Lecture 27; Metabolic Bone diseases Flashcards
What are the types of bone?
Spongy (trabecular)
Compact (osteon) (cortical bone)
What sort of tissue is bone?
- Connective Tissue
- Dynamic balance between reabsoprtion and deposition
What happens to bone with age?
Menopause / really old (60) age in men results in bone reabsoprtion > Deposition
Give a brief description of bone?
Made of collagen fibres that have become part of a calcified matrix.
When looking macroscopically at bone what can be seen?
Smooth = Bone covered in lining cells derived from osteobasts
Rough = Osteoclast activity / bone remodelling site
How do osteoclasts function?
Release HCl = removes mineral structures
Releases proteolytic enzymes = removes collagenous structures
What do osteoblasts do?
Deposit collagen (osteoid) this becomes mineralised
How often is the entire skeleton replaced?
~10 years
What happens in osteoporosis?
When bone reabsoprtion exceeds bone deposition
- Less bone
- Less robust plates
- If a trabeculae rod is punched through the middle then the remaining partial rods will waste away as they are not load bearing.
What is the actual definition of osteoporosis?
Thinning of bone and destruction of the micro architecture.
What have clinical trials shown regarding trying to manipulate osteoclast activity in osteporosis?
Huge clinical trial that pharmacologically switched off osteoclasts reduced the number of fractures compared to the placebo group
- but no increase in bone density
However the microarchitecture was preserved.
Therefore prevention is better overall than a cure and it is never too late to intervene.
What does age do to bone?
Reduces its density and porosity esp. in women.
Bone, trabeculae thin, eventually reduction in trabeculae numbers.
What does the thinning of bone of age lead to?
Vertebral compression fractures are common as the bone can no longer bear load
This can result in kaposis (curved back) as front of vertebrae break more than back
When looking at bone density across a population what is it important to note?
- Bone density is normally distributed and remains this way with age even though whole population at older age has lower bone density
- Young adults / most people are not osteoporotic
- 50 = hardly any changes
When looking at the bone density on a population scale what is seen at 50-90?
- Ongoing bone loss
- Females by 80, 50% will have bone densities in the osteoporotic range
- Doesnt guarantee fracture but increases risk.
Describe the fracture risk of women in the us;
- Colles fracture risk inc. @50-60 then plateaus
- Spine fracture risk inc. throughout life
- Hip osteoporotic fractures at 75+ rapidly increases in risk
Describe the fracture risk of men in the US
Hip + Spine 80+ fracture risk increases rapidly
What is a hip fracture associated with?
- loss of independence
- 20% mortality
How many women will have an osteoportic fracture by death?
50%
How do we access fracture risk?
Bone densitometry
Clinical Risk Factors
What are the clinical risk features for fractures?
Age
Weight (low weight
What is a major osteoporotic fracture?
Major osteoporotic fracture is hip fracture, clinically evident vertebral fracture, proximal humerus fracture and distal forearm fracture. This is about half of total fractures
Does being physically active prevent fractures?
Mixed evidence
Reality might be that fit people are better are preventing falls.
What do osteocytes monitor and how do they regulate osteoclasts and osteoblasts?
Osteocytes = Have processes to monitor degree of bone loading, then can regulate osteoclasts (RANKL - turns them on) and osteoblasts (Sclerosin-turns them off)
= ALL IN RELATION TO LOAD BEARING
