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Orthopaedic Biomechanics > Bone > Flashcards

Bone Flashcards

1
Q

Functions of bone (5)

A 
Support load
Attachment site for muscles
Protect organs (e.g. thoracic organs)
Contains haematopoietic stem cells
Calcium store
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2
Q

Composition of bone (% inorganic and organic)

A

65% Inorganic (Calcium hydroxyapatite)

35% Organic (Osteocytes, Protein matrix, Proteoglycans)

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3
Q

What mechanical properties do the inorganic & organic components of bone confer

A

Inorganic: Compressive strength
Organic: Tensile strength (collagen is like a rope)

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4
Q

What is the predominant collagen in bone

A

95% Collagen Type 1

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5
Q

What % of cortical bone is calcified

A

80-90%

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6
Q

What % of cancellous bone is calcified

A

15-25%

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7
Q

What are the 5 classes of bone

A

Flat bones: Scapulae, Sternum, Clavicle, Ribs, Skull, Pelvis
Long bones: Bones of the limbs
Irregular bone: Vertebrae, Sacrum & Coccyx, Base of skull
Short bones: Ossicles, Carpal & Tarsal bones
Sesamoid bones: Patella

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8
Q

What are the smallest functional units of cortical/lamellar bone?

A

Osteons

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9
Q

What are cement lines

A

The interface between the osteons and extra-osteonal bone matrix

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10
Q

What is the significance of cement lines

A

they are areas of low mineralisation - fractures/cracks may propagate along these lines

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11
Q

What 3 cells are in the Bone modelling Unit (BMU)

A

Osteoblasts
Osteoclasts
Bone lining cells (stem cells found on endosteum)

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12
Q

Recall the order of events in bone remodelling

A

After sensing damage, BLCs recruit ostoeclasts
Osteoclasts resorb bone
Osteoclasts die by apoptosis
BLC differentiate to Osteoblasts and secrete osteoid
Mineralisation
Maturation

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13
Q

Factors affecting mechanical properties of bone: Loading rate (3)

A

Increasing the loading rate increases the Youngs Modulus of bone –> bone is stiffer
Bone becomes more brittle –> More likely to see brittle failure
More energy is absorbed by bone

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14
Q

Factors affecting mechanical properties of bone: Loading orientation

A

Bone is anisotropic meaning that the stress response is dependent on the orientation of loading
Higher ultimate strength in Compression than tension, shear is lowest
Higher ultimate strength in Longitudinal than transverse

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15
Q

Factors affecting mechanical properties of bone: Age

A

Less stiff (lower E)
Less strong (lower ultimate stress)
More brittle
All increase fracture risk

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16
Q

Factors affecting cortical bone adaptation

A

Magnitude of loading
Frequency of loading
Number of loading cycles

17
Q

Features that change in trabecular adaptation

A

Number
Spacing
Orientation
Thickness

18
Q

Types of fracture (6)

A 
Simple: only 2 fragments 
Comminuted: more than 2 fragments
Open/compound: perforates the skin
Closed: does not perforate skin
Compression
Displaced
19
Q

Types of simple fracture (4)

A

Transverse: perpendicular to long bone axis
Oblique: fracture at an angle (usu. 45) to long bone axis
Spiral: fracture line is spiral/torsional
Greenstick: fracture doesn’t go all the way through the bone

20
Q

Factors affecting mechanical properties: Creep

A

Bone is viscoplastic
Loading bone causes irreversible/plastic change (bonds break between collagen molecules)
Next time it is loaded, its material properties vary

21
Q

Causes of fractures (2)

A

Traumatic

Non-traumatic

22
Q

How does cortical bone sense loading to adapt to it

A

Change in stress
Change in strain - osteocytes are attached to stiff matrix, loads strains stretch receptors on cells
Change in fluid flow in canaliculi

23
Q

Steps in fracture healing

A

Haematoma formations
Inflammation
Fibroblasts & Chondrocytes infiltrate and release fibrous tissue and collagen type 2 to form a soft callus
Callus is mineralised to form hard/bony callus
Bony callus is replaced by bone material - osteoblasts secrete protein matrix and mineralise
Remodelling

24
Q

Complications of fracture healing (4)

A

Non-union
Unequal limb length
Infection
Compartment syndrome

Orthopaedic Biomechanics (15 decks)

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