The health and economic burden of osteoporotic fractures in Singapore and the potential impact of increasing treatment rates through more pharmacological options

Abstract

Purpose

This study aims to estimate the health and economic burden of osteoporosis in Singapore from 2017 to 2035, and to quantify the impact of increasing the treatment rate of osteoporosis.

Methods

Population forecast data of women and men aged 50 and above in Singapore from 2017 to 2035 was used along with prevalence rates of osteoporosis to project the osteoporosis population over time. The population projections by sex and age group were used along with osteoporotic fracture incidence rates by fracture type (hip, vertebral, other), and average direct and indirect costs per case to forecast the number of fractures, the total direct health care costs, and the total indirect costs due to fractures in Singapore. Data on treatment rates and effects were used to model the health and economic impact of increasing treatment rate of osteoporosis, using different hypothetical levels.

Results

Between 2017 and 2035, the incidence of osteoporotic fractures is projected to increase from 15,267 to 24,104 (a 57.9% increase) F 10,717 to 17,225 (a 60.7% increase) and M 4550 to 6878 (a 51.2% increase). The total economic burden (including direct costs and indirect costs to society) associated with these fractures is estimated at S$183.5 million in 2017 and is forecasted to grow to S$289.6 million by 2035. However, increasing the treatment rate for osteoporosis could avert up to 29,096 fractures over the forecast period (2017–2035), generating cumulative total cost savings of up to S$330.6 million.

Conclusion

Efforts to improve the detection, diagnosis, and treatment of osteoporosis are necessary to reduce the growing clinical, economic, and societal burden of fractures in Singapore.

Appendices

Technical appendix

Table 4 Population projections for adults 50 years old and over, Singapore, 2017–2035

Table 5 Base risk estimates by age and sex, Singapore, 2017

Table 6 Forecasted number of fractures by type, gender, age, and year

Example of how fracture rates were estimated for e.g. females aged 50–59 years

The base risks of fractures by gender and age group are calculated using the following formulae, given information on incidence rate, relative risk of fracture of osteoporotic patients vs. patients without osteoporosis, and the prevalence rate of osteoporosis.

$$ {\mathrm{Incidence}\ \mathrm{rate}}_{\mathrm{female},50-59,\mathrm{Hip}\ \mathrm{FX},\mathrm{basecase}}={\mathrm{Baserisk}}_{\mathrm{female},50-59,\mathrm{Hip}\ \mathrm{FX}}\times \left(\ {\mathrm{RR}}_{\mathrm{Osteo}}\times {\mathrm{Prev}\ \mathrm{rate}}_{\mathrm{Osteo}}+\left(\ 1-{\mathrm{Prev}\ \mathrm{rate}}_{\mathrm{Osteo}}\right)\right) $$

$$ {\mathrm{Incidence}\ \mathrm{rate}}_{\mathrm{female},50-59,\mathrm{Hip}\ \mathrm{FX},\mathrm{basecase}}=0.2530\% $$

i.e., the incidence rate of hip fracture for female patients is 253 cases per 100,000 persons. Given the population of females aged 50–59 is 456,978, the number of hip fracture cases for female aged 50–59 is 0.00253 × 456,978 = 1156.

Take an example of female patients in the age group of 50–59. The base risk of hip fracture is given by:

$$ {\mathrm{Baserisk}}_{\mathrm{Fractures}}={\mathrm{Incidence}\ \mathrm{rate}}_{\mathrm{Fractures}}/\left(\ {\mathrm{RR}}_{\mathrm{Osteo}}\times {\mathrm{Prev}\ \mathrm{rate}}_{\mathrm{Osteo}}+\left(\ 1-{\mathrm{Prev}\ \mathrm{rate}}_{\mathrm{Osteo}}\right)\right) $$

$$ {\mathrm{Baserisk}}_{\mathrm{female},50-59,\mathrm{Hip}\ \mathrm{FX}}=0.00253/\left(\ 1.9\times 15.2\%+\left(\ 1-15.2\%\right)\right) $$

$$ {\mathrm{Baserisk}}_{\mathrm{female},50-59,\mathrm{Hip}\ \mathrm{FX}}=0.22\% $$

In the treatment scenario, since we assume the increase in treatment is fully attributed to the use of denosumab, the relative risk of FX for the OP patients is the weighted average between RR_Osteoporosis and RR_Denosumab:

$$ {\mathrm{RR}}_{\mathrm{new}}=\Delta \mathrm{TR}\times {\mathrm{RR}}_{\mathrm{Denosumab}}+\left(1-\Delta \mathrm{TR}\right)\times {\mathrm{RR}}_{\mathrm{Osteoporosis}} $$

where ΔTR = 10%, 20%, 30%, or 47% uptake of denosumab.

RR_Denosumab is the relative risk of fracture of OP patients with intake of Denosumab, i.e., RR_Denosumab = RR_Osteoporosis × (1-relative risk reduction of denosumab by fracture type).

In the counterfactual exercise of ΔTR = 10% uptake of denosumab,

$$ {\mathrm{RR}}_{\mathrm{new}}=10\%\times 1.9\ \mathrm{x}\ \left(1\hbox{--} 40\%\right)+\left(1\hbox{--} 10\%\right)\times 1.9 $$

$$ {\mathrm{RR}}_{\mathrm{new}}=1.824 $$

The RR_new are then plugged into the incidence rate equation to imply the new incidence rate of fractures in order to predict the incidence of fracture by various scenarios.

The new incidence of hip fracture with a 10% uptake of denosumab is:

$$ {\mathrm{Incidence}\ \mathrm{rate}}_{\mathrm{female},50-59,\mathrm{hip},10\%}=0.22\%\times \left(\ 1.824\times 15.2\%+\left(\ 1-15.2\%\right)\right) $$

$$ {\mathrm{Incidence}\ \mathrm{rate}}_{\mathrm{female},50-59,\mathrm{hip},\kern0.5em 10\%\mathrm{uptake}}=0.2504\% $$

Given 10% uptake of denosumab, the incidence rate for female hip fracture patients, 50–59 years of age, is 250 cases per 100,000 persons. With the assumption of 10% uptake of denosumab, the number of cases in 2017 is 0.002504 × 456,978 = 1144.

Therefore, the number of hip fracture cases averted for female aged 50–59 is 1156–1144 = 12.