Osteoporosis is the most common bone disorder. It is a reduction in bone mass and alteration of bone structure, not just a reduction in bone density. The easiest way to measure the extent of the disease is with bone density scans.
The condition in itself is clinically silent
it massively increases the risk of fractures,
which increases the risk of mortality.
- Most common bone disorder
- Genetic factors are very important – in twins, concordance is 60-90%. Many genes have been implicated, and it is likely that numerous genes are involved.
- Osterogenesis imperfecta is a type of monogenic osteoporosis that has been well described, but is rare compared to multigenic and multifactorial causes. OI actually comprises of 4 subtypes, which are classified by the presence of a blue sclera. In some cases, this is apparent in childhood, but may resolve with age. In some cases, affected children are born with multiple fractures. There is also often joint hypermobility, aortic root dilation (causing aortic regurg) and hearing loss. These secondary features are related to defects in collagen.
- More common in women (4:1)
- More common in Caucasian population than in other races
- Affects 35% of the over 50’s in the UK
- Post menopausal bone loss is the most common cause – this is related to oestrogen deficiency
- Malabsroption (e.g. coeliac’s disease)
- Most commonly the result of vitamin D deficiency
- Multiple myeloma
- Family history
- Alcohol excess
- Late menarche
- Early menopause – including surgical menopause
- Lack of weight bearing exercise
- Including Cushing’s disease
- Extreme alcohol excess
- Low calcium and/or vitamin D intake
- Reduced height (vertebral fracture)
- Stooping posture – kyphosis, aka dowager’s hump – as a result of wedge shaped fractures of the vertebral bodies.
Essentially, there is loss of bone mass, despite normal mineralisation.
- As opposed to osteomalacia – which occurs when bone is not being properly mineralised, despite the normal production of bone matrix.
Caused by a loss of coupling between bone deposition and bone absorption mechanisms. This can result in excess osetoclast activity, decreased osteoblast activity, or both. The process of mineralisation of new bone matrix remains normal.
Osteoporosis affects both trabecular (long thick bones, e.g. femur) and cortical bone (high surface area, think bones, e.g. spine). When it affects trabecular bones, reabsoprtion of bone is the main mechanism.
Post menopausal osteoporosis
This is the most common type of osteoporosis. Bone mass naturally declines with age. Peak bone mass occurs several years after puberty, and then steadily declines. In women, this decline is increased during and after menopause. This, coupled with the fact that women have a lower peak bone mass than men, means post-menopausal women are at particularly high risk.
Reduced levels of oestrogen mean that normal osteoclast and osteoblast activity is no longer in conjunction, and osteoclast activity slightly exceeds osteoblast activity, so that over time, bone mass is reduced.