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43 Cards in this Set
- Front
- Back
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What is the function of a skeleton? |
- Protect internal organs - Provide kinematic levers for muscles and attachment points - Store minerals (especially Ca) |
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What are the feature of bones? |
- dynamic and highly metabolically active - highly vascular and have high ability for self repair - able to change properties and architecture in response to mechanical stimuli |
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What is bone? |
- connective tissue consisting of cells interspersed in an organic ECM In ECM: - inorganic compounds (minerals) provide strength - organic compounds provide flexibility |
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What are the types of bone cells |
Osteoblasts, Osteocytes, Osteoclasts and bone lining cells |
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Where and what are Osteoblasts |
- cells on bone surface - promote bone growth by secreting proteins to anchor minerals on matrix |
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Where and what are Osteocytes? |
- trapped in matrix - terminally differentiated osteoblastic lineage cells |
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What are bone lining cells? |
Inactive (quiescent) osteoblasts |
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What are Osteoclasts |
- responsible for bone resorption and remodelling - multinucleated |
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What is the composition of bone? |
60-70% minerals (HA mainly) by dry weight 25% of total weight is water Type 1 collagen which minerals attach to in orderly manner |
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What is the macro composition of bone? |
Cortical - relative density of 0.7-0.95 - outer shell Trabecular - rods and plates - relative density of 0.05-0.7 - gaps filled with marrow Standard unit = 1.8 g/cm^2 |
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Explain the types of bone growth |
Primary: - Endochondral Ossification (endochondral = starts in cartilage, ossification = bone growth) Secondary: - constant process throughout life - bone resorption by osteoclasts and deposition by osteoblasts |
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What are the 3 types of primary bone? |
- woven fibered bone - primary osteons - circumferential lamellar bone |
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What is endochondral ossification? |
Bone growth by replacing cartilage with bone |
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Define Endosteal and periosteal |
The Inside surface (medullary cavity) and outside surface of bone respectively. |
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Define interstitial |
Occupying a small, intervening space |
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Describe cortical bone structure at birth |
- Largely consists of woven fibered bone - Random arrangement of collagen bundles produce irregular vascular spaces lined with osteoblasts |
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Describe the development of primary cortical bone |
- Osteoblasts produce many lamellae in cavaties, reducing vascular space, produce primary osteons - Also increases diameter of bones as more lamellar bone deposited circumferentially periosteally |
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Describe the development on secondary cortical bone |
- Process initiated by osteoclastic resporption of bone producing longitudinal tubular cavaties - Osteoblasts desposit bone forming successive lamellae, reducing cavity til only space for single vascular canal, formuing secondary osteons - interstitial bone in areas around secondary osteons, made of existing tissue |
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What is the structure of normal adult cortical bone? |
Many secondary osteons within circumferential lamellar bone both periosteally and endosteally |
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When might woven-fibered bone be present in adults? |
When rapid growth occurs e.g. fracture healing |
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Describe lamellar bone |
-Sheets ot tissue (7um) with radial collagen orientation
- Layers separated by cement layers (0.1um) |
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What is Wolff's law?
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The architecture and density of trabecular bone are related to the stresses arising due to daily living. |
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What happens to trabecular bone if loads are equal in all directions? |
Forms equiaxed cells |
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What happens to the structure of trabecular bone as the loads on it increase? |
-At low loads, many rods and low bone density - As load increases, cell wall thickens and spreads resembling perforated plate, |
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What is Osteoporosis?
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- Reduced bone density - Change in bone microarchitecture making it more vulnerable to fracture - Generally these changes take place in trabecular bone |
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What are the common types/causes of osteoporosis? |
- After 30 y/o bone density gradually decreases - After menopause, women's bone density decreases faster due to change in hormones (post menopausal osteoporosis) - When bones aren't loaded, their structure changes (disuse osteoporosis) |
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What are the classifications for bone loss according to the WHO? |
Compared to the average 25 y/o female: - more than 2.5D lower = osteoporotic - less than 2.5D lower = osteopenic |
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Where are the 3 most common places for fracture to occur due to osteoporosis? |
Hip, wrist, spine |
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What are the two phases in the bi-phasic representation of bone? |
- Minerals - Collagen |
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Compare the mechanical properties of cancellous and cortical bone? |
- Cortical bone is stiffer - Cancellous bone can absorb much more energy due to its porous structure - Cancellous bone can undergo 50% strain before YIELD whereas cortical only undergoes 1.5-2% before YIELD AND FRACTURE - Cortical bone is not completely linear elastic, it undergoes some yielding |
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Describe the two main factors affecting the mechanical properties of bone |
- Age - Younger bone is more ductile - Rate of Loading - Bones are VISCOELASTIC, they are stiffer at higher rates of loading |
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Describe the mechanisms for bone yielding in tension and compression |
Tension - osteon debonding at the cement line Compression - Cracking of the osteon |
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Bone is anisotropic, describe which directions the bone is most and least stiff and strong |
Greatest strength and stiffness in direction of most common loading in-vivo loading direction Weakest in transverse direction |
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Explain Bone Fracture Causes: Tension |
- Most frequently occurs in bone with large proportion of cancellous bone - Common cause is large loading from achilles tendon on ankle |
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Explain Bone Fracture Causes: Compression |
- Commonly occurs in vertabrae - Common cause osteoporotic compression |
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Explain Bone Fracture Causes: Shear |
- Commonly occurs in cancellous bone - Common cause - falling from a height |
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Explain Bone Fracture Causes: Bending |
- Commonly occurs in long bones (3 point bending) - Common cause - boot top fracture e.g. ski falls |
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Explain Bone Fracture Causes: Torsion |
- Initial crack parallel to neutral axis due to shear - Second crack diagonal to NA in plane of max tensile stress - Forms a spiral fracture |
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Explain Bone Fracture Causes: Combined Loading |
- Most not caused by single loading type- Creates complex stress pattern
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What is the difference in fracture patterns for high and low rate loading? |
Low rate - energy can be dissipated by single crack High rate - often results in bone shattering (causing soft tissue damage) |
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What effect does muscle contraction have on the stresses in bones?
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Reduces (or neutralises) tensile stresses |
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What loading factors effect likeliness of fatigue failure of bone (therefore stress fractures)? |
Magnitude of Loading Frequency of Loading Number of cycles |
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In which groups of people are stress fractures most common? |
Army recruits, athletes - where loading frequency too great to allow bone re-modelling. |
