Tissue Mechanics Flashcards
Loading Modes
Compression; Tension; Bending; Shear; Torsion; Combined Loading
Structure of connective tissues
Characterized by a wide dispersion of cells in the presence of a large ECM
Interfibrillar components
(Ground substance)
Fibrillar components
(fibrous)
Connective tissues are unique because…
Functions determined by ECM, unlike other tissues where cell behavior determines
Fibroblast
Basic cells of most connective tissue
Fibroblasts may become
Chondroblast
Osteoblast
Tenoblast
With maturation, fibroblasts are…
Fibrocytes
Chondrocytes
Oesteocytes
Tenocytes
Proteoglycans
Attached are one or more polysaccaride chains called glycosaminoglycans (GAGs)
Glycoproteins
Compound containing a carbohydrate covalently linked to protein
GAGs
Negatively charged, a concentration of GAGs creates a swelling pressure and H20 goes into ECF
Collagen fibers counteract GAGs by
resisting and containing the swelling via tensile stress and osmotic pressure
Tissue can resist compression
Tissues subjected to high compression forces have a ___ PG content
High
Tissues that resist tensile loads have a ____ PG content
Low
Collagen
Most abundant protein in the body
Strong as steel
Type I Collagen
predominantly in ligaments. tendons, menisci, and joint capsules
Type II Collagen
Predominantly in hyaline articular cartilage and nucleus pulposus of disk
Elastin
Properties allow the fibers to deform under force and return to original state
Generally less elastin in connective tissue
Connective tissue composition and structure
Sparsely vascularized, parallel fibers
Dense connective tissue in tendon and ligament
Type I collagen production
Fibroblasts make procollagen which is cleaved to produce type I collagen
Coiling of connective tissue
Polypeptide chain coiled in left handed helix
Three alphas chains are then coild in a right handed helix.
Cross links
Formed by GAG’s between collagen molecules
Aid in strength
More elastin in _____ than ____
Ligaments; Tendons
Overload
Tissues increase their structural or functional capability in response to overloading
Specificity
Specific stimulus for adaptation elicits specific structural and functional changes in specific elements of tissues
Reversibility
Discontinueing training stimulus will result in loss of adaptive changes
SAID
Specific Adaptations to Imparted Demand
Elasticity
Property of a material to return to original form following removal of deforming load
Plasticity
Property of a material to deform permanently when loaded beyond its plastic range
Viscocity
Property of a material to resist loads that produce shear
Higher viscosity —–> Slower deformation
Elastic Materials
Energy is stored during loading and released during unloading
Loading/Unloading curves are the same
Visco-Elastic materials
Sensitive to rate of loading or deformation
Higher rates lead to more deformation
Creep
Load is suddenly applied then held constant
Continued deformation over time
Stress Relaxation
Deformation held constant
Force required to maintain deformation decreases over time
Cyclical Loading
Causes a shift of the load:elongation curve to the right
Shift decreases in magnitude with each repitition
Hysteresis
Energy loss
Viscoelastic behavior
Increased stiffness w/ increased strain rate
Tendon Loading
Tendon has 2x the tensile strength of muscle
Muscle rupture is more common than tendon rupture
Investing DCT
Paratenon: Outside
Epitenon: Synovial tissue only in high friction location
Endotenon: continuous with perimysium and periosteum
Sharpey’s fibers
Link tendon to bone, go into the bone
Tendon Inflammatory phase
Cellular Reaction
Tendon Collagen Synthesis
Proliferation
Tendon Remodeling
Maturation
Immobilization in tendons
Reduces water content; PG Content; and strength. Tendon softens in 1-2 weeks
Early intermittent passive mobilization
CPN machine
Ultimate load increased
Reduced adhesions
Functions of Myotendinous Junction
Adhesion
Force transmission
Force mustnt exceed strength of interface & adhesion
Muscle tendon & bone-ll-bone failure
Pre-epiphyseal closure - failure at epiphysis
Post-epiphyseal closure - failure at mtj
Avulsion less common than mid substance in adults
Stretching Connective Tissues
Mode
Intensity
Frequency
Duration
Loading effect on length of Peri-articular DCT
low load of 5-40 minutes
Mobilization doesnt effect length, but can enhance ROM
Loading effect on muscle length
30 Seconds minumum continuous duration (maintain end range)
Strength Tissue Training
3-5 sets
6-12 Reps
Muscular Endurance Training
3-5 sets
20-30 Reps
Tendon Training
3-5 sets
30-40 Reps
Ligament Training
1000s of reps
Cartilage Training
Hours of reps
Articular Cartilage Physiological Features
Avascular, aneural, low metabolism
Withstands loading, distributes load, low friction
Zone 1 of articular cartilage
Nearly horizontal fiber direction resist shear
Zone 2 of articular cartilage
Slightly diagonal fiber direction to resist some shear, some compression
Zone 3 of articular cartilage
More vertical, resist more compression
Zone 4 of articular cartilage
Vertical fiber direction resists compression
Chondrocytes
Make & secrete matrix
Electrical activity elicits a synthesis response
Unique property of AC
Fluid component. Water content decreases and PG content increases with depth of tissue
