Biomechanics / Biomaterials

Question 1

Importance of bone

Answer 1

Load-bearing
Protection
Support
Ca/phosphorus homeostasis
Endocrine processes

Question 2

Mechanics

Answer 2

Effects of forces acting on bodies or structures

Question 3

Biomechanics

Answer 3

Application of mechanics in biological systems

Question 4

Stress

Answer 4

Calculated quantity of internal interactions between adjacent constituent elements

The force applied - cannot be measured (measurable are loads/deformation)

Only a POINT (despite units of N/m2)

Question 5

Strain

Answer 5

Measure of deformation of a material in response to stress

Proportional difference between loaded/unloaded state

Strain = change in length/length

Question 6

Strength

Answer 6

Ultimate load a materials an withstand before catastrophic failure

Question 7

Stiffness

Answer 7

Rate at which a material deforms when load is applied

Question 8

Elastic deformation

Answer 8

Temporary shape change, self-revering

Question 9

Yield point

Answer 9

Transition point between elastic and plastic deformation

Question 10

Plastic deformation

Answer 10

Permanent distortion; original form cannot be regained without force

Question 11

Failure point

Answer 11

Breaking point

Question 12

Viscoelastic

Answer 12

Strength that depends on rate that loaded

I.e. stronger when loaded rapidly

Question 13

Anisotropic

Answer 13

Mechanical properties dependent on direction of loading

I.e. stronger along long-axis

Question 14

Toe region

Answer 14

Prior to elastic region

Question 15

Toughness

Answer 15

Area under stress-strain curve

Question 16

Resilience

Answer 16

Area under linear region of stress-strain curve

Question 17

Stiffness

Answer 17

Slope of load deformation curve

Question 18

Cortical bone

Answer 18

5-10% porosity
Brittle (short plastic deformation phase)
Viscoelastic + anisotropic

Question 19

Cancellous bone

Answer 19

75-95% porosity
Weaker / more compliant than cortical bone
Short elastic phase, lower yield, lower stiffness
Very long plastic phase

Question 20

Bone modeling

Answer 20

Stimulated by changes in local soft tissue strain

Inc strain —> new bone matrix
Dec strain —> resorptive remodeling

Question 21

Wolff’s law

Answer 21

Bone forms in areas of high stress and not in areas of little stress (i.e. need to stress bone to help growth in remodeling phase)

Question 22

Axial force

Answer 22

Parallel to long axis of bone

Tensile forces - lengthen
Compressive forces - shorten

Question 23

Shearing force

Answer 23

parallel or tangential to face of a material

Question 24

Torsional force

Answer 24

Twist about long axis, creates shear stress

Question 25

Binding force

Answer 25

Convex on one side, concave on other

Question 26

Fracture due to axial force

Answer 26

Oblique

Question 27

Fracture due to bending force

Answer 27

Transverse

Question 28

Fracture due to bending + axial force

Answer 28

Butterfly fragment

Question 29

Fracture due to torsion

Answer 29

Spiral

Question 30

Strain theory of bone healing

Answer 30

Bone needs strain <2% to heal Small fracture gap —> higher strain Large fracture gap —> lower strain Strain = change in length / length

Question 31

Tissue viability by strain tolerance

Answer 31

Granulation tissue - 100% strain Cartilage cell - 10% strain Bone cell - 2% strain

Question 32

Body decreases interfragmentary strain via

Answer 32

Fracture resorption Periosteal callus formation

Question 33

Biomaterials

Answer 33

metals (316L stainless steal, Co-Cr-Mo alloy, Ti+alloys, nitinol) Polymers (ultra-high MW PE; PMMA)