Kinesiology - Tissue Mechanics
Terms
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- Function of Connective Tissue
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-Covers organs - mechanical support
-Immune Defense - Blood
-Storage of Water and Fat
-Transportation - Tissue Fluid
-Wound Healing
-Control of Metabolic Processes in Other Tissues - Componenets of Connective Tissue
- Ground Substance and Fibers (Elastin and Collagen)
- Ground Substance Components
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Extra Cellular Matrix
Proteoglycans
Glycoproteins - Function of Proteoglycans
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Hydration of Matrix
Stabilization of Collagen Networks
Resist Compressive Forces - Function of Glycoproteins
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Linkage between components
-Smaller proteins and sugars - Properties of Collagen
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-Resists tensile loads
-Tripple helix within molecule
-3 polypeptide chains folded to form a rope-like coil - Type I Collagen
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-Bones, ligaments, tendons, joint capsules
-Thick, rugged fibers gathered into bundles
-Elongate very little with tension
-Ideal for binding and supporting articulations - Type II Collagen
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-Articular Cartilage
-Thinner and Less Stiff
-Flexible woven framework for maintaining general shape and consistency of structures such as hyaline cartilage
-(Osteogenesis Imperfecta) - Connective Tissue Proper
- Loose and Dense
- Dense Connective Tissue
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-Regular - tendons and ligaments
-Irregular - Dermis of the skin - Supporting Connective Tissue
- Bone and Cartilage
- Specialized Connective Tissue
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Adipose and Hemopoietic Tissue
-Lymph and Blood - Functions of a Tendon
- Transmit Muscle Forces to Bone
- Structure of a Tendon
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-Parallel bundles of fibers between rows of fibroblasts
-Arise at the musculo-tendinous junction
-Instert on Sharpey's Fibers
(Osgood Schlatters Disease) - Functions of a Ligament
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-Stabilizes Joint
-Guides Motion
-Prevents Excessive Motion - Structure of a Ligament
- Parallel fiber arrangement with extracellular ground substance
- Tensile Strain
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-Elongation per unit length of the material in response to tensile load
-Strain=(length after load - length before load)/Length before load
-Measured in % - Tensile Stress
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Externally applied load per cross-sectional area
-Stress = F/A
-F=Externally applied distraction force
-A=Cross-sectional area of material tested
-Measured in N/mm^2 - Stress-Strain Curve Regions
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-Toe Region
-Linear or Elastic Region
-Plastic Region
-Major Failure
-Complete Failure - Linear or Elastic Region
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-Linear relationship between stress-strain
-Elongation is greater than in toe region
-Stiffness increases
-Microfracture begins
-Young's Modulus of Elasticity
-Remove Tensile force, return to pre-stressed length and shape - Young's Modulus of Elasticity
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-Steep Slope = high modulus, material is stiff or resistant to elongation
-Gradual Slope = low modulus, easily deformed (ligamentum flavum) - Rate of Loading in Elastic Region
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-Increased duration of elongation, increased time to recover to pre-stressed length
-Increase rate of loading, greater resistance to deformation - stiffness - Energy Within the Elastic Region
- -Not all energy applied is stored, some is lost as heat
- Hysteresis
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Loss of energy; difference between energy expended and energy regained
-More strain, but the same amount of force over time - Plastic Region
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-Progressive Failure - True tissue failure
-Yield point
-Slope of curve decreased
-Tissue remains permanently deformed but normal to the naked eye
-Ligamentous sprain - joint laxity or instability - Failure
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Major failure - flattening of curve
Tendon or ligament is still intact
Elongation without additional force - Complete Failure
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Ultimate stress and ultimate strain
Acute stress of more than 8% will lead to rupture - Biological Factors Affecting Biomechanical Properties of Tendons and Ligaments
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-Maturation and aging
-Hormones
-Mobilization and immobilization
-Diabetes mellitus and hemodialysis - Maturation and Aging on Tendons and Ligaments
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-During maturation, tensile strength, load to failure, elasitc modulus all improve
-With aging the tissue strength decreases - Hormones involved with tendons and ligaments
- Relaxin, Estrogen, Cortisol
- Mobilization and Immobilization with regards to Tendons and Ligaments
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-Remodel in response to mechanical demands
-Physical Training Increases Tensile Strength
-Immobilizaiton Decreases Tensile Strength, More Elongation and Less Stiff - Cartilage Types
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Hyaline and Articular
Fibrocartilage - Properties of Cartilage
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-Smooth surface for articulating bones
-Devoid of blood, lymph and nerves
-Mechanical Function - Mechanical Functions of Cartilage
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-Provides a weight bearing surface with low friction
-Helps to distribute the loads between bones - Composition of Cartilage
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-70 to 80% Water
-Proteoglycans (Protein core of Hyaluronic acid, chondroitin sulfate, keratan sulfate)
-Collagen - Type II
-Volume occupied by proteoglycan aggregates is limited by entangling collagen framework - Properties of Type II Collagen
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-Helical Proteins
-High Mechanical Strength
-Increase use, Increase diameter
-Decrease Collagen with an increase in age and immobilzation - Mechanical Properties of Cartilage
- Viscoelasticity and Creep
- Viscoelasticity
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-Mechanical behavior of a material when subjected to a constant load, its response varies with time
-Both fluid and solid-like properties
-When compressed, cartilage becomes stiffer
-(-) charged aggrecans are pushed together
-Increased repulsive force adds to stiffness - Creep
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-A viscoelastic material is subjected to a constant load over time
-Rapid initial deformation
-Slow (time-dependent) progressively increasing deformation
-Fluid flows out of the cartilage from matrix
-Permeability is highest near joint surface and lowest in deep zone - Lubrication
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Fluid Film Lubrication
Boundary Lubrication - Fluid Film Lubrication
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-Thin film of lubricant (synovial fluid) separates the bearing surfaces
-Fluid must be thicker than the roughness of the opposing surfaces
-Depends on fluid viscosity, shape of gap, surface stiffness
-Load on bearing surface is supported by pressure developed in the fluid film
-Low Loads - Boundary Lubrication
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-Joint surfaces are protected by layer of boundary lubricant
-Prevents direct contact and eliminates most surface wear
-Independent of lubricant viscosity
-Lubricin - constituent of synovial fluid responsible for boundary lubrication
-High Loads - Fibrocartilage
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-Histologically and embryologically related to articular cartilage
-Different biomechanical properties than articular cartilage
-Ex: intervertebral discs, symphysis pubis