Main findings
In this nationwide observational register study a bimodal age distribution of femur fractures was found only in boys. Falls and traffic accidents were the most common mechanisms of injury. Most fractures were treated non-surgically. The risk for surgery increased with age and was highest in shaft fractures compared to proximal and distal fractures.
Age, sex and fracture type
The bimodal age distribution seen in boys in this study is consistent with earlier findings [4, 5, 14]. The first peak occurs when children start to walk [4] while the second occurs during more high energy activities (e.g., motocross and rough play). These high energy activities take place more frequently in boy than in girls [15].
Our hypothesis that femur fractures are more common in boys than in girls was confirmed. The overall boy:girl ratio (1.8:1) in our study is lower compared to other studies (2.3:1 [4] and 2.6:1 [5]). One possible explanation for this discrepancy is that the studies use different age intervals. A wider age range will affect the boy:girl ratio in that adolescent boys are more often injured than adolescent girls [4, 5]. In addition, because we included pathological, stress and spontaneous fractures, comparisons are difficult to make with studies that include only traumatic injuries. However, a recent study [16] found the gap in physical activity between boys and girls to decrease, which explains the lower boy:girl ratio in femur fractures in our study.
In line with Loder et al. ‘s results, shaft fractures were the most common fracture type and thus confirmed our hypothesis [6]. We found that the proportion of shaft fractures was highest in the younger age group. In adults approximately 90% of femur fractures occur in the proximal femur [17]. Potential factors that may explain the difference in femur fracture patterns in pediatric patients compared to adult femur fractures are osteoporosis and a different manner of falling, including an increased risk of falling due to medication or impaired balance [18].
Mechanism of injury
Falls in younger children and traffic accidents in adolescents are the two most common causes of femur fractures, an observation confirmed in our study and others [1, 4, 6]. In the youngest children (0–3 years) falls from > 1 m were more common than falls from < 1 m. One explanation can be that these children not only fall when climbing play equipment and furniture but also fall from baby changing tables or converted dressers. In contrast, older children mostly fall because of slipping or physical activity. With the child’s increasing age, the most common injury mechanism shifted from falls to traffic accidents, a finding in accord with earlier results [1, 4, 6]. In our study traffic accidents accounted for 18% of femur fractures, a percentage comparable to that reported previously [4].
Non-accidental trauma was registered in 7% of the femur fractures in children < 3 years, a percentage at variance with earlier reports [4, 6]. Loder et al. reported that 15% of femur fractures in children under the age of 2 years were due to abuse [6], whereas Heideken et al. found that abuse accounted for only 4.2% of the femur shaft fractures in children aged < 1 year [4]. Our low numbers may be because fracture registration in the SFR is conducted at the time of treatment when the exact injury mechanism is not yet clear, or the investigation of the circumstances surrounding the injury is not completed. It is difficult to compare our results to those of other studies because some studies only included shaft fractures or a different age interval. The predominance of males in the stress/pathological/spontaneous fracture group is not clear. The finding can be explained by the presence of simple or aneurysmatic bone cysts dominant in males and often located in the femur, causing pathological fracture [19, 20].
Seasonal variation
Seasonal variations have been reported for femur fractures. For instance, Loder et al. noted an incidence peak in the summer; in contrast, Heideken et al. described a bimodal seasonal distribution, with one peak in winter/spring and another in summer [4, 6]. The differences in seasonal variation likely depend on where the study population lives. Countries (such as Sweden) with outdoor activities during winter months have shown a bimodal seasonal distribution of femur fractures [4]. In our study there were no clear peaks in the number of femur fractures during the calendar year, although a tendency for a bimodal seasonal distribution was observed. However, comparing the different counties in Sweden, a clear peak in femur fractures in Sweden’s mountain areas was noted in February and March due to skiing accidents. Traffic accidents increased during the spring and summer months, which are not surprising given that motorcycles are commonly used during the year’s warmer months.
Treatment
In general, surgical treatment increased with age and shaft fractures had an eight-fold higher OR for being treated surgically than proximal and distal femur fractures.
Proximal fractures
We found a wider variety of treatment methods for proximal fractures than for shaft and distal fractures. One explanation for the difference in treatment is that proximal fracture types and severity of the fracture require different treatment methods. In addition, the surgeon’s preference plays a sizable role in the choice of treatment [21]. Broadman et al. suggest that stable and non-displaced transphyseal fractures can be treated with spica casting in children aged < 4 years [22]. All displaced fractures in children > 4 years need to be treated surgically (e.g., pins, screws or plate fixation) [21, 23].
Shaft fractures
As in previous studies, non-surgical treatment was the most common treatment in younger age groups and surgical treatment increased with age [11, 24]. The capacity to remodel malaligned fractures decreased as age increased, and fracture healing time increased with age. Therefore, non-surgical treatment is often less aggressive and well-tolerated in younger children [25]. However, non-surgical treatment for an adolescent would risk angular deformity, leg length discrepancy, or both. Such treatment would result in prolonged hospitalization and absence from school and thus is not optional in this age group [10, 11]. From the age of 4 years, the most common treatment method for femur shaft fractures was intramedullary nailing (external fixation and traction were only used sporadically). These results correspond to those of Heideken et al., who demonstrated that external fixation and traction decreased from 1987 to 2005, being replaced by intramedullary nailing [4].
Distal fractures
Little et al. propose that non-surgical treatment is an option if the fracture is stable and non-displaced [26]. Operative stabilizing internal fixation is needed to minimize the risk of angular deformity, leg length discrepancy, or both in displaced fractures [26]. We found that non-surgical procedures were most prevalent treatment practice in all age groups.
Strengths and limitations
One strength of this study is that many hospitals report to the SFR, a nationwide register covering over 80% of Sweden’s orthopedic units (2019) [27]. Because of the SFR’s detailed reporting, many variables could be analyzed and compared to previous studies. Moreover, our study provides an updated overview of femur fractures in children and adolescents in Sweden.
Our study has several limitations. First, we could not report the incidence of femur fractures because complete registration of all femur fractures in Sweden during the study period could not be guaranteed. Missing data constitute a second limitation. For instance, treatment was not specified in 44 fractures. Moreover, surgical treatment may have better completeness in registrations than non-surgical methods as it is performed by orthopedic surgeons who are required to register the fractures. By contrast, patients treated non-surgically were sometimes treated by general pediatric surgeons not familiar with the SFR. Finally, the lack of patient-related outcome measurements for children registered in the SFR makes it impossible to determine the long-term functional impact on the patients.