Week 3 Flashcards
Sprains, Strains, Dislocations; Back Pain (39 cards)
What is Stress
stress is the internal force divided by the cross- sectional area of the surface, on which the internal force acts.
Stress= Froce/ Area
Stress= N/m^2
Mechanical Stress
As area increases, stress decreases
as the area decreases, stress increases
what are the types of mechanical stress
- Unloaded
- Tension
- Compression
- Bending
- Shear
- Torsion
- Combined loading
Tension
- acts perpendicular to the long axis of a structure
- the larger the cross-sectional area the smaller the stress
- an object deforms by stretching or elongating
- bones, tendons, ligaments
Compression
- load tends to push or squash molecules of a material more tightly together
- an object deforms by shortening in the direction of the external force
- bones, cartilage
Shear and Torsion Stress
Shear: transverse stress that acts parallel to the analysis plane
Torsion: twisting in opposite directions
The object tends to deform by changing in orientation of the sides of he object ( skewing)
-Bones, cartilage
Bending
- Tensile stress - on one side and compressive- on the other
- the greater depth= the greater bending loads can be tolerated
- a long bone (a beam ) deforms by curving (one side elongates while the other - shortens)
-bone, cartilage
Strain
strain is the quantification ( relative measure) of the deformation of a material
strength is
to do with teh max stress (or strain) the material is able to withstand before failure
material properties- stress/strain
- The amount of deformation a materail undergoes under stress determines its material properties
- Plotting stress and strain together as a stress-strain curve tells you a material’s properties such as elasticity/stiffness (young’s modulus) and strength
- Different materials will behave differently to each other. Bone=stiff while tendon=elastic
- Materials often behave differently under different loading conditions
viscoelasticity
Biologicla tissues are :
- Structurally complex
- Anisotropic- mechanical strength properties are different for each major direction of loading
- Nature of protein fibers and amount of calcification determine the mechanical response
- CT of muscles, tendons, and ligaments have additional region ( toe region) in their load deformation graph due to the straightening of the waves on the collagen fibres
- Biological tissues like tendons and ligaments are not perfectly elastic
- Viscoelasticity = stress and strain in the tissue is dependent on the rate of loading
- As speed increases , stiffness increases
- Change of speed = change of slope of curve
Properties of Viscoelastic Tissue
- Creep: gardual elongation (increasing starin) of a material over time when placed under constant tensile stress
- Stress relaxation: decrease in stress over time when a material is elongated to a set length
- Hysteresis: different unloading response than loading response i.e. loss of energy due to tissue not being perfectly elastic
What does viscoelasticity mean for exercise and injury prevention?
Stretching exercises should be done slowly to minimise force increases in muscle-tendon unit
Long-held or repetitive work postures that stretch ligaments, reduce their mechanical and proprioceptive effectiveness, increase laxity, and the risk of injury
Ligaments
- Attach bone to bone
- Hold skeleton together
- Withstand tensile stress maintain opposition of articular surfaces
- Prevent excessive motion
- Static restraint
- Transmit forces for movement production
- Proprioception
Tendon
- Attach muscle to bone
- Withstand tensile stress
- Transmit forces for movement production
- Dynamic restraint
- Proprioception
- Fixed to bone by enthesis
- Fixed to muscle by the myotendinous junction
Connective Tissue constitutes of
- Cells = 20% such as fibroblast
- Ground substance Fibers: such as collagen fibre for strength, elastic fibre for flexibility, and reticular fiber for mass
Dense connective tissue
ligaments and tendons include collagen 70-80% and 3-5% of elastin fibres of dry weight
Properties of tendons and ligaments
primarily parallel collagen fibres
fibres are slightly wavy or crimped
few elastic fibres
they are stiff and high in tensile strength while retain flexibility
have little resistance to compression and shear
aniosotropic material
elastic material
viscous material
‘creep’ phenomenon (time dependent elongation of tissue under constant stress)
ligaments have more elastin (weaker than tendons and better with non-axial loads)
Thicker tendon
- Greater cross-sectional area
- The larger loads can be applied prior to failure
- Increased tissue strength
- Increased stiffness
Longer tendon
- Greater elongation prior to failure
- Decreased tissue stiffness
- Unaltered tissue strength
Musculoskeletal injuries include
- fractures
- joint dislocations
- ligament sprains
- muscle strains
Musculoskeletal injuries long term complications
- instability
- stiffness and impaired ROM
- nonunion or malunion
- osteonecrosis
- osteoarthritis
Musculoskeletal injuries acute complications
- bleeding
- nerve injury
- fat embolism
- compartment syndrome
- infections
Strain
is a stretching or tearing of muscle or tendon
1st degree: minimal (fibers are stretched but intact, or only a few fibres are torn)
2nd degree: partial ( some to almost all fibres are torn)
3rd degree: complete (all fibres are torn)
