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APK 3220c Biomechanical Basis of Movement > Tissue Loading > Flashcards

Tissue Loading Flashcards

1
Q

Force

A

𝐹 = 𝑚𝑎
a push or pull; a load that tends to produce an acceleration of a body in
the direction of its application.

Forces may:
Change a body’s state of motion or cause deformation (Strain) in the body Or Both

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2
Q

Pressure

A

force per unit area; P=F/A; distributing force over a larger area can help avoid injury; units Pa

Measures distribution of forces acting outside of a body

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3
Q

Center of Pressure (COP)

A

• Point the represents the
place of application of
the sum all forces acting
on a surface.

NOT NECESSARILY LOCATED AT POINT OF CONTACT

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4
Q

Stress

A 
distribution of force within a body,
quantified as force divided by the cross-sectional area
over which the force acts.
• “Internal” pressure
• Stress=F/A
• Normal: 10-20 N/cm2

Internal pressure; measures distribution of forces within a body

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5
Q

Strain

A

amount of deformation with respect to the structure

  • Normal (ε):ratio of the change in length (technically doesn’t have units)
  • ε = ΔL / L = (l-L)/L
  • L – original length, l=final length
  • Can be compressive or tensile
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6
Q

Center of Pressure is not the same as center of mass

A

True

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7
Q

Bending

A

asymmetric loading that
produces tension on one side of a
body’s longitudinal axis and
compression on the other side

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8
Q

Posterior Pelvic Tilt and Anterior Pelvic Tilt

A

Anterior Pelvic tilt places greater shear stress on the intervertebral discs, whereas Posterior Pelvic Tilt (neutral, lordosis of lumbar spine) places greater axial loading on the intervertebral discs. The spinal column withstands axial loading much better than shear stress.

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9
Q

Greenstick Fracture

A 
• Incomplete fracture caused
by the bending of the bone.
• The convex side ruptures
due to tensile stress.
• Failure on Tension side
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10
Q

In lumbar flexion which
area of the intervertebral
disc will undergo the
greatest compression?

A

Anterior vertebral disc will undergo greatest compression (posterior will undergo tension)

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11
Q

Torsion

A

• Load producing twisting of a body
around its longitudinal axis.
• Causes shear stress in the material

With torsion shear stress develops in the material and increases towards the periphery of the cylinder or in this case the intervertebral disc- IMPORTANT

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12
Q

Spiral Fracture

A

Oblique break due

to torsional loading.

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13
Q

Spondylolisthesis

A

anterior slippage of a superior vertebra with respect to an inferior one due to excess shear force.

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14
Q

Spondylolysis

A

Unilateral or Bilateral “scotty dog” fractures of the pars interarticularis (isthmus)

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15
Q

Most common stress felt at ligaments

A

Tensile stress

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16
Q

Most common stress felt by muscles

A

Tension

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17
Q

Most common stress felt by bones

A

Compressive Stress

18
Q

Most common stress felt at mensici

A

Compressive stress and shear stress

19
Q

Mitigating the Risk for Injury

A 
• Maintain upright posture
• Maintain a neutral spine
• Sustain intra-abdominal
pressure during lifting
• Reduce moment arm of the
load during lifting
• Avoid twisting while lifting
20
Q

Body position in order of
decreasing internal
pressure

A
  • Sitting Slouched
  • Standing Learning Forward
  • Sitting Erect
  • Standing Erect
  • Lying Flat
21
Q

Elastic materials

A
  • Elastic materials: deform instantaneously when they are subjected to externally applied loads and resume their shape when load is removed.
  • Stress is a function of strain only. No time dependent behavior
  • Materials may exhibit elastic behavior up to certain loads beyond which they will exhibit plastic behavior
22
Q

Plastic materials

A

deform instantaneously when they are subjected to
externally applied loads and do not fully recover their shape when load
is removed.

23
Q

Modulus of elasticity (E)

A

defines the slope of the linear region of the
stress/strain curve

E = Modulus of Elasticity = Young’s modulus

E = Stress/Strain

24
Q

Cortical (Compact) Bone

A

• Compact mineralized connective
tissue
• Low porosity; Stronger
• Found in the shafts of long bones
• Undergoes high level of stress without high degree of deformation/strain
• Has higher modulus of elasticity and can undergo a higher value of stress and strain elastically before deforming plastically after yield point
• More Brittle
• Cortical bone: stiffer, withstand more stress
but less strain before fracture

Accepts large loads, but can not deform much without risking fracture

25
Q

Trabecular (cancellous)/spongy bone

A 
• Less compact mineralized connective
tissue
• High porosity
• Found in vertebrae and ends of long
bones 
• Strains regularly at low loads
• Much plastic deformation before Fracture
• More Ductile
• Trabecular bone: high strain but low stress
before fracture
-deforms easily and lower stiffness
Area under the curve = energy stored in the tissue as it is deformed.
26
Q

Ductile

A

Able to yield at normal temperatures
• Large plastic deformation prior to failure
• Mechanical: steel
• Anatomical: Trabecular Bone

27
Q

Brittle

A 
Rupture occurs during elastic deformation
• Failure without undergoing plastic
deformation
• Mechanical: Cast iron, glass, stone
• Anatomical: Cortical bone
28
Q

Ductility/Brittleness of Bone and Age

A

Young Age: More ductile
Old Age: More Brittle

Load Rate (how quickly it takes to get to maximal load):
Young Age: Low Rate of Loading
Old Age: High Rate of Loading

29
Q

Bone Growth

A 
Longitudinal Growth:
• Growth at epiphyseal plate
(cartilaginous disc)
• Most fuse by age 18 ending
longitudinal growth
Circumferential Growth:
growth
• occurs throughout the lifespan
• Putting concentric layers of bone on the shaft
• Circumferential growth
• Increases bone diameter
• Occurs throughout most of
the lifespan
• Periosteum builds
concentric layers of bone.
• Bone is simultaneously
resorbed on the medullary
side.
30
Q

Epiphyseal Fracture

A 
• Damage to the growth plate area of
younger bone <18yrs.
• If hyaline cartilage is disrupted bone
growth may end.
• Can be difficult injury to treat, often
with long term effects.
31
Q

Bone Remodeling

A
  • Occurs continuously throughout life.
  • Density and shape of bone change with load. (Wolff’s law)
  • Fatigued damaged older bone is resorbed
  • Formation of new bone in response
  • About 25% of trabecular bone is remodeled yearly
32
Q

Bone Remodel- Osteocytes

A

• Osteocytes direct bone
remodeling activity
• Osteoblast deposit new bone
• Osteoclast resorb bone

33
Q

Bone Hypertrophy

A

increase in bone mass with stress

Increase in osteoblast activity

34
Q

Bone Atrophy

A

decrease in bone mass with disuse

Increase in osteoclast activity

35
Q

Buccal Exostosis

A

Extra bone buildup in the gum sockets

36
Q

Osteoporosis

A

• Bones become weak and may break from a minor fall or,
in serious cases, even from sneezing or bumping into
furniture
• Lifestyle disease that is dependent on habits
• No clear onset
• Peak bone mass during childhood is important predictor
• Weight bearing exercise in pre-puberty years may help
• Dietary Calcium (dependent on absorption via Vitamin D)

Playing field sports or participating in load-bearing exercise at a young age can help prevent this

37
Q

Anisotropy

A

• Phenomenon in which a material (i.e., bone) responds differently to different directions of loading
• Some materials act better under different
directions of load because of the microstructure
of the material

• Loading angle also matters
• More axial the load the greater ability to
withstand the load

38
Q

Wolff’s Law

A

Body will adapt to loads under which it is placed

39
Q

Composition of Bone

A
  • Minerals: calcium carbonate, calcium phosphate (60-70% dry bone weight); primarily provides compressive strength
  • Collagen: protein, cable-like (25-30% dry weight); primarily provides tensile strength
  • Water: carries nutrients to and waste away (25% of total weight) and adds to compressive strength
  • Bone is a composite material
40
Q

Stress to fracture

A

Greatest: Shear stress
Middle: Tension
Least: Compression

APK 3220c Biomechanical Basis of Movement (8 decks)

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