repairs weakest?
In the first week, regaining most of their strength by 3-4 weeks and MAX STRENGTH at 6 MONTHS
What factors affect healing of ligaments/ tendons?
1)MOBILISATION- ligaments and tendons appear to remodel IN RESPONSE TO MECHANICAL DEMANDS placed upon them. Controlled movement- has benefit of healing , increasing TENSILE STRENGTH of tendons and lig- bone interface by stimulating SYNTHESIS of COLLAGEN and PROTEOGLYCAN
weaker if immobilise- more immature collagen produced-> weaker
2) SURGERY- calibre of suture, suture strands suture technique and peripheral epitendinous or sheath repair effects the strength of the healing process.
3) BIOLOGICAL / BIOCHEMICAL MANIPULATION- using growth factors - epidermal growth factor and platelet derived growth factor increase FIBROBLAST proliferation invitro. Steriods and hyaluronate - decrease adhesions but decrease rate and strength of healing and increase infection.
4) Joint INSTABILTY -in an unstable joint the healing is inferior
