Hard Tissue Mechanics Flashcards
What are the two types of bone tissue?
Cortical and Trabecular bone.
What are the two types of bone loading ?
Cyclically and Statically
What are the 4 types of bone ?
Long - consists of a marrow cavity within the shaft (diaphysis) and two epiphysis ends. Found in the femur/tibia.
Irregular - e.g vertebrae within the spine.
Short - examples are found within the wrist and ankle.
Flat - e.g the skull or the scapula (back)
What makes up the composition of bone tissue and how is this split in weight and in volume ?
Bone tissue is made up of organic and inorganic phases as well as water.
By weight, bone is 60% inorganic, 30% organic and 10% water.
By volume, bone is 40% inorganic, 35% organic and 25% water.
What is the inorganic phase of bone ?
An impure form of calcium phosphate known as hydroxyapatite.
It is not pure as within its crystalline structure are impurities such as potassium, magnesium and sodium or carbonate and chloride in place of other ions.
What are the 3 forces applicable to bone ?
Compression - squeeze together
Tension - pull apart
Shear - opposite directions.
What are bending and torsion ?
Torsion is a twisting as a result of multiple loads.
Bending is when one side of a material experiences compression when the other experiences tension.
An example of bending is within the femur during gait with a walking stick where the medial side of the femur experiences compression and the lateral side tension.
What are stress and strain and their equations with units ?
Stress = F/A in N/m^2 or Pascals
Strain = Change in Length/ original length and has no units.
What is stiffness (mechanical strength) and what are the regions of interest of a graph?
Stiffness = change in load/ change in deformation. Can be used synonymously with Youngs Modulus (Stress/strain).
Elastic Region - Straight line where m = stiffness.
Yield Point - the elastic limit separating the elastic and plastic regions
Plastic Region - massive deformation increases with small load changes.
How do the regions link to hard tissue ?
Hard tissue is never fully elastic as it always loses some energy as a result of a reaction.
When a hard tissue is within the plastic region, deformations occur at the microstructural level.
What is mechanical strength ?
Maximum force or total energy the material can absorb before failure. Total energy is equal to the area under the graph.
What parts of the graph would medical experts be interested in ?
Conditioning/ Rehab - Yield Point
Sports Doctors - Mechanical Strength
What is the formula for strain energy and how does it link to anatomy ?
E = 1/2 * k* x^2
Tendons and Ligaments are elastic structures to store strain energy.
What is a viscoelastic material in relation to loading ?
The rate of loading effects the stress and strain felt by the material.
Tendons and other bio tissue is an example of viscoelasticity.
What part of the graph is much of the tendon loading found ?
The toe of the graph (where there is less than 5% strain) is responsible for most of tendon loading.
