INTRODUCTION: Treatment of osteoporosis has made remarkable progress over the last two decade¹, however, only a few studies reported on the change in the prevalence of vertebral fractures (VFs) during that time. The purpose of this study was to compare the prevalence and pattern of VFs and the treatment rate for osteoporosis in three time points from 1997 to 2019 in a population-based cohort study.

METHODS: The inhabitants of a typical mountain village who participated in the surveys at three time points, 1997 (Group A), 2009 (Group B) and 2019 (Group C), were the subjects of this study. Age and gender-adjusted groups were defined as the Group A’, B’ and C’ (39 males and 85 females: mean age 73.6-74.0 y/o). Type (wedge, biconcave, crush) and extent (G1: mild; G2: moderate; G3: severe) of deformity of the prevalent fractures from T4 to L4 in lateral thoracic and lumbar spine radiographs were evaluated using a Genant’s semi-quantitative technique². Subjects whose Bone mineral density (BMD) was less than 70% young adult mean were defined as subjects with osteoporosis. The prevalence, vertebral level, and deformity type of VFs, and the treatment rate of osteoporosis were statistically evaluated using the chi-squared test with Bonferroni’s correction post hoc test.

RESULTS: 1. Prevalence of VFs: The prevalence of subjects who had VFs in the Group A’, B’ and C’ had deceased over the two decades (Fig.1). A significantly higher percentage than expected in the Group A’ (P<0.01) and a significantly lower percentage than expected in the Group C’ (P<0.01) were showed. The percentage of subjects with prevalent G2-3 VFs had also decreased over the two decades. The percentage of those in the Group A’ was significantly higher than expected (P<0.05). 2. Characteristics of VFs: In the Group A’, thoracic VFs was significantly more frequent than expected (P<0.05), while thoracolumbar VFs was significantly less frequent than expected (P<0.05). The percentage of biconcave type deformity was significantly higher than expected in the Group A’ (P<0.01) and significantly lower than expected in the Group B’ (P<0.05) (Fig. 2). On the other hand, the percentage of wedge type deformity was significantly lower than expected in the Group A’ (P<0.01). 3. BMD and osteoporosis treatment: BMD (young adult mean) had increased over time (Fig. 3a); and one-way ANOVA showed that BMD of the Group C’ was significantly higher than the Group A’ (P<0.05). The treatment rate of osteoporosis in the subjects with osteoporosis had improved over the two decades (Fig. 3b). The treatment rate was significantly lower than expected in the Group A’ (P<0.01) and significantly higher than expected in the Group C’ (P<0.05).

DISCUSSION: This study demonstrated, for the first time, that the prevalence of VFs had decreased over the two decades in a typical Japanese mountain village. These data suggest the possibility that the early diagnosis and use of therapeutic drugs for osteoporosis and resulting improvement of BMD would contribute to a continuous decrease in the prevalence of VFs, especially in biconcave type VFs.