Biomechanics of Bone 1

Question 1

bone adaptation

Answer 1

there is a compensatory change on structure to offset the reduction in bone strength – adaptation

Question 2

fatigue

Answer 2

repeatedly loading a material or structure

Question 3

bone anisotropic

Answer 3

bones will fail at different stresses depending on the direction of loading (and the speed of loading as seen previously)

Question 4

strain rate

Answer 4

Bone properties are also strain rate dependant…..becoming more brittle, but stronger as rates of loading increase (more ductile at lower rates of loading)

Question 5

Bone matrix

Inorganic component

Answer 5

• Bone tissue comprises about 65% hydroxyapatite - Ca10(PO4)6(OH)2
• Stores/contains 99% of the body’s calcium (1 - 2 kg; most abundant mineral in the body)
• Bone brittleness, compressive strength

Question 6

Organic component

Answer 6

• Bone tissue comprises roughly 33% collagen (gives tensile properties)
• Bone flexibility, ductility
• Bone tensile properties

Question 7

Organisation of Bone

Answer 7

The combination of organic and inorganic components produces a material that has beneficial properties of both, much like reinforced concrete.
Lamellar bone is just like trabecular bone at the compositional level.

have dense, lamellar or cortical bone (stiffness)
or spongy, trabecular or cancellous bone (toughness)

Question 8

cortical bone

Answer 8

Cortical bone has a high value of E, small plastic region, high strength and density compared to trabecular bone.
better for lever as high modulus of Elasticity therefore less bend.

Question 9

How is bone matrix maintained?

Answer 9

osteoblasts: create bone matrix
Osteocytes:maintain bone matrix
Osteoclasts: breakdown bone matrix (multinucleated and bigger than osteoblasts)

Bone cells account for 2% of bone, the rest is matrix.

Question 10

Bone microstructure

Answer 10

Secondary osteons (= Haversian systems) formed as replacement bone within primary bone
 Microstructure is variable and complex, but may influence mechanical properties

Question 11

Bone microstructure - parathyroid

Answer 11

Chief-cells of parathyroid: polypeptide hormone: enhances Ca2+ release from bone: PTH indirectly stimulates osteoclast activity (via increasing osteoblast expression of ↑RANKL and ↓OPG)
* effects osteoclasts and stimulates osteoblasts

Question 12

Bone microstructure - calcitonin

Answer 12

C-cells of thyroid: linear polypeptide hormone: inhibits Ca2+ absorption in the intestines, renal tubular cell resorption and osteoclast activity. (anti-osteoporosis effect)