Background to osteoporosis

Osteoporosis is characterised by both low bone mineral density (BMD) and micro-architectural deterioration of bone tissue, leading to decreased bone strength, increased bone fragility and a consequent increase in fracture risk. Osteoporotic fractures usually result from falls from a standing height or less in individuals with decreased bone strength. BMD can be reliably measured by scanning of the axial skeleton by dual energy X-ray absorptiometry (DXA).

BMD is usually reported as a T-score, the number of standard deviations (SDs) of the BMD measurement above or below that of young healthy adults of the same sex. The World Health Organization (WHO) has defined osteoporosis and osteopenia on the basis of T-score (Table 1).1 While Australia’s Pharmaceutical Benefits Scheme (PBS) uses the WHO T-score range for osteoporosis to determine eligibility for subsidy on osteoporosis medications, it is important to note that BMD is only one of several factors that contribute to an individual’s risk of fracture. Approximately 50% of first or subsequent minimal trauma fractures occur in people who have T-scores in the normal or osteopenic range.2,3

Table 1.WHO definitions of osteoporosis and osteopenia

Table 1.

WHO definitions of osteoporosis and osteopenia1

Osteoporosis is known as a silent disease because the deterioration of skeletal tissue proceeds with no outward symptoms until a symptomatic fracture occurs, and thus the condition is under recognised and affected individuals are under treated.4,5

Vertebral fractures may cause no recognisable symptoms for the patient or may present with an acute self-limiting episode of back pain. However, subclinical fractures are important predictors of future fracture risk.

More commonly, vertebral fractures are associated with gradual height loss with increasing thoracic kyphosis and back pain. Non-vertebral or peripheral fractures usually present with more obvious fracture symptoms following a fall, although stress fractures may present as acute regional musculoskeletal pain.

Based on the WHO definition of osteoporosis and osteopenia, approximately 3% of men and 13% of women in Australia 50–69 years of age are osteoporotic, rising to 13% and 43% for men and women older than 70 years of age.6 Fifty-five per cent of men and 49% of women between 50 and 69 years of age are osteopenic, with similar prevalences in the over-70 years age group.6 It is estimated that by 2022 approximately 72% of women and 62% of men older than 50 years of age will have osteoporosis or osteopenia, according to WHO criteria.6,7

Approximately 70% of minimal trauma fractures occur in women, with incidence increasing with age in both sexes.6

The residual lifetime risk of minimal trauma fracture is approximately 44% for women older than 60 years of age.8 The residual lifetime fracture risk among men is lower, but still substantial and higher than for many other chronic conditions, being around 25% for those older than 60 years of age.8

Between the ages of 50 and 69, non-hip, non-vertebral fractures (humerus, ankle, lower limb, rib, forearm, pelvis, forearm [not wrist], patella, foot and hand) are the most common minimal trauma fracture types in both men and women.6 Wrist fractures are also common in women in this age group. The hip-fracture rate increases substantially with age, constituting only 4% of fragility fractures in women 50–69 years of age, but 26% of fractures in women older than 70 years of age.6 A similar trend with age is seen in men, although the overall incidence of hip fracture in men remains around one-third of that in women.6 The age-standardised hip-fracture incidence rate declined in Australia between 1997 and 2007, after a rise in the 1980s and stabilisation in the 1990s.9 However, the absolute number of hip fractures increased during this period.9 Any continued decline in incidence will be offset in the coming decades by the effects of an ageing population; the number of Australians older than 70 years of age is set to more than double from 2.2 million to almost five million by 2050.7

Vertebral fractures due to osteoporosis are associated with significant long-term disability due to pain and kyphosis. Vertebral fractures are usually defined on the basis of a 20% or more reduction in vertebral height on X-ray, and are often termed a ‘vertebral deformity’. The prevalence of radiologically identified vertebral deformities ranges from 5% in people aged 50–54 years to 50% in those over 80 years of age.10 In 2012, an estimated 25,502 vertebral fractures occurred in Australia.6 By 2022, incidence is expected to rise to over 35,000, an increase of 37%.6 The underdiagnosis of vertebral fractures is a major problem. Only around one-third of all radiographically observed vertebral deformities come to medical attention (ie are symptomatic with acute fracture-related pain).11 The worldwide Improving Measurements of Persistence on Actonel Treatment (IMPACT) study reported that in Australia, approximately 30% of radiographically visible vertebral fractures in women with osteoporosis are not detected.12

Osteoporosis is a systemic condition. Almost all types of fracture are increased in patients with low BMD, and irrespective of fracture site, adults who sustain a minimal trauma fracture (and possibly even a high trauma fracture) are at subsequently greater (2–4-fold) risk of sustaining another fracture at a different site.6,13 Vertebral deformity is particularly associated with significantly higher risk of subsequent vertebral and non-vertebral fracture.14

Morbidity related to fractures can arise from pain, reduced mobility, loss of function and associated loss of quality of life.15

Many patients lose the ability to live independently following a hip fracture. Long-term morbidity is associated with almost all types of symptomatic osteoporotic fractures – only subjects with wrist, humerus or ankle fractures return to their pre-fracture health-related quality of life 18 months after a fracture.15

Mortality in the first year after a major minimal trauma fracture in people older than 60 years of age is up to three times higher than in age-matched non-fracture populations for people with hip fracture and up to two times higher for other major fracture types.16–18 The mortality rate (per 100 person years) is higher in men than in women following any type of minimal trauma fracture; this effect is most pronounced in hip fracture.18 The risk of death is greatest in the first year after hip fracture: approximately 20% of women die within a year of fracturing a hip,18 with 10% dying during hospitalisation.19 Increased mortality during the immediate post-fracture period is associated with advanced age and male sex, and has been linked both to the presence of comorbid conditions such as congestive heart failure and liver disease,20 and to the fracture event itself.21 Acute events such as post-operative infections and complications are also important.

Although hip fracture has the highest mortality, followed by pelvic and vertebral fractures, a quarter of excess mortality due to minimal trauma fracture is attributable to non-hip, non-spine fractures, due to the high prevalence of these fractures.18 Excess mortality occurs mainly in the first five years after a minimal trauma fracture, but may continue up to 10 years following the fracture.22

Osteoporosis treatment has been shown in randomised controlled trials (RCTs) to significantly reduce mortality risk after hip fracture in elderly men and women,23,24 and cohort studies suggest this may also be the case for other fracture types.25 The mechanisms behind mortality reduction remain speculative. Bisphosphonates may regulate immune processes and/or ion channel activity, with consequent effects on risk of infection, as well as cardiovascular and cerebrovascular events. Potent suppression by bisphosphonates of bone turnover and bone loss is another potential mechanism; bone loss and high bone turnover are independent predictors of mortality.25

Pharmacological interventions prevent further bone loss and reduce fracture risk. Treatment decisions should be based on age, sex, medical history, severity of the condition and estimated absolute risk of fracture. Despite high-level evidence for efficacy, safety and cost-effectiveness, less than 30% of Australian women and 10% of Australian men with osteoporosis (even with minimal trauma fractures) report taking specific osteoporosis-targeted pharmaceuticals.26 Most current osteoporosis medications are anti-resorptive, and reduce the natural but excessive process of bone loss. Other agents increase the formation of new bone; these are most appropriate for more severe osteoporosis, especially if a patient is unresponsive to anti-resorptive therapy.

Modifiable risk factors are important in both the treatment and prevention of osteoporosis. A routine approach to addressing modifiable risk factors in general practice includes encouragement and support to increase weight-bearing exercise and strength training, maintain a healthy diet, ensure safe levels of sun exposure and avoid smoking and excessive alcohol intake. Exercise can assist in relieving pain as part of the post-fracture rehabilitation process. Only about 20% of Australians with osteoporosis report exercising most days and 6% do strength training.26 Specific osteoporosis self-management programs are conducted by various public hospital health-promotion units and community health centres. These usually focus on education and awareness about the disease process, prevention of fractures, pain management, rehabilitation techniques and falls prevention. However, particularly in rural and remote settings, it is likely that patient education will need to be coordinated and/ or undertaken by general practice with links to local allied health services.

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Related documents

  Osteoporosis-flowchart.pdf (PDF 0.98 MB)