BioMech 3

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  1. injury is the result of:
    tissue micro/macro failure under a load
  2. load:
    amount of force on an object
  3. tensile load
    pulling apart
  4. compressive load
    pushing together
  5. shear load
  6. stress:
    • load/crosssectional area
    • newton/meters
  7. deformation
    a change in length in response to a load
  8. strain
    deformation/original length
  9. tensile and compressive strain is measured in:
  10. shear strain is measured in
  11. elasticity
    no loss of energy, tissue returns to original length
  12. plasticity
    loss of energy, permenent deformation
  13. stiffness
    • amount of stress/amount of strain
    • resistance during deformation
  14. flexibility
    • amount of strain/amount of stress
    • compliance during deformation
    • muscles>ligs>tendons
  15. brittleness
    • failure <5%
    • little plastic deformation before failure
  16. ductility
    • failure >5%
    • lots of plastic deformation
  17. viscoelasticity
    • materials deformation depends on rate, speed, quality, and duration of loading
    • links deformation to load
  18. creep
    deformation of a tissue over time with a constant load
  19. fatigue
    repeated loading causing plastic deformation and failure (bending a paper clip)
  20. relaxation
    less load needed to maintain a deformation (stretching)
  21. hysteresis
    loss of energy from a load even when the tissue returns to its original length
  22. damping
    • resistance to the speed of loading
    • fast load= more resistance
    • slow load= less resistance
  23. thixotrophy
    reduction in fluid viscosity after movement (ketchup)
  24. enthesis
    bone-tendon/ bone-lig complex
  25. enthesiopathy
    lig pulling on bone (pump bump, Osgood-Schlatters)
  26. ligs and tendons are made of:
    • collagen and elastin fibers
    • reticular fibers
    • ground substance
    • cells
  27. lig and tendon behavior depends on:
    • number of collagen vs number of elastin fibers
    • properties of fibers
    • fiber orientation
  28. lig and tendon strength depends on:
    • fiber composition
    • size and shape
    • orientation
  29. are ligs or tendons stronger? why?
    tendons. more parallel collagen fibers
  30. both tendons and ligs are strong under normal conditions but:
    • repetative loads (micro)
    • sustained loads (micro)
    • heavy loads (macro)
  31. steps in collagen fiber loading
    • 1. take out the slack, straighten out fibers
    • 2. resistance/stiffness
    • 3. ductile, withstands 6-8% strain
  32. steps in elastin fiber loading
    • 1. flexible (200%)
    • 2. suddenly stiff
    • 3. brittle= failure!
  33. function of ligs
    • stabilize joints
    • guide motion
    • prevent excessive motion
    • detect weight and direction of a load
    • detect tissue damage
  34. 1st region in stress/strain curve
    Toe region- taking out slack
  35. 2nd region in stress/strain curve
    elastic region- stretch, returns to original length
  36. 3rd region in stress/strain curve
    plastic deformation- tearing and deformation
  37. ultimate failure point:
    point of maximum strength, then large or complete loss of energy
  38. lig flavumm stress/strain curve
    • long elastic range then sudden failure
    • 2/3 elastin fibers
    • absorbs shock
    • protective
  39. ACL stress/strain curve
    • toe- straightens out. anterior drawer test
    • elastic- beginning of injury, Grade 1 sprain, microfailure
    • plastic- grade 1 sprain, pain, instability
    • plastic- gross failure (6-8%), partial rupture, joint instability, 50% decrease in strength, severe pain and swelling
    • complete failure- grade 3 sprain, complete rupture, instability, dislocation, severe pain, then less pain, then none...weird
  40. residual effects of severe sprains:
    • hypermobility and instability
    • joint degeneration
    • suscveptability to furthur injury
  41. loading speed and injury
    degree of injury depends on rate and magnatude of loading
  42. high speed loading causing:
    tears 2/3 of the time
  43. low speed loading causes:
    avulsion fracture
  44. why does the lig give with fast loading?
    both bone and lig strengthen but bone strengthens faster so lig fails
  45. remodeling/healing
    • increased stress/movement causes stronger and stiffer lig/tendon...good thing!
    • decreased stress/movement causes weaker lig/tendon
  46. monkey test
    8 week imobilization, after 1 year of rehab, still not 100% normal
  47. effects of aging on ligs
    • loss of strength
    • loss of stiffness
    • loss of energy storage capacity
  48. sustained loads and ligs
    • creep and hysteresis start in 20 minutes
    • creep and relaxation set in in first 6-8 hours
    • hysteresis lasts 1-2 hours
  49. repetative stress and ligs
    less external load needed to cause tissue failure
  50. repetative stress causes failure at what percent strain?
  51. hysteresis curve
    • change in length= set
    • area under the curve= energy lost
  52. tendon function
    attach muscle to bone
  53. composition of tendons
    almost 100% collagen w/more parallel alignment
  54. tendonosis
    • chronic
    • loss of fiber orientation
    • local necrosis and NO inflammation
  55. tendonitis
  56. stress on tendons
    depends on size of muscles and tendon and if the muscle is contracting
  57. will a muscle contraction cause a tendon to rupture??
  58. why do ligs and tendons heal slowly
    poor vascularization
  59. compression fractures are usually stable or unstable?
  60. function of bone with sudden compression
    • shock absorbers
    • end plates and vertical columns bow
  61. compression fracture
    • oblique fracture of osteons in cortex
    • 5% loss of height
    • structure shortens and widens
    • can cause schmorl's nodes
  62. most common site of compression fracture
    TL junction
  63. Bone behavior under compressive loads
    • 1. fracture- compression or end plate
    • 2. deformation w/o fracture- osteomalacia
  64. cause of compression fractures
    • fall on butt
    • land on heels
    • lift heavy load
  65. spinal percussion is good for:
    • tumor or fractures
    • would elicit deep, achy pain
  66. game keepers thumb
    • abduction and extension
    • sprains ulnar collateral lig
    • may cause avulsion
  67. bone and tension
    • failure mechanism: separation of osteons
    • ansiotrophic
    • lengthens and narrows
    • avulsion
  68. the human femur is strongest with what type of stress:
  69. the human femur is weakes with what type of stress
    horizontal tensile
  70. bone and shear stress
    • unstable fractures
    • always occur with compressive/twisting loads
    • the shear strain/deformation= angle created
  71. how does cortical bone handle different types of stress
    compression> tensile> shear
  72. bone and 3 point bending
    fractures on convex side because compressive load in front vs tensile load in back....tensile load gives first!
Card Set
BioMech 3
BioMech 3- Test 1
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