bone mechanics

Question 1

ortho hardware

Answer 1

• screws - cortical screw, cancellous screw, polycarbonate (radiolucent) screw), differential pitches
• screw holes are oblong and the portion of each hole distant from the fracture has a shoulder
• external fixations
• plates
• tension banding
• wires
• k- wires (wires drilled into bone)

Question 2

fracture healing risks

Answer 2

1. compartment syndrome (build up fluid within muscle sheath)
2. infection.
3. unequal limb length.
4. non-union (inadequate blood supply, infections, large gaps –> callous development but no remodelling)
5. no healing after 6 months
6. loss of function plus pain

Question 3

age

Answer 3

reduced strength, increased stiffness and brittleness
increase in non-enzymatic cross linking between collagen fibres leads to difficulty sliding over which decreases plasticity of bone. This increases in osteon numbers, this prevents the bridging of microcracks and thus the strengthening of bone + reduction in energy absorption

Question 4

osteoporosis

Answer 4

disrupted trabecular structure
decrease in bone mineral density
increase E - brittleness
increased fracture risk
too much resorption too little formation

Question 5

loading rate

Answer 5

E increases with loading rate
bones adapted for strain rates during activity (absorb minimum energy)
in injury realm see fracture at lower strian rates.

Question 6

transverse fractures

Answer 6

at 90 degrees to axis

Question 7

OP risk factors

Answer 7

being a woman
menopause - decrease in estrogen, estrogen inhibits resorption (osteoclast apoptosis is regulated by estrogen) without estrogen osteoclasts live longer and resorb more bone
being thin
exercise
malnutrition
low initial peak bone mass

Question 8

OP causes

Answer 8

unclear
change in formation + resorption
change in width/centre of lazy zone

Question 9

bone mineral content

Answer 9

measured by a DEXA scan, higher density bone transmits fewer low energy X-rays

Question 10

non traumatic fracture

Answer 10

older people, weak bones

Question 11

osteoporosis treatment

Answer 11

calcium supplements
bisphosophonates - inhibit osteoclast resorption, good in short term but allows accumulation of microcracks and catastrophic bone failure.
exercise
estrogen replacement therapy

Question 12

simple fracture

Answer 12

broken in one place

Question 13

comminuted fracture

Answer 13

broken into 3 pieces or more

Question 14

oblique fracture

Answer 14

at 45 degrees to bone axis - SHEAR FAILURE

Question 15

greenstick

Answer 15

soft young bone, bending, fracture not all the way through the bone

Question 16

traumatic

Answer 16

impact injury - typically younger populations

Question 17

compression fractures

Answer 17

old people, OP, typically in vertebrae, IVD becomes wedge shapes leads to hunched over

Question 18

spiral

Answer 18

torsion fracture typically at 45 degrees to bone axis - SHEAR FAILURE

Question 19

fracture treatment stabilisation

Answer 19

casting - simple closed fracture
nails, screws, plates, wires - complex, open fractrues, displaced + comminuted.
external fixation - comminuted, limb-lengthening - adjustable but high infection risk

Question 20

endochondral ossification

Answer 20

fracture occurs, blood clot develops, osteoblasts are recruited, soft ligamentous connection forms + cartilagenous callus, then remodelling occur s