The main results of this study confirm a greater prevalence of overweight/obesity in children and adolescents with a recent fracture compared to age and gender matched fracture-free children, but indicate different patterns related to gender and site of fracture. Overweight/obesity rate was increased in girls with fracture either at the upper or the lower limb, while it was increased only in boys reporting a fracture at the lower limb.
While obesity in the adult population has been found to be an independent risk factor of trauma-related morbidity, but not of fractures [5
], fractures have been enlisted among orthopaedics complaints of childhood obesity [6
]. In pediatric trauma patients, obese children had a higher incidence of extremity fractures and also a higher risk for certain complications [8
]. The reasons for increased numbers of fractures in the obese adolescent population are variably questioned. Reduced bone mass may be a predictor of fracture in children [19
], but contradictory results were reported on skeletal mass in overweight/obese children. Since most studies found normal or increased bone mineral content in obese children [20
], the main conclusion was that obese children have decreased bone mass relative to bone size and body weight [19
]. It is believed that the increased bone mineral density in obese adolescents may be not sufficient to overcome the significant greater forces that are generated when an overweight child falls.
The assumption of a greater prevalence of fractures in overweight than non-overweight children derives from a retrospective study carried out by Taylor et al. [7
] on medical charts of overweight and non-overweight children and adolescents. In their study, Authors did not consider the different sites of fractures or gender related differences. Interestingly, female gender prevailed in their study population of overweight patients compared to non overweight participants.
Apart this study, most Authors analysed the association between weight status and upper limb fractures, in particular distal forearm fractures, which indeed represent the most common fractures in childhood [23
]. Our finding of a greater prevalence of overweight/obese subjects among girls with upper limb fractures and in particular with forearm/wrist fractures is confirmed by other studies. Goulding et al. [24
] carried out a case–control study about distal forearm fractures in young girls and observed that girls with fractures tended to be heavier than those without, particularly in the 8–10 years age group. As in our study, they excluded fractures from traffic accidents, but their sample included also trauma from severe dynamics (fall > 3 meters) and a high proportion of patients with recurrent fractures. The same authors in a 4 year follow-up study of fractured and fracture-free girls demonstrated that previous fracture, age, total body bone mineral density but also weight were significant factors predicting the risk of new fracture [25
]. Skaggs et al. [26
] analyzed the skeletal phenotype in low-energy impact fractures of the forearm in girls. At variance with Goulding et al. [24
], they could not be able to find any difference in body mass among girls with and without fractures, since their control population was also matched for height and weight. However, they reported that participants were overall 12 kg overweight when compared with age-adjusted normal percentiles for growth. They proposed that the smaller cross-sectional diameter combined with increased body mass and minor trauma created a predisposition to fracture in these patients. With regard to boys, we did not find any significant difference in the prevalence of overweight/obesity between cases and controls when total fractures, upper limb fractures or elbow/forearm fractures were analyzed. In contrast with our results, Goulding et al. [27
] showed that high BMI tripled the fracture risk (O.R. 3.47, 95% IC 1.69-7.09) in boys who sustained forearm fractures. Although the discrepancy with our results remains unexplained, the male population studied by Goulding, as in the female study, included trauma from severe dynamics and a high proportion of patients with recurrent fractures.
Instead, we found a greater prevalence of overweight/obesity both in girls and boys sustaining lower limb fracture, in particular foot and tight. As far as we are acknowledged on, several studies reported an increased risk of lower extremity injuries (including fractures, dislocations, sprains/strains) in overweight or obese children [28
], while no previous study specifically focused on the association between overweight and lower limb fractures in children. We are only aware of several studies reporting a greater prevalence of ankle fractures in obese adults [29
]. Although the exact biomechanics of lower extremity injuries in overweight children is largely unknown, the extra weight superimposed to the leg and foot in the overweight subject may explain the increased risk of injuries at the lower extremities. Higher prevalence of abnormal lower extremity alignment has been reported in overweight children, explaining the detrimental effect of obesity to the lower extremity [7
]. Poor balance, unstable postural sway, altered kinetic characteristics of locomotion in overweight children could be additional risk factors which involve lower extremities [31
]. The reason why overweight boys may be mainly exposed to the risk of lower limb fracture and not to upper limb fractures is presently difficult to explain, but it could be also viewed in the light of different risk taking behaviours and/or poor intrinsic coordination [33
]. Unfortunately we did not assess movement skills and coordination in our population, therefore no final conclusion can be drawn.
There are no data indicating that overweight children fall more frequently than normal weight peers, while it has been only suggested that they fall with more force and in more ackward position [34
]. We found that prevalence of overweight/obesity did not differ between groups with low or moderate trauma. In both groups the dynamics was represented by falling, while the difference lied in the height of the fall, the landing surface, the physical activity engaged in, and whether or not any equipment was being used. Our data suggest that the greater overweight rate in children with fractures does represent an inherent vulnerability of the obese child and is not related to the characteristics of the fall itself.
Since lifestyle behaviours have been highly associated with fracture risk in children [1
], the role of physical activity and inactivity was analyzed also in our sample. Sports participation as well as TV viewing ≥ 2 hours were significantly higher in cases than controls. Previous studies reported that higher levels of sports participation increase the risk of fracture in children [1
]. This effect, that was independent on the higher bone mineral density and bone size relative to body size determined by the increased volumes of vigorous physical activity [35
], was presumably explained through increased exposure to injuries. In our sample 11.8% fractures occurred from organized sporting activities: soccer was the most common cause of injury (56.6%), followed by roller skating (22.6%). Indeed soccer is one of the most popular activities especially among younger boys in our Country, and has a high rate of low-energy trauma, while roller skating, mainly practiced by girls, may be associated with moderate energy trauma [13
A dose-dependent association between TV, video and computer viewing and wrist/forearm fractures was also reported in children aged 9–16 years [1
]. Inactivity may lead to impaired postural balance and reduced muscular strength and coordination,contributing to an increased risk of falling. TV viewing, the most relevant proxy for sedentary lifestyle, has consistently been found associated with childhood obesity [36
]. In our study TV viewing ≥ 2 hours was greatly prevalent in overweight/obese children with fractures compared to overweight/obese children without fractures.
Interestingly, more TV viewing was related to smaller gains in bone area and bone mass accounting for race, sex, and height in pre-schoolers, while no effect was found by physical activity measured by accelerometer [37
Calcium intake is also a strong determinant of mineral accrual in growing children [38
] and inadequate calcium intake could increase the risk of fracture. Our results did not show any association between dietary intake of calcium and risk of fractures, in agreement with previous reports [35
The strength of the present study is based on the fact that we provided objective measurements of height and weight (hence, the accurate estimate of BMI) rather than self-reported height and weight, which is a potential source of error caused by reporting bias. Moreover all fractures were confirmed radiographically and the dynamics of trauma was accurately ascertained. Our study also has a limitation in the lower sample size of hospitalized controls. This was due to the difficulty of enrolling the control population, mainly girls, from the same setting (hospital) of the case population. Notwithstanding this limitation, the prevalence of overweight/obesity observed in our control population (boys 51.8%, girls 31.9%) reflects the overweight/obese prevalence indicated by the Health Behaviour in School Children survey performed in 2009–2010 in our region (boys 45%, girls 28% at 11 years of age) [40
], according to the definition used by the International Obesity Task Force [11