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Flashcards in Bone Deck (28)
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1
Q

A measure of resistance offered to external loads by a material as it deforms

A

Stiffness

A stiffer material needs more stress to deform.

2
Q

The amount of stress (load) over the amount of strain (deformation)

A

Stiffness

S = Load over deformation

3
Q

What are 2 ways that bone works as a shock absorber?

A
  1. End plates bow

2. Vertical columns bow

4
Q

What type of loads result in end plate or compression fractures?

A

Fall on butt
Land on heels
Lift heavy loads

E.g. Snowmobiling, Skiing, Snowboarding, Slipping on ice

5
Q

How is spinal percussion used in detecting a fracture?

A

Tap on SPs
Pt says ouch
If it’s fractured, Pt might say OUCH!!
If there’s a space occupying lesion, Pt might say OUCH!!
Lytic lesion hurts more than blastic lesion.

6
Q

What part of the bone is innervated?

A

Periosteum

7
Q

What is hemearthrosis?

A

Blood in joint. Refer out immediately.

8
Q

Shear strain is measured by the angle created by deformation. The angle is measured in:

A

Radians

9
Q

Cortical bone can withstand much __________ (less/greater) compression loads compared to tensile/tension or shear.

A

Greater

10
Q

In bone bending stress (3 point bending), what fails first: tensile or compression?

A

Tensile (the convex side)

E.g. boot top fracture while skiing ⛷

11
Q

Explain the mechanism of 3 point bending loads

A

When a bone is held in place and a compressive force is applied to one side, the tensile side (the other side) will fail first.

The compressive force is the concave side and it will fail last; the tensile side is the convex side and it fails first.

12
Q

Twisting causes shear stress around the

A

Axis

The further from the axis, the greater the shear stress

13
Q

What is torsion?

A

Combination of shear, tensile and compressive stress

14
Q

In a torsion stress, where there is shear and tension stress, what happens first, second and what does it look like?

A

First: Bone fractures along shear stress lines - vertical

Second: Bone fractures along tension stress lines - diagonal

15
Q

Bone is about ____% stronger in brisk walking than slow walking

A

30%

16
Q

What are the risks of end plate fractures (3)

A
  1. Schmorl’s nodes - nucleus pulposus migrate through cracks in end plate
  2. Loss of disc height at that level
  3. If enough disc height lost, nerve root may compromise in IVF
17
Q

UMN lesion looks like

A

Hyperreflexia

This is a contraindication for HVLA.

18
Q

Repetitive loading causes

A

Decreased strength

19
Q

When do fatigue fractures occur?

A

High repetitions, low load

20
Q

How does muscular contraction help protect bone?

A

Certain muscle groups produce compression stress that can reduce or neutralize tensile stress of bending

E.g. triceps surae resist stress on posterior tibia

21
Q

Response of cortical bone is dependent on direction of a tension stress

A

Anisotropic property

22
Q

When muscles fatigue, what is the risk for bone?

A

The muscle does not protect the bone from stress when it’s tired, so more likely to stress fracture

23
Q

What is Wolff’s law?

A

Bone is laid down or resorbed where needed.

The GREATER the body weight, the GREATER the bone mass.

E.g. bed rest = 1% bone mass lost per week

24
Q

What is the effect of aging on bone mass?

A

Women lose 1.5-2% bone mass each year from 4th decade on

Men lose at half that rate

25
Q

Define brittleness in terms of plastic deformation

A

Quality whereby a material exhibits LITTLE plastic deformation before failure

26
Q

Failure happens at

A

Less than 5%

27
Q

What is the correlation between corticosteroids and fractures?

A

1/4 people on corticosteroids will have a fracture

E.g. asthma patients who use corticosteroids less than 1 yr have increase prevalence of vertebral fractures

28
Q

What is the role of exercise in treating osteoporosis?

A

A modest reduction of bone resorption resulting in only minor reduction in bone mass density loss per year

Also exercise can reduce fracture risks by reducing frequency of falling.