Definition and diagnosis of osteoporosis
Osteoporosis comes from "osteo", meaning bone, and the Greek word "por" (passage) – i.e. simply, it means porous bone.
Normal bone is composed of a mixture of calcium and other minerals such as magnesium and phosphate. It is also made up of collagen (protein), which forms the structural framework of bone.
Osteoporosis occurs when there is a loss of mineral from bone mainly in the form of calcium as well as architectural loss of normal bone structure. The loss of mineral content of the bone is referred to as a loss of bone mineral density in the bone.
Osteoporosis results in loss of bone strength, thus making bone more fragile and easily susceptible to fracture.
It is a process that affects all individuals and is a part of normal aging. All individuals if they live long enough will develop osteoporosis. Some individuals due to various illnesses or as part of hormone deficiency states will develop osteoporosis at an earlier stage in their life. After menopause women are at an increased risk of osteoporosis.
In itself, osteoporosis causes no symptoms. It is when fractures occur that the problems of osteoporosis arise.
Diagnosis of osteoporosis
In past years osteoporosis was diagnosed by plain x-ray which may have shown bone tissue to be less dense on x-ray or the presence of crush fractures.
Today the diagnosis of osteoporosis is guided by measurement of the amount of mineral in bone (mainly calcium) by a special x-ray technique called a Dual Energy X-ray Absorptiometry scan (DEXA scan) – see below. When osteoporosis is indicated by DEXA the diagnosis really relies on an increased risk of having a future fracture determined by a mathematical formula rather than a disease diagnosis.
This is important as over 50% of older women who in fact have an osteoporotic fracture seen on plain x-ray in fact have normal bone density on DEXA scan (Greenspan S et al, J Clin Densitom 2001; Davis SR et al Menopause 2010).
Therefore, screening older women (over 70 years of age) for osteoporosis requires a plain x-ray of the spine to identify fractures, ideally combined with a DEXA scan.
Osteopenia is diagnosed when there is reduced mineral content in bone, but not as low as to be considered osteoporosis.
Understanding your DEXA study result
If you are over 40 years old, your DEXA result will be reported as a T score.
When a DEXA study is performed, the bone mineral density is measured and compared to the bone mineral density of twenty year olds of the same sex. Twenty year-olds are used for comparison as they have the greatest peak bone mass.
Your T score is the number of "standard deviations" by which your bone density differs from that of a young adult.
If your T score is between +1.0 and -1.0 it is within the range of normal.
If your T Score is -1.0 to -2.5 you are said to have reduced bone density (osteopenia). Osteopaenia is not osteoporosis. It represents a stage when the bones have lost some bone mineral strength and are weaker, but not as weak as in osteoporosis.
If your T score is below - 2.5 this indicates the presence of osteoporosis.
Bone density of the hip measured by DEXA provides the most reliable risk prediction for future fracture.
DEXA bone mineral density values
|T Score at -1.0 and above||Normal bone mineral density|
|T Score between -1.0 and -2.5||Osteopenia|
|T Score at or below -2.5||Osteoporosis|
|T Score at or below -2.5 with one or more fragility fractures||Severe osteroporosis|
World Health Organisation Working Group Definition of Osteoporosis
How common is osteoporosis?
- After the age of 60 years, 1 in 2 Australian women and 1 in 3 Australian men will sustain an osteoporotic fracture.
- Of all osteoporotic fractures in Australia, 46% are vertebral fractures, 16% are hip fractures and 16% are wrist fractures.
- Hip fractures are particularly problematic as there is evidence to suggest that 50% of elderly patients sustaining a hip fracture need subsequent long-term nursing care.
- There also is an increased risk of mortality associated with hip fractures with some figures indicating that 15% of hip fractures in the elderly lead to death within 4 months of the fracture.
Causes of osteoporosis
During childhood and adolescence, the bones within the skeleton are actively growing. By one's early 20s, growth and development of bone is complete. This phase of bone development represents the attainment of "peak bone mass". It essentially is a time when bones are 'strongest'.
The peak bone mass that is achieved varies from one individual to the next and primarily reflects what has occurred during growth and development in childhood and adolescence. It is also influenced by genetic factors as well. Hence an individual who has had adequate intake of vitamin D, calcium, plenty of exercise and not been subjected to any sex hormone deficiencies (e.g. interruption to menstrual periods) during childhood and puberty will likely achieve a high peak bone mass as compared to the individual who has not had favourable circumstances for bone development during childhood and adolescence.
Normal ageing lead to a gradual loss of bone mineral density, usually over several decades, often starting from the late 30s.
The higher the peak bone mass that is achieved by the early 20s, then the greater the likelihood of withstanding the effects of normal age related bone loss. Individuals with a low peak bone mass, may not withstand the effects of age related bone loss as well as those who have achieved a high peak bone mass and hence may develop osteoporosis at a younger age.
Certain medical illnesses also effect bone and can lead to the development of osteoporosis, often independent of peak bone mass. People who have any of the following are eligible for a Medicare supported bone density study in Australia and should have a bone density study performed.
- Overactive thryroid
- Coeliac disease / other causes of malabsorption
- Chronic kidney disease
- Chronic liver disease
- Rheumatoid arthritis
- Ongoing treatment with glucocorticoid therapy (eg., Prednisolone)
- Loss of testicular function (men)
- Loss of ovarian function before natural menopause (women)
Disclaimer: The above information is a general guide and was accurate at the time of production of this page. This information is designed to complement, not replace, the advice of your health professional.