Lesson 10: tissue level Flashcards
the mechanics of materials of human connective tissue: bones, ligaments, cartilage, tendons, muscle
tissue mechanics
an externally applied force
Load
how an object responds to a load is determined by (7)
magnitude, location, direction, duration, frequency, variability, rate
types of axial loading
compression and tension
a load that squeezes the parts of a body together
compression
a load that pulls the parts of a body apart
tension
a load applied perpendicular to the longitudinal axis of a body causing it to curve (combination of tension on long side, and compression on the shorter side.)
bending
what 3 factors determine the effect of bending of a body
- cross sectional area
- distribution of the material around the neutral axis
- length of the body
a measure of a body’s resistance to bending
area moment of inertia
a load that causes one part of a body to move PARALLEL past another part
Shear loading
forces are directed towards each other like in compression, just not along the same line
shear loading
a type of loading that exist when there is a twist around a neutral axis
torsion
tells you how the material that makes up the body responds to loading
- internal responses of a body to a load
(stress, strain, elastic modulus, strain energy density)
material properties
tells you how a body as a whole responds to a load ( strength, deformation, stiffness, toughness)
mechanical properties
the amount of loading an object can withstand before failure
strength
a change in dimensions of a body
deformation
axial load deformation is determined as
change in length
a characterization of an object that can undergo very small deformations
brittle
a characterization of an object that can under go veery large deformations
ductile
types of deformaion
elastic and plastic
a deformation in which the object returns to its original dimensions
elastic
a deformation in which the object does not return to its original dimensions after the deformation
plastic
the amount of deformation that marks the transition from elastic to plastic deformations
- deformation beyond this point results in permanent deformation
yield point
the ration of change in load to the change in deformation (load/deformation)
stiffness
the ratio of change in deformation to change in load (deformation/load)
compliance
the amount of energy that can be absorbed by a body before failure
toughness
the amount of energy absorbed by the body as a result of deformation
strain energy
the way a force is distributed within a body
stress
the change in dimension normalized to the original dimension
strain
the ratio of stress to strain
elastic modulus (aka Young’s modulus)
relative amount of energy stored by the material
strain energy density
a DECREASE in STRESS when STRAIN is held CONSTANT for a given period of time
stress relaxation
an INCREASE in STRAIN when the STRESS is held CONSTANT for a period of time
creep
the lubricating fluid prevents direct surface-to-surface contact
boundary lubrication
movement increases the amount of fluid between articulating surfaces, thus increasing their separation
fluid flim lubrication
surface material is deformed and removed by frictional forces
wear
wear that occurs when two surfaces come in direct contact (acute)
interfacial wear
sticking together
adhesion wear
sliding past one another
abrasion wear
wear that is the result of micro-damage (chronic)
fatigue wear
a breaking apart of material
- maximum stress exceeds the ultimate stress
- strain exceeds the maximum strain
material failure
steps to create the model of injury:
- failure tolerance
- actual stress
- margin of safety
the stress level above which failure will occure
failure tolerance
how much stress the body is subjected
actual stress
the difference b/w the failure tolerance and the actual stress applied to the body
margin of safety
we want to ______ margin of safety to decrease injury risk
increase
- a injury that happens immediately
- a single external load creates enough stress that it exceeds the failure tolerance of the tissue
acute
an injury that develops over time
chronic
example of acute injury
sprains and strains
examples of chronic injury
stress fractures, anything ending in “itis”, shin splints
- outer layer of bone
- solid and dense
- aka compact
cortical
- inner layer of bone
- less organized and random
- aka spongy or cancellous
trabecular
the total amount of mineral in bone
bone mineral content
the mineral content in an area or volume of bone
bone mineral density
its not just increasing the bone mineral density, but _________________ that determines the overall strength of the bone
where the bone is placed
- exhibiting different properties when measured in different directions
- allows for stiffness and brittleness
anisotropic
the mechanics that result in an injury
mechanopathology
the braking of a bone
fracture
two types of fractures:
- acute(traumatic):occurs instantly
- stress: occurs over time
lower than normal bone mineral density
osteopenia
severe decrease in bone mineral density
osteoporosis
age and disuse have an ________ relationship with bone health
inverse
weight bearing exercise has a ________ relationship with bone health
direct
What are the three types of cartilage?
- articular
- fibrocartilage
- elastic
covers the articular surface of bones
articular cartilage
has specialized roles. ex: intervertebral discs
fibrocartilage
found in the external ear, parts of the nose, and other places
elastic cartilage
what are the two important functions of articular cartilage?
- distribute the load transmitted across the joint (decreases the stress on the joint surfaces)
- allows for relative movement of the two opposing joint surfaces with minimal wear and tear (decreases the friction)
articular cartilage is primarily loaded under_______
compression
lubricates the joints and is permeable
articular cartilage
the progressive degeneration of the articular cartilage and the bone deep to it
osteoarthritis
risk factors of osteoarthritis
aging weakness obesity malalignment injury
_________ loading brings the desired changes of increased thickness and proteoglycan content, and decreased removal
moderate, repetitive
ligaments (3)
- connect bone to bone
- restrict certain movements
- guide certain movements
ligaments are generally loaded under_____
tension
an injury to a ligament that occurs when it is stretched beyond its capacity
- usually occurs when ligament is forcibly wrapped around part of a bone
sprain
long periods of immobilization or aging lead to decrease in ______, _______, and _______ of ligaments
mass, strength, and stiffness
