Time Trends in Bone Mass and Fracture Incidence in Children

Abstract: Background: It is currently estimated that one third of all children will sustain fractures. However, there may also be time trends in pediatric fracture incidence. When predicting future fracture incidence, it is further important to evaluate bone mass, as low bone mass is a strong predictor of fractures. Such evaluation would help the society to allocate health care resources adequately. Aims: The aims of this thesis were to in children (i) update fracture epidemiology/etiology, (ii) identify possible time trends in fracture incidence, and (iii) identify possible differences in bone mass over time. Methods: In the epidemiological studies we included all types of fractures (Paper I), and the two most common type of fractures, distal forearm fractures (Paper II), and hand fractures (Paper III), that Malmö children aged 0–15 years had sustained in 2014–2016. Fractures were identified through the Skåne University Hospital (SUS) diagnosis registry, the radiological archive and medical charts. We compared these data with published data from 14 evaluated years during the period 1950–2006. Time trends were evaluated using joinpoint regression analysis and differences between two specific periods with incident rate ratios (IRRs) with 95% confidence intervals (95% CIs). We also measured distal forearm bone mineral density (BMD; g/cm2) by single photon absorptiometry (SPA) in 442 children aged 7–15 during the years 2017–2018 and compared these data with BMD in 116 children aged 7–15 measured in 1979–1981 (Paper IV). We present BMD versus age in the two cohorts as scatter plots with fitted linear regression slopes with 95% CI. Predicted BMD at age 16 was estimated with help of the slopes, with the difference between the two cohorts presented as proportional difference (%) and difference in standard deviation (SD). Results: The pediatric fracture incidence in 2014–2016 was 1,786/105 person-years, for distal forearm fractures 546/105 person-years, and for hand fractures 339/105 person-years. The pediatric age-adjusted fracture incidence increased from 1950 to 1979 and was thereafter stable, the age-adjusted distal forearm fracture incidence increased from 1950 to 2016, while the age-adjusted hand fracture incidence increased from 1950 to 1979 and decreased after that. The only difference in age-adjusted incidences, when comparing the period 2014–2016 with the most recent evaluated period 2005–2006, was a higher incidence in girls for all types of fractures in 2014–2016. Sports and playing injuries were common fracture-related activities. Children measured in 2017–2018 had an inferior BMD versus age slope than children measured in 1979–1981 (–5.6 mg/cm2/year, 95% CI: –9.6 to –1.5). The predicted BMD in 16-year-old boys in 2017–2018 was about 10% (–0.9 SD) lower than the predicted BMD value in 16-year-old boys 1979–1981. The corresponding value for 16-year-old girls in 2017–2018 was about 11% lower (–1.1 SD) than the predicted BMD value in 16-year-old girls 1979–1981. Conclusions: Pediatric age-adjusted fracture incidences have been stable in recent decades, while some fractures, such as distal forearm fractures, have increased, and others, such as hand fractures, have decreased. Children seem nowadays to develop lower BMD than four decades ago, changes that may indicate the risk of a future increase in the prevalence of osteoporosis and incidence of fractures.