The incidence of distal radius fractures in a Swedish pediatric population - an observational cohort study of 90 970 individual fractures

Background 40–50 % of all boys and 30–40 % of girls suffer from at least one fracture during childhood. A quarter of these fractures affects the wrist, making it the worst affected part of the body. Children often sustain the injury during play or sport activities. There has been a lifestyle change among European children during the last decades, and there is reason to believe that fracture incidence is changing. Methods For the purpose of this observational cohort study registry data was retrieved from the Swedish National Patient Register for all pediatric patients registered with a distal radius fracture during the period 2005–2013. Incidence rates were calculated for each year using data from Statistic Sweden on population size by age and gender. Results 90 970 distal radius fractures were identified. The mean age at the time of fracture was 10 years. In ages 10–17 the proportion of male patients was significantly larger. Seasonal variations were detected with peak incidences in May and September. A decreasing total fracture incidence was observed during the study period. Conclusions The incidence of distal radius fractures in a population 0–17 years in Sweden was higher among male than in female patients. The incidence was lower in 2008–2013 as compared to 2005. Further studies are necessary to reveal if the incidence will continue to decrease.


Background
Fractures are common injuries among children. Nearly 40-50 % of all boys and 30-40 % of girls suffer from at least one fracture during childhood [1,2]. Wrist fractures represent 25 % of all fractures in children [2,3]. The fracture most commonly occurs when the child falls on an extended arm [2,4,5]. Falling while playing in a monkey bar or a trampoline are two frequently reported trauma mechanisms for younger children while the teenagers tend to sustain fractures during sports [6]. The incidence has been reported to peak during early stages of puberty [7][8][9] when the volumetric bone mineral density is relatively low [7].
The injury is often benign and most children will recover without any major sequelae [10]. A majority of cases are treated non-surgically with a bandage or a forearm cast and sometimes with a cast that immobilizes the elbow, depending on patient age and the character of the fracture [10]. In case of fracture patterns too displaced to be tolerated, closed reduction with or without surgical treatment with percutaneous pinning is recommended [11]. Treatment with open reduction and internal fixation is uncommon in the pediatric population [10].
There is reason to believe that there has been a lifestyle change among European children during the last decades, due to a continuous introduction of new technical devices to a broad population. There are reports describing a decrease in time that children and teenagers spend on physical activities [12]. How these lifestyle changes affect children's health in general, and more specifically distal radius fracture incidence is largely unknown. Publications presenting fracture incidence in pediatric populations have shown an increasing trend for many decades [3,13,14]. A study in a British setting reports data from 2007 to 2014 and showed no change in incidence of distal radius fractures during that period [15].
Most of the available data regarding radius fracture incidence in children describes what has happened over decades and are limited to small populations or reports from regional findings. Knowledge is sparse regarding the fracture incidence development in the new and rapidly developing millennium.
The aim of this nationwide registry study was to investigate the incidence of distal radius fractures in the pediatric population in Sweden during 2005-2013.

Methods
This is a descriptive observational cohort study analyzing Swedish nationwide registry data from 2005 to 2013. The Swedish National Patient Register (NPR) contains data from mandatory registrations of all inpatient care since 1987, and outpatient care since 2001, and is kept by the Swedish National Board of Health and Welfare under the Ministry of Health and Social Affairs [16]. Diagnoses are registered through the Swedish version of the International statistical classification of diseases and related health problems 10th revision (ICD-10-SE) code system. The coverage of the Swedish NPR is high and data has been reported to be valid since 2005 [17].
Data were retrieved for all registrations of distal radius fractures in pediatric patients during the period 2005 through 2013. We chose 2005 as the study start to avoid possible low coverage in the registry during its first years of activity. Data was ordered from the NPR in 2014 thus limiting the study period to the end of 2013. Patients were identified by the occurrence of the ICD-10-SE codes S52.5 fracture to the distal radius or S52.6 fracture to the distal part of radius and ulna. The study population were all individuals 0-17 years at the day of diagnosis.
A fracture event was defined as the first time the diagnosis S52.5 or S52.6 appeared in the register. If the diagnosis code S52.5 or S52.6 reappeared after a period of at least 18 months without any registrations of a distal radius or ulna fracture, it was considered a re-fracture, and counted as a fracture event. Simultaneous bilateral fracture or repetitive fracture within 18 months were counted as only one fracture. All individuals were sorted into four age groups: 0-6 years, 7-10 years, 11-14 years, 15-17 years.
Data on population size was collected from Statistics Sweden [18] including numbers of inhabitants in oneyear age groups broken down by sex as for November 1st every year 2005 through 2013.

Ethics
Ethical permission was retrieved from the Swedish Ethical Review Authority, reference number 2013/105 − 31/ 2, 2014/1041-32, 2017/611 − 32. No patients were asked for permission to participate and no personal identifications were retrieved. All data is used on population basis to minimize the intrusion of integrity.

Statistics
The statistical software used was IBM SPSS Statistics, version 23 and 25 for Windows. Continuous variables were presented as means. Proportions were presented as percentages and were compared with Chi 2− test. Annual incidence was calculated as the number of fracture events divided by the population at risk and presented as incidence per 10 000 person years. Incidences were calculated for the entire study population and separately for each age category. Fishers test were used to calculate confidence intervals (C.I) for incidence rates. A Poisson regression model adjusting for age group, gender and population at risk was performed, and results are presented as crude and adjusted measures, with a 95 % C.I and according p-value.

Results
A total number of 90,970 distal radius fractures in patients aged 0 to < 18 years in Sweden were registered during the study period. The mean age at the time for fracture was 10 years (males: 10.73, females 9.33) years and the median 11 (males: 11, females:10) years.
The proportion of male patients in the total population was 60.3 %. The distribution between genders was equal in age groups 0-10 years, but the proportion of male patients was higher in patients 11-17 years (p < 0.001).
The incidence rate over the whole time period was 52.9/10 000 person years. Male patients aged 11-14 had the highest incidence rate (113-133/10 000 person years). Females fifteen years or older had the lowest incidence rate followed by children 0-6 years ( Table 1). The Table 1 The incidence rates of a distal radius fracture in Sweden during 2005 -2013 according to registrations in the Swedish Patient Registry presented as incidence rate per 10 000 person years per year and age group. 95% Confidence intervals from Fisher's exact test      incidence rate differed between age groups and gender during all the studied years ( Fig. 1). A significant variation over the year was detected (p > 0.001) with peaks in May 68,7/10 000 person years (95 % C.I 69.6-72.4) and September 73,2/10 000 person years (95 % C.I 71.8-74.7) fracture/ 10 000 person years (Figs. 2 and 3). The lowest incidence was found during December at 32,1/10 000 person years (95 % C.I 31.2-33.1).
The incidence as investigated in a Poisson regression model was lower each year 2008-2013 as compared to 2005 (p < 0.001) ( Table 2).

Discussion
This observational cohort study analyzing Swedish nationwide registry data describes the gender and age distribution as well as incidence rates of distal radius fractures during the period 2005-2013.
Our results confirm the findings of previous authors that distal radius fractures are more common in boys than in girls [15]. However, the incidence rates encountered in our data differed somewhat from that previously presented. In a study from a United Kingdom setting, the incidences were lower than in our study population. Exact comparisons are difficult since we have presented our study populations in different age groups. Differences in fracture incidence between countries may be explained by different cultures, with different playing habits, preventive measures and upbringing conditions [2]. Biological differences may also be present, as is the case in an elderly population where the Scandinavian population is known to be more prone to osteoporotic fractures [19], and hence subject to a high incidence of distal radius fractures. To the best of our knowledge, there is no such differences in predisposing biological factors in the growing skeleton.  In a Dutch study, the incidence rates in the corresponding age groups were approximately similar to our findings [13]. The incidence of distal radius fractures was shown to increase from 1997 to 2007. In contrast, our data suggest a decrease in incidence rates over our study period. We speculate that an extended study period of the Dutch material may reveal a similar slow-down or decrease in fracture incidence that we found. Another speculation may be that an extension of our study period might reveal that our findings of a lowered incidence was a temporary dip in an increasing overall tendency. Future studies are needed to confirm these suggestions.
Jerrhag et al. also present data of an increasing incidence 1999-2010 in a southern Swedish region. They have presented their results as mean annual change, thus not making it possible to discern a possible change in increase at the end of their study period [20].
In nationwide study from South Korea 2005-2009, Park et al. found a higher incidence rate than ours of 80/ 10 000 person years. In agreement with our study  findings, they report a decreasing trend in the late part of the study period [21]. In Germany Körner et al. studied the change in pediatric upper extremity fractures 2002-2017 and reported only a slight change in incidence rate during the study period [22].
There is data that supports that physical and mental wellbeing in children is associated with physical activity [12,23]. The association between physical activity and occurrence of fractures however is debated: In a study from the United Kingdom, Clark et al. (2008) suggested a positive association between a high level of physical activity and fracture risk in children [24]. In a Swedish population there was no increase in fracture risk in a long-term moderate exercise intervention program among schoolchildren [25]. The influence of physical exercise on fracture risk may act as a protective factor, if one believes that physical activity strengthens the bone structure and improves balance and coordination. It may also counteract childhood obesity and overweight that have been described to be associated with an increased risk of forearm fractures [26,27]. However, there is reason to believe that exposure to bicycling, tree climbing, monkey bars and trampolines would produce more fractures than computer games or similar digital entertainment. We therefore speculate that the decrease in incidence that we discern in our material may represent a change in injury patterns secondary to life-style changes in children. What long term effect this may have on children's health and future risk for pathology is yet to be investigated. Some limitations to this study are admitted. First and foremost, this is a registry study on a population level meaning that details at the individual level are not available. The results rely on the ICD-10-SE code of diagnosis registrations and no details on fracture type, fracture pattern or coinciding observations can be obtained or analyzed. The registry design, on the other hand, offers a nationwide and large study population during a long time providing a great amount of fracture data. The age groups were constructed to separate different populations with different activity patterns. The cut off of different age groups could have been set differently. We believe that all registries may have problems with a low coverage during the first years of registrations which explain our study period started in 2005 even if data was available in the registry from 2001. Another selection of study period could have been more appropriate.

Conclusions
The incidence of distal radius fractures in the Swedish population 0-17 years of age was lower in 2008-2013 as compared to 2005. Further studies are necessary to reveal if the incidence will continue to decrease. The incidence of distal radius fractures was higher among male than in female patients. There are seasonal variations in distal radius incidences with different patterns in different age groups.