Tissue Biomechanics Flashcards
What effect do mechanical forces have on tissues?
Important for:
Development (of tissue and damage/disease)
Maintenance
Remodeling
What is the definition of tissue biomechanics?
Study of how different parts of the human body react to external forces
What is the definition of tension?
When a structure is stretched longitudinally
What is the definition of compression?
When a load produces forces that push the material together
What is the definition of shear?
Forces acting parallel to each other in opposite directions
What is the definition of torsion?
Forces twisting/rotating in opposite directions about the long axis
What is the definition of bending?
Combination of tensile and compressive loads
What kind of a force is tension?
Stretching or pulling force
What are the tension elements of the body?
Soft tissues (fascia, muscles, ligaments, and connective tissue)
When do tensile forces occur in the intervertebral disc?
During rotational movements
What part of the intervertebral disc tends to bear the tensile loads?
Annular fibers
What is the compressive force continually being transmitted to the vertebral bodies and intervertebral discs of the spine?
Gravity
How does the structure deform during a shear injury?
Internally in an angular manner
What type of bone is most at risk for a fracture?
Cancellous bone (ex. femoral condyles and tibial plateaus)
What spinal structures are able to resist shear forces?
Facet joins and fibers of the annulus fibrosus
What areas of the spine are at risk for damage by excessive rotational force (torsion)?
Facet joint
Pars interarticularis
Capsule
Annulus
What kind of long bone fracture would be an example of a torsional load failure?
Spiral fracture
Long bone fractures frequently occur through what mechanism?
Bending (combination of compression and tension)
What are the three common tissue responses to mechanical loading?
Deformation
Growth and remodeling
Failure
What is the definition of deformation?
Local shape change under the effect of applied forces
What kind of deformation occurs when an object is subjected to external forces but is in static equilibrium?
Some local shape change within the object
What four things does the extent of deformation depend on?
Material properties
Size and shape of object
Environmental factors (ex. heat or humidity)
Force
What is the difference between the measurement of a stress or strain?
Stress - measure of the intensity of the force
Strain - measure of the degree of deformation
What is the definition of “stress” in terms of deformation?
The external force acting to deform the material
What is the definition of “strain” in terms of deformation?
Magnitude of deformation as a result of the applied stress/loading
What determines the strength of a tissue?
The maximum stress a tissue can withstand without permanent deformation
What kind of tissue strength is considered the level of stress at the yield point of a material beyond which permanent deformation will occur?
Yield strength
What kind of tissue strength is considered the maximal stress that a material can withstand prior to the initiation of failure?
Ultimate strength
What kind of tissue strength is considered the stress at which the material actually breaks or ruptures?
Failure strength
What is the definition of ductility?
Force per unit area required to deform a material, represented by the steepness (slope) of the stress/strain curve
What kind of tissues fail at low stress by can withstand a large strain (ductile/pliant or brittle/stiff)?
Ductile (pliant)
What kind of tissues can withstand high stress but fail with relatively low strain (ductile/pliant or brittle/stiff)?
Brittle (stiff)
How can the amount of “toughness” of a tissue be estimated?
Observing the total area under the stress/strain curve
What is the definition of “toughness” when referring to tissue?
The total energy required to cause material failure
What type of tissue, (bone, tendon, or ligament), is more brittle but very strong with low overall toughness?
Bone
What type of tissue, (bone, tendon, or ligament), is moderate for both strength and ductility with high overall toughness?
Tendon
What type of tissue, (bone, tendon, or ligament), is more pliant but has lower strength with moderate overall toughness?
Ligament
What is the definition of elasticity?
Ability to return to the original shape when the load is removed
What is the yield point of elasticity?
Point at which the applied stress can lead to permanent deformation
In terms of elasticity, what is the nonlinear response of the material after the yield point?
Plastic region
In terms of elasticity, once reaching the plastic region, will some degree of deformation persist after the removal of the stress?
Yes, some
What is the term for the property of materials to resist loads that produce shear or tensile forces?
Viscosity
Is the linear deformation produced by tensile stress alleviated even after the stress is removed?
No; it remains
What is another name for viscous stretch?
Plastic (putty-like behavior)
Are most soft tissues viscous or elastic?
BOTH (viscoelastic)
What affects the viscoelastic property of a material?
Both the rate of loading and the length of time that it is subjected to a constant load
What is the definition of creep?
Continued deformation over time when CONSTANTLY loaded
What is the cause of the creep in tissues?
Expulsion of water
What is the definition of relaxation in terms of viscoelastic tissue?
The corresponding eventual decrease in stress that will occur as fluid is no longer exuded
What is the definition of hysteresis?
Energy loss exhibited by viscoelastic materials when they are subjected to loading and unloading cycles
What effect does load size have on hysteresis?
Increased load = increased hysteresis
What happens to hysteresis levels when a load is applied a second time?
Decreases (less capacity to absorb the shock energy)
What is the “toe region” of a tissue?
Its normal range of motion
When does micro-failure of a tissue occur?
After taking out the slack
What kind of sprain is an example of a micro-failure?
Grade One
At the micro-failure stage, is a tissue still elastic?
Yes
What kind of stress is present when plastic deformation starts?
Yield stress
What kind of sprain is known as a macro-failure where the tissue undergoes plastic deformation?
Grade Two
What kind of sprain occurs when a tissue ruptures?
Grade Three
