Bone Flashcards
Bone is composed of
Osteoid (30%), Mineral (50%) and Water (20%)
Composition and function of osteiod
Predominantly collagen I; adds flexibility to rigid bone tissue
Composition and function of mineral
Hydroxyapatite (carbonated); stiffness, rigidity and strength
As time goes on, what happens to crystal structure of the bone
Crystals become less perfect (insert interstitial atoms), collagen begins to cross link which increases the bone stiffness; This cross linking can be reducible and non reducible.
The two types of bone tissue are
Cortical and Trabecular
The location cortical bone is
The shafts of lone bones, external shell of trabecular bone areas
Function of water
Provides nutrients and oxygen
The location of trabecular bone is
At the ends of long bones; at the centers of flat bones
Does trabecular or cortical bone degrade first?
Trabecular due to fragility
The function of cortical bone is to
Resist high loading
The function of trabecular bone is to
Distribute high stress
Flat bones are formed by
Direct bone formation on the fibrous scaffold
Long bones are formed by
Endochondral ossification; made on a cartilage precursor
Fracture healing works by
Cartilage formation and then replacement by bone
The bone cell types are
- Osteoclasts (OCs)
- Osteoblasts (OB’s)
- Osteocytes
The function of osteoclasts is
Resorb bone
The function of osteoblasts is
Lay down new bone (osteoid)
The function of osteocytes is
These are just OB’s locked in their matrix; they sense force due to damage and send OB’s to make OCs; OCs will remodel the bone damage away, and OBs will refill it.
Osteocytes and their processes reside in the
Lacunae and canaliculi
Bone disease is a result of
An alteration of the bone regeneration process
0th level bone element and size
Tissue; >3mm
1st level bone element and size
Osteon, plexiform bone, intersticial bone; 100-300 micrometers
2nd level bone element and size
Lamellae, canaliculi, lacunae, cement lines; 3-20 micrometers
3rd level bone element and size
Collagen fibrils, mineral crystals; 60-600nm
A lamellae is
The concentric layer(s) around a blood vessel in cortical bone
Parameters affecting stiffness of cortical bone
- Density of collagen x links
- Mineral content
- Porosity
- Tissue age
- Crystal perfection
To determine the mineral content of bone you
- micro CT or
- Ash weight (you burn the bone)
Voight model of bone
Applies a compression load on bone; bone model is alternating strips of bone and air parallel to the load; strain is equal in every portion; gives us the maximum stiffness as we vary porosity
What way do we determine the porosity affect on bone
Voight model (max affect) and Reuss Model (min affect)
Reuss model of bone
Applies a compression load; bone model is alternating strips of bone and air normal to the load; stress is the same in each section; gives us the minimum stiffness as we vary porosity
To calculate the effective contributions of individual constituents to the stiffness we need to use
The strain localization matrix, combined with the stiffness matrix of each component and the distribution of each component (volume fractions of mineral, collagen and carbonate)
The unit of trabecular bone remodeling is
The trabecular packet
When trabecular bone is remodeled it has what structure
A lamallar structure, laid down in layers (trabecular struts) that can be plate like or rod like
Parameters that might affect tissue-level stiffness of trabecular bone
- # of trabecular packets per # of struts
- Porosity (~50%), Cortical is ~10%
- Anisotropy - material =/= mechanical anisotropy
Degree of anisotropy is
1 - length of small axis/length of large axis; determined by the eigenvalues of the fabric tensor
The strain localization matrix [m] is used to
Integrate material properties into the constitutive equation; these are the properties of the mechanical constituents (eg. mineral, collagen, etc.)
The fabric tensor [A] tells us
The distribution of the material (aka structure)
Plexiform bone is
A type of cortical bone; woven bone formed more rapidly than lamellar bone tissue; not found in humans
