What are the types of bone
What is the function of bone?
- Protect organs
- Support body
- Provide attachment
- Produce cells
- Store calcium
Draw a diagram of a long bone
What is an osteon and what is its structure?
Fundamental unit of compact bone
- Lamellae: Concentric ring of bone tissue
- Cement lines: Outer rings of bone tissue
- Volkmann canal: Contain transverse blood vessels connecting haversion canals
- Haversion canal: Blood vessels
- Lacunae: Holes for osteocytes
- Canaliculi:Osteocyte communication means
What are the two components of long bone?
- Trabecular(spongy) bone
Where do you find trabecular bone?
In epiphysis or metaphysis of long bone
Explain the heirarchical structure of bone and draw the diagram
Each bone has secondary osteons ->fibre arrays -> collagen fibrils -> mineralised collagen molecues
- Collagen fibrils and collagen fibres have enzymatic and non enzymatic cross links as well as hydroxyapatate
What are the components of bone?
Organic: Collagen for tensile strength and flexibility
- Hydroxyapatate for stiffness and compressive strength.
What are the three types of cells in bone and what are their functions?
- Lay down bone
- Make collagen fibrils and proteoglycans.
- Deposit apatite.
- Can become osteocytes
- Osteocytes: Perform mechanosensory and maintenance functions
- Sit in bone matrix and communicate with each other via canaliculi
- Long lived
- Osteoclasts: Secrete H+
- Secrete collagenase and proteinases to clear proteins
- THey are multinucleated and larger than osteoblasts
What are basic multicellular units? (BMUs)
Bone lining cells (Type of Stem cells) lining the endosteum
How does Bone turnover process work?
- Originiation:Mechanical stimulus starts process.
- Bone lining cells recruit osteoclasts
- Osteoclasts resorb bone, creating resorption pit
- Osteoclasts die
- Osteoblasts fill the pit and secrete osteoids
- Matrix is mineralised and matures
Explain timeline of bone turnover
- 3days: Activation
- 30 days: Resorption
- 90 days: Formation
- 6months: Mineralisation
- Maturation afterwards
What is Wolff's law?
Bone will adapt to any stimulus placed on it
What are the factors that affect the biomechanical properties of bone?
- Load rate: As load rate increases, so does young's modulus. Bone adapts to strain rates.
- But this makes it more brittle
- Orientation: Stronger in compression and stronger longitudinally due to anisotropic nature
- Creep: Has visoplastic properties- dependent on time history of strain.
- Strain changes under constant load.
- Age: Bone is less stiff, less strong, more brittle
Why does bone get weaker with age?
- Loss of bone quality
- Increased enzymatic cross linking between collagen fibrils
- Collagen fibrils can no longer slide over each other as easily to absorb impact
- This suppresses plascticity
Draw the graph to show how bones adapt to mechanical stimulus
- Higher daily stimulation leads to bone formation
- Lower daily stimulus leads to bone resorption
How does one measure bone mineral content?
DEXA (dual x ray absoptionmetry)
In what way will bone adapt to loads placed on it?
- Bone density: Spacing thickness, number
What the the types of bone fracture?
- Traumatic or non-traumatic
- Simple: Transverse, spiral, oblique.
To describe location: Proximal middle, distal.
What are the ways bone can detect mechanical stimulus
- Strain: Cells attached to stiff matrix which strains stretch receptors on cells
- Fluid flow: Canalicular channels have fluid.
- Osteoctes repond to fluid flow
- Microdamage? Strain energy density? Stress?
What approaches are there to bone fracture fixation
Stabilise: With nails screws, plates wires
Orthopaeidc hardware: Internal and external fixation methods
What internal fixation methods are there for fracture fixation
Compression plate, tendion banding, wires
What is the mechanism for fracture healing in 5 steps?
- Haematoma forms (blood clot)
- Granualation tissue forms (loose connective tissue)
- Cartilage formation
- Bone formation
WHat is osteoporosis defined as and why does it happen?
Bone density less than 2.5 standard deviations below the peak bone mass
- It happens due to too much resorption and too little formation
What are the risk factors of osteoporosis?
Gender: For women, estrogen normally regulates osteoclast apoptosis. Menopause causes decrease in estrogren. For men its decrease in testosterone
Other factors: Genetic, age, malnutrition, physical inactivity