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Discussion
Our study has shown that long-bone fractures were independently associated with child age over 12 months, younger maternal age, increasing birth order and maternal alcohol misuse. Importantly, we have shown that these risk factors are apparent in a large, general population cohort identified through electronic primary care medical systems; demonstrating the usefulness of primary care data for the identification of families at higher injury risk.
Strengths and Limitations
The main strengths of our study are the large study size and that risk factors were prospectively recorded on the medical record before the fracture event. We matched cases and controls on general practice, accounting for differences in data recording between practices and over time. Data held in THIN are representative of the UK population in terms of age, sex and geographical coverage, and although there is yet to be a study assessing the ethnic breakdown of THIN, a study using a similar database found an ethnic breakdown similar to the 2011 Census. Our findings are therefore likely to be generalisable to the UK population.
Data in THIN are however not primarily collected for research purposes and so we were unable to assess injury mechanism (eg, falls from heights), location (eg, home) or intent (eg, maltreatment) as these data are poorly recorded in primary care, and in some cases injury intent may be clinically misdiagnosed. Fractures resulting from intentional harm predominantly occur in children less than 18 months, with the proportion of such fractures varying widely; estimated as 11–56% of fractures in children less than 12 months. By including some fractures resulting from intentional harm, we may have overestimated the effect of risk factors such as maternal alcohol misuse that have previously been associated with intentional injuries. The impact of this should however be relatively small as only 10% of fractures in this study occurred in those less than 12 months, and only a proportion of these are likely to have resulted from intentional injury.
The recorded prevalence of alcohol misuse was lower within our dataset than identified through other sources, and as we did not explore the effect of other drinking patterns (eg, binge drinking), the overall impact of maternal alcohol consumption may be greater than we have estimated. In addition, we have not adjusted for some potential risk factors, such as ethnicity, which was poorly recorded in primary care during the study time period, preterm birth, and rare medical conditions that can predispose children to fractures (eg, osteogenesis imperfecta). We were also unable to assess paternal risk factors for injury, as it is difficult to accurately identify fathers within primary care data.
We may not have identified some long-bone fracture cases if GPs did not receive correspondence about ED attendances or hospital admissions, a Read code was not entered in the medical record, or a code was used that did not specify the anatomical site of fracture. We however attempted to maximise our case ascertainment by using a broad definition of long-bone fractures. This is unlikely to have biased our findings, as even when using the most specific long-bone fracture definition in our sensitivity analysis, the findings were similar. Any under-ascertainment of long-bone fractures, unless associated with child, maternal or household risk factors, would be likely to underestimate observed associations in this study.
Comparison to Existing Literature
Our finding of a marked increase in the odds of fracture among children over 12 months is consistent with previous studies; and is likely to reflect developmental changes and the commencement of walking. Similar to previous injury studies, we found an increased odds of long-bone fracture with higher birth order. We did not however find an association with the number of children in the household, indicating that birth order, which gives information about the relationships between children, may be more important than the general number of children in the household. Mechanisms for this association could include reduced parental supervision due to more children being in the household, activities or games children are exposed to through having older siblings, and older children being responsible for supervising younger siblings.
Evidence on associations between socioeconomic status and childhood fractures is conflicting. Similar to two studies, we found no association between the odds of fracture and socioeconomic status. Comparatively, a cross-sectional study by Hippisley-Cox et al found that children from the most deprived areas were more likely to be both hospitalised and have an operation for a long-bone fracture than children from the most affluent areas. Our findings may differ, as we included all long-bone fractures and not just hospitalised cases, and we focused on first fracture events. Previous studies have demonstrated that children sustaining recurrent injuries are more likely to have social risk factors (eg, family violence), and so the lack of association in our study could be explained by our focus on first fracture events.
To our knowledge, few studies have assessed the impact of maternal alcohol misuse on childhood fractures; although there are studies of other injury types where an association has been found. Associations between maternal alcohol misuse and childhood injuries could relate to alcohol influencing supervisory practices, the presence of hazards or the uptake of injury prevention practices; although our interpretation is limited by not having data on mothers' alcohol consumption at the time of the fracture.
Implications for Practice and Research
Preventing childhood injuries requires multiagency action that includes a range of measures from education to environmental modification and legislation. Among preschool children, over two-thirds of injuries occur within the home environment, and so clinicians such as GPs, health visitors and paediatricians can, where appropriate, refer high risk families to home safety assessment and equipment schemes in accordance with NICE guidelines on preventing injuries. It is also important that parents are made aware of key developmental stages and the associated injury risks, so that they can anticipate potential hazards. Within primary care, brief alcohol interventions have been shown as effective, with growing evidence to support family focused interventions. While further research on associations between childhood fractures and maternal alcohol misuse would be beneficial, interventions to reduce maternal alcohol consumption could improve the health of the mother, alongside potentially reducing childhood injuries. At a population level, public health teams should prioritise interventions to communities where children are at the greatest risk of injury. From our study, households with younger mothers, multiple older siblings and where mothers misuse alcohol should be prioritised. Future research could assess how these risk factors change among children who sustain repeated long-bone fractures or fractures at other sites indicating severe injury (eg, skull fracture), and, with recent linkage of primary and secondary care data, gain more information on injury intent and mechanisms.
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