Properties Of Bone

Question 1

Functions of bone

Answer 1

• Protection
• Sound transmission - auditory ossicles
• Blood production in marrow
• Mineral store - calcium, phosphorus, heavy metals
• Motion and support - bones as lever arms pivoting joints as fulcrums

Question 2

Mineral phase

Answer 2

-Hydroxyapatite: carbonate and phosphate ions bound to collagen matrix

Question 3

Organic Phase

Answer 3

Collagen that acts as a scaffold and controls orientation of minerals

Question 4

Pores

Answer 4

Allow nutrients to be transported to bone and marrow cells

Question 5

Seven-fold hierarchy of bone

Answer 5

1: major components
2: mineralised collagen fibril
3: fibril array
4: fibril array patterns
5: cylindrical motifs
6: spongy vs compact bone
7: whole bone

Question 6

Three types of bone

Answer 6

• compact / cortical bone
• trabecular / cancellous bone
• woven bone

Question 7

Compact bone description

Answer 7

-hard outer layers of bone
- 5 to 15 percent porosity
- consists of Haversian canals and osteons
- 80 percent of bone in body

Question 8

Trabecular bone description

Answer 8

• open network of rod and plate-like elements allowing room for blood vessels and marrow
• adapts to changing strains
• allows for remodelling
• 20 percent of bone

Question 9

Woven bone description

Answer 9

• produced rapidly after fracture
• disorganised structure of collagen fibres
• weak
• can reorganise and turn to lamellar bone which has aligned collagen sheets and is much stronger

Question 10

Factors affecting properties of bone

Answer 10

• composition: high mineral content increases stiffness and strength, lowers toughness
• humidity: dry bone is stiffer, less tough, has lower fracture strength and lower strain to failure
• type of load: stronger in tension than compression, weak in torsion, axial elastic moduli larger than transverse moduli
• rate of loading: modulus, compressive strength, yield strength all increase with rate of loading

Question 11

Bone remodelling process - three cells involved

Answer 11

• Osteoblasts: make organic scaffold that mineralise to form new bone
• Osteocytes: maintain levels of oxygen and mineral
• Osteoclasts: travel to bone surface and unfix calcium by secreting acid phosphotase

Question 12

Wolff’s law

Answer 12

• bone remodelling responds to load applied
• this produces more bone in system and in orientation along stress lines of loading
• lack of loading can lead to thinning of bone

Question 13

Types of fracture

Answer 13

• simple (skin intact) or complex (skin broken)
• complete (fragments separate) or incomplete (partially joined)
• linear, transverse or oblique with respect to long axis of bone
• spiral fractures (part of bone twisted)
• comminuted fractures - bone broken into several parts
  - impact fractures where bone is driven into each other, avulsion where a bit of bone is separated from the rest

Question 14

Stages of healing fractures

Answer 14

<five days: clotted blood forms at site, bone cells die, fibroblasts lay scaffold for next stage
Five days-three weeks: callus of cartilage fills gaps, fibroblasts and osteoblasts migrate to start remaking bone
Three weeks-three months: bony callus forms using soft callus as scaffold - gentle loading helps bone lay more material
>three months: remodelling, woven bone becomes lamellar bone and density increases