Bone

Question 1

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

Answer 1

Stiffness

A stiffer material needs more stress to deform.

Question 2

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

Answer 2

Stiffness

S = Load over deformation

Question 3

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

Answer 3

1. End plates bow

2. Vertical columns bow

Question 4

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

Answer 4

Fall on butt
Land on heels
Lift heavy loads

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

Question 5

How is spinal percussion used in detecting a fracture?

Answer 5

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.

Question 6

What part of the bone is innervated?

Answer 6

Periosteum

Question 7

What is hemearthrosis?

Answer 7

Blood in joint. Refer out immediately.

Question 8

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

Answer 8

Radians

Question 9

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

Answer 9

Greater

Question 10

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

Answer 10

Tensile (the convex side)

E.g. boot top fracture while skiing ⛷

Question 11

Explain the mechanism of 3 point bending loads

Answer 11

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.

Question 12

Twisting causes shear stress around the

Answer 12

Axis

The further from the axis, the greater the shear stress

Question 13

What is torsion?

Answer 13

Combination of shear, tensile and compressive stress

Question 14

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

Answer 14

First: Bone fractures along shear stress lines - vertical

Second: Bone fractures along tension stress lines - diagonal

Question 15

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

Answer 15

30%

Question 16

What are the risks of end plate fractures (3)

Answer 16

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

Question 17

UMN lesion looks like

Answer 17

Hyperreflexia

This is a contraindication for HVLA.

Question 18

Repetitive loading causes

Answer 18

Decreased strength

Question 19

When do fatigue fractures occur?

Answer 19

High repetitions, low load

Question 20

How does muscular contraction help protect bone?

Answer 20

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

E.g. triceps surae resist stress on posterior tibia

Question 21

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

Answer 21

Anisotropic property

Question 22

When muscles fatigue, what is the risk for bone?

Answer 22

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

Question 23

What is Wolff’s law?

Answer 23

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

Question 24

What is the effect of aging on bone mass?

Answer 24

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

Men lose at half that rate

Question 25

Define brittleness in terms of plastic deformation

Answer 25

Quality whereby a material exhibits LITTLE plastic deformation before failure

Question 26

Failure happens at

Answer 26

Less than 5%

Question 27

What is the correlation between corticosteroids and fractures?

Answer 27

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

Question 28

What is the role of exercise in treating osteoporosis?

Answer 28

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.