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[Aging as a cause of hip fractures; a theoretic mathematical model]
B Reichgelt1, L Bonneux, J M van den Bosch
1Instituut Maatschappelijke Gezondheidszorg, Erasmus Universiteit, Rotterdam.
Objective:
To estimate the numbers of hip fractures among Dutch women caused by senescence in contrast to decreasing postmenopausal bone loss.
Design:
A Markov chain model in a multi-state life table.
Setting:
Department of Public Health, Erasmus University of Rotterdam, the Netherlands.
Method:
Cross-sectional data of prevalences of femoral neck bone mineral density, measured in an epidemiological survey (1993), were related to numbers of hospital admissions for hip fractures among women aged 55 and older, using a (published) relative risk for hip fracture of 2.6 (95% confidence limits: 1.9-3.6) per decrease by I SD of bone mineral density. We varied the prevalences of bone mineral density in the multi state life table and looked at changes in the expected number of fractures.
Results:
If bone loss were to cease after the age of 55, this would decrease the number of fractures by 39.4% (30.4%-45.2% in sensitivity analysis). If bone loss were delayed by 7.5 years, the number of hip fractures would decrease by 14.8% (10.0%-19.9% after 5 to 10 years' delay). If compliance decreases by age (3% per year), then the number of hip fractures would decrease by 5.6% (3.4%-11.0% after 1%-5% decrease of compliance per year).
Conclusion:
Bone loss is only one of the many age related causes of hip fractures. Population based interventions targeting only bone mineral density, while ignoring comorbidity, have only a limited potential for preventing hip fractures.