Fractures And Healthy Bones In Children

Osteoporotic fractures are a major public health problem in the elderly. However, fractures have a bimodal peak and are also common in younger life based on the few population-based studies performed to date. Peak incidence rates in children in Tasmania are comparable to those reported in elderly men and women. The upper limb is most frequently involved comprising about two thirds of fractures. Of these forearm fractures are the most common with a female child having a 15% chance and a male child a 22% chance of having this fracture type before twenty years of age. The timing of peak fracture incidence is between 5-14 years in females but estimates vary widely in males. For distal forearm fractures, studies have been more consistent at age 9-12 years in females and 11-14 years in boys. Virtually all childhood fracture types are more common in boys. From a recent fracture case control study of upper limb fractures in southern Tasmania, this would appear to be due to sex differences in the effect of sports participation on fracture risk and higher risk taking behaviour in boys.

Upper limb fractures generally have a definite age peak. Humeral fractures tend to peak first, followed by wrist and forearm fractures and than hand fractures suggesting different fracture specific causes possibly relating to fall characteristics. In the lower limb, virtually all fractures increase during childhood and into the early adult years consistent with trauma being the main cause of these fractures. In Denmark, Sweden and the US, fracture rates for distal forearm fractures have increased substantially in the second half of the twentieth century. Possible reasons for this include changes in physical activity which is closely linked with childhood obesity as well as changes in diet particularly beverage intake. Forearm fracture has been consistently linked with bone mineral density both cross-sectionally and prospectively assessed by dual energy X-ray absorptiometry (DXA) and metacarpal index. The strength of the association is similar to that between hip bone mineral density (BMD) and total fracture risk in elderly subjects with an increase in the odds of fracture of 1.5-1.6 per SD decrease in areal/volumetric BMD or metacarpal index compared to age matched controls. Associations have been inconsistent or negative with total or traumatic fractures, other upper limb fractures and fractures in prepubertal children. In the only prospective study to date, areal BMD was a predictor of new total fractures over a four year follow up period. CT has also been performed in two studies. In the first, when compared to controls, girls with forearm fractures had smaller cross-sectional area in the forearm with a trend to reduced bone density which did not reach statistical significance at any site. This result appears somewhat contradictory to the DXA results as this would imply a stronger association between fracture and areal BMD, which is size dependent, as compared to volumetric BMD. In the second study, Rauch and colleagues describe radial development cross-sectionally and concluded that there was an imbalance between strength and mechanical challenges to the radius during growth because of limited endocortical apposition. This is consistent with a previous report of a transient imbalance between bone mineralisation and linear growth. Non bone factors are also important. New Zealand and US studies have suggested that obese children have a higher risk of wrist and forearm fracture and total fractures possibly due to a higher fall impact and a relative deficit in bone mass. However, no association between body composition and fracture risk was present in Tasmanian children. Instead, there was a dose response association between television watching and wrist and forearm fracture risk and non sports related physical activity was associated with a decrease in fracture risk. Taken as a whole, these results suggest a role of physical inactivity in fracture risk which may not necessarily be dependent on being obese. Somewhat surprisingly, sports participation increased upper limb fracture risk in males and decreased it in females even for the same sports suggesting gender heterogeneity in the approach to sports. Coordination (dynamic balance) has also been linked to wrist and forearm fracture risk while the propensity to take risks was more strongly, but only, associated with hand fracture. Cola beverages have been linked to bone mass and fractures in children in three separate studies. The mechanisms for this association are uncertain. It may be due to milk replacement, an independent effect of cola beverages on fracture risk, lower bone mass or other correlates of cola intake. Calcium intake has been linked with both bone density and fractures in children. However, in Southern Tasmanian children, adjustment for milk intake had little effect on the association between cola intake and fracture. However, unlike other western populations, milk intake has remained higher in Tasmanian children. Breastfed children appear to have higher bone mass at age 8 years and breast milk supplementation leads to gains in bone mass at five years which are not maintained at 12 years. Breastfed children also have a lower risk of total fractures at age 8. It remains to be seen if this persists into the pubertal years when fracture rates are considerably higher. Other dietary factors such as potassium may be important in bone mineralisation and fracture risk in children but studies to date have only been cross-sectional and studied bone density as an intermediate variable.In conclusion, the sheer magnitude of the problem of fracture incidence in children mandates an increased focus on this area. While the evidence for risk factors is increasing and suggests it is possible to design prevention strategies, these associations need to be confirmed in large prospective studies with repeated measures of the putative risk factors.Professor Graeme Jones, MD, FRACPMenzies Research Institute, University of TasmaniaVirtual Rheumatology Centre EAB Member