Soft Tissue and Injury Flashcards
What are the 4 major types of loading
1) Compression - Pushing ends together
2) Tension - Pulling ends further apart
3) Torsion - Twisting
4) Bending - Lateral forces
What is Stress?
The Resistive force generated inside the material per unit area
What is longitudinal strain?
The linear deformation (change in length) per unit length
What is strain?
How is it measured?
Change in shape or deformation of the material
Measured as a percentage (Relative Strain):
Change in Length / Original Length
Young’s Modulus for Stiffness of Material
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
What is hook’s law?
Up to the proportional limit of a material you will get a linear response
What is the reference point for microstrain?
10,000 Microstrain is 1% of the change in length
What is Viscoelasticity and its deformation
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)
Viscoelastic response to bone loading
Viscoelastic tissues and bone are stronger when they are loaded fast
- Due to bones being loaded under torsional strain
Is Slow Loading of bones stiffer or weaker?
Less stiff.
Easier to break bones when the strain is low
What are the 5 points on the stress-strain curve?
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
Describe the stress or strain in the following:
a) Cortical bone
b) Cancellous Bone
c) Articular Cartilage
a) High amounts of stress for low amount of strain
b) Low amount of strain
c) Exhibits large amounts of strain
What is the role of Articular Cartilage?
- 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
What is Creep?
The increase deformation under a constant load
Strain slowly creeps to a higher level over time (time dependant strain)
What is prone to creep? Why??
Articular cartilage is prone to creep due to its viscoelasticity nature
Explain Neck Ligament Creep
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
Is static loading healthy or unhealthy for cartilage?
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
How does synovial fluid act as dynamic force attenuator?
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
Fatigue Limit VS Static Failure
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
What effect does training have on the failure/non failure region?
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
Is a bone stronger under tension or compression? Why?
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
What are interventions to reduce KAM? Why would you use them
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.
What causes injury to occur?
(in reference to load)
When the mechanical load is in excess of the tissues load tolerance
Considering both intrinsic and extrinsic factors