Fracture incidence and association with bone mineral density in elderly men and women: the Rotterdam Study
Introduction
Osteoporosis is a condition characterized by low bone mineral density (BMD) and micro architectural deterioration of bone, resulting in a loss of bone strength and therefore increased fracture risk. Osteoporotic fractures, the clinical endpoint of osteoporosis, are associated with increased morbidity, mortality and high socio-economic costs [1], [2]. Due to increased life expectancy, the incidence of fractures is increasing over time, hereby increasing the population burden of fractures [2].
As early as 1842, Antley Cooper [3] noticed that the incidence of fractures increased with thinning of bone in the elderly. In the 20th century, several studies have shown that, independent of age, the likelihood of a fracture increases with decreasing BMD [4]. However, the majority of these studies focused on women only. Therefore, the relationship between BMD and fractures in men is largely unknown. Furthermore, due to limited power, most studies focus on the most common osteoporotic fractures such as hip fractures. Therefore, information on the occurrence as well as the relationship to BMD of less common osteoporotic fractures in men and women is scarce.
In clinical practice, the definition of osteoporosis is based on the WHO-based T-score of BMD, which expresses BMD as the number of standard deviations (SDs) below the average BMD in young adult men and women. In this definition, subjects with a T-score at or below −2.5 are considered to have osteoporosis. Similarly, osteopenia is defined as a T-score between −1.0 and −2.5, whereas a T-score above −1.0 is considered normal [5]. These cut-off values were originally intended to assess the prevalence of osteoporosis, and not, as is common practice nowadays, to be used as a treatment threshold. Currently, there is ongoing debate about the strengths and limitations of bone densiometry in clinical practice.
The aim of our study was to investigate the incidence of the common osteoporotic fractures as well as less common fractures in both men and women in the Rotterdam Study, a large population-based study of diseases in the elderly. Furthermore, the association between femoral neck BMD and these fractures is compared between men and women. And finally, the sensitivity of using a T-score at or below −2.5 to identify subjects who will eventually sustain a fracture is studied.
Section snippets
Study population
The Rotterdam Study is a prospective population-based cohort study of men and women aged 55 and over. The objective is to investigate the incidence of and risk factors for chronic disabling diseases. Both the rationale and the study design have been described previously [6]. The focus of the Rotterdam Study is on neurological, cardiovascular, ophthalmologic and locomotor diseases. The Medical Ethics Committee of the Erasmus Medical Centre has approved the Rotterdam Study. All 10,275 inhabitants
Results
Follow-up was completed for 7806 individuals (3075 men) after a mean follow-up time of 6.8 years (SD 2.3 years, range 1 day to 10.5 years). BMD measurements were available for 5794 individuals (2437 men). Women were on average 2.4 years older and had 0.07 g/cm2 lower mean femoral neck BMD.
Discussion
In this population-based prospective cohort study of fractures, the most frequent non-vertebral fractures in elderly men and women are those of the wrist, upper humerus and hip. The risk of these fractures particularly increases with decreasing femoral neck BMD, an association that is similar in men and women. However, in absolute numbers, most non-vertebral fractures occur in individuals without osteoporosis (T-score above −2.5), suggesting that although low BMD is a strong risk factor for
Acknowledgements
This study is supported by the Netherlands Organization of Scientific Research (NWO) Research Institute for Diseases in the Elderly (grant 014-90-001). The authors are very grateful to the participants of the Rotterdam Study and to the DXA and radiograph technicians, L. Buist and H.W.M. Mathot. Furthermore, we acknowledge all the participating general practitioners and the many field workers in the research center in Ommoord, Rotterdam, The Netherlands.
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Both authors contributed equally to this work.