Cumulative incidence and changes in the prevalence of vertebral fractures in a rural Japanese community: a 10-year follow-up of the Miyama cohort

INTRODUCTION: The objective of this study was to clarify secular changes in the prevalence and cumulative incidence of vertebral fractures (VFx) among the general inhabitants of Miyama, a rural Japanese community. METHODS: A cohort of 1,543 inhabitants aged 40–79 years was established using resident registration in 1989. Of these, 400 participants were selected and divided into four age strata, each containing 50 men and 50 women. Participants completed a self-administered questionnaire and anthropometric measurements were taken. In 1990, baseline radiographic examinations of the thoracolumbar spine in anteroposterior and lateral views were performed. Radiographic examinations of the same sites were performed on the same participants in 2000. All VFx were diagnosed by the same experienced orthopedic surgeon. Evaluation of radiographic surveys after 10 years was completed for 287 of the 400 participants (132 men, 155 women; 71.8%). RESULTS: The prevalences of VFx at follow-up in 2000 for subjects in their 50s, 60s, 70s, and 80s were 2.9%, 10.3%, 13.2%, and 25.0% for men, and 2.1%, 9.1%, 20.5%, and 54.2% for women, respectively. Prevalence in the present study was compared with that collected in 1990, showing improvements over time for men and women in their 50s, 60s, and 70s. Future problems with osteoporotic fractures in Japan might, thus, be less severe than previously predicted. Cumulative incidence over 10 years was detected by the number of incident cases divided by the number of all participants in the initial study. Incident cases were defined by two criteria. First, cases with prevalent VFx were excluded from both the numerators and the denominators. In this analysis, the cumulative incidence of the cases with first VFx was detected. Secondly, the cumulative incidence including the subjects who had suffered from the prevalent fractures and with an increased number of VFx in the following 10 years were calculated. This analysis clarified the cumulative incidence of cases with and without previous VFx. Incidence over 10 years of subjects in their 40s, 50s, 60s, and 70s with first VFx were 2.2%, 4.9%, 5.1%, and 10.8% for men, and 2.1%, 4.5%, 14.0%, and 22.2% for women, respectively. By contrast, if new cases were defined as including subjects who had suffered from previous fractures, but displayed an increased number of VFx, cumulative incidences for subjects in their 40s, 50s, 60s, and 70s were 2.1%, 8.3%, 10.0%, and 12.2% for men, and 2.1%, 6.1%, 18.0%, and 22.4% for women, respectively.