Soft Tissue and Injury

Question 1

What are the 4 major types of loading

Answer 1

1) Compression - Pushing ends together
2) Tension - Pulling ends further apart
3) Torsion - Twisting
4) Bending - Lateral forces

Question 2

What is Stress?

Answer 2

The Resistive force generated inside the material per unit area

Question 3

What is longitudinal strain?

Answer 3

The linear deformation (change in length) per unit length

Question 4

What is strain?
How is it measured?

Answer 4

Change in shape or deformation of the material
Measured as a percentage (Relative Strain):

Change in Length / Original Length

Question 5

Young’s Modulus for Stiffness of Material

Answer 5

The Steeper the slope the stiffer the object
Going to the first point (point A) is a linear slope
Going to Next point –> non linear slope
Higher than the second point causes plastic deformation
Beyond plastic deformation causes the intermolecular bonds to displace beyond repair

Question 6

What is hook’s law?

Answer 6

Up to the proportional limit of a material you will get a linear response

Question 7

What is the reference point for microstrain?

Answer 7

10,000 Microstrain is 1% of the change in length

Question 8

What is Viscoelasticity and its deformation

Answer 8

Refers to Part elastic, Part fluid

Deformation of elastic material that contains fluid causes a delay in the return of the material back to its original shape

Exhibit time dependent strain (CREEP)

Question 9

Viscoelastic response to bone loading

Answer 9

Viscoelastic tissues and bone are stronger when they are loaded fast
- Due to bones being loaded under torsional strain

Question 10

Is Slow Loading of bones stiffer or weaker?

Answer 10

Less stiff.
Easier to break bones when the strain is low

Question 11

What are the 5 points on the stress-strain curve?

Answer 11

1) Proportional limit (hooks law)
2) Elastic Limit (still elastic but not maintaining hooks law)
3) Yield point (Plastic deformation occurs)
4) Ultimate stress
5) Rupture Point - fractures and breaks down

Question 12

Describe the stress or strain in the following:
a) Cortical bone
b) Cancellous Bone
c) Articular Cartilage

Answer 12

a) High amounts of stress for low amount of strain
b) Low amount of strain
c) Exhibits large amounts of strain

Question 13

What is the role of Articular Cartilage?

Answer 13

• Provides a low friction interface
• Fluid Flow in and out of the cartilage causes its extreme strain responses
• Greatly influenced by the amount of time that force is applied

Question 14

What is Creep?

Answer 14

The increase deformation under a constant load
Strain slowly creeps to a higher level over time (time dependant strain)

Question 15

What is prone to creep? Why??

Answer 15

Articular cartilage is prone to creep due to its viscoelasticity nature

Question 16

Explain Neck Ligament Creep

Answer 16

Leaning forward to look at a computer screen increases the moment arm.

Stretching the ligaments to a length by which they cannot return

Skill acquisition is required to return the structures back to the normal length

Question 17

Is static loading healthy or unhealthy for cartilage?

Answer 17

Unhealthy

The Synovial Fluid is forced out of the cartilage but not allowed to flow back into the cartilage –> no fluid flow in and out of the system

Question 18

How does synovial fluid act as dynamic force attenuator?

Answer 18

Under low rates of loading - it is not stiff –> passing the load on to the bone tissue –> causing strain to the bone tissue

Under High Rates of loading - Cartilage is stiff
Protecting the bone from harmful high frequency forces

Question 19

Fatigue Limit VS Static Failure

Answer 19

Fatigue Limit
- Stresses below the limit can be endured for an infinite number of cycles
- Overdoing it can cause injury (must be load regulated)

Static failure
- Stress required to fracture from a single application of force

Question 20

What effect does training have on the failure/non failure region?

Answer 20

Training can cause the non failure region to shift to a higher limit
- This is why we train

Detraining can cause the curve to shift lower - hence increasing the risk of injury

Question 21

Is a bone stronger under tension or compression? Why?

Answer 21

Compression

As the force is then projected longitudinally compared to a torsion or tension where the force would be from the side of the bone

Question 22

What are interventions to reduce KAM? Why would you use them

Answer 22

Lateral Foot Wedge
Valgus Knee Bracing
Toe Out Gait
Contralateral Cane

Used to reduce the length of the moment arm on the medial side of the leg. Bringing the GRF vector closer to the knee joint.

Question 23

What causes injury to occur?
(in reference to load)

Answer 23

When the mechanical load is in excess of the tissues load tolerance
Considering both intrinsic and extrinsic factors