Hypothesis: Young infant bone strength is a multifactorial trait.

Bone strength has been assumed to be relatively similar in young infants born at term. While prematurity has long been known as a risk factor for temporary bone fragility, few other factors have been appreciated that might predispose to young infant bone fragility. Moreover, young infants who present with unexplained fractures are often diagnosed as victims of child abuse based on alleged pathognomonic X-ray findings. However, review of cases of young infants with unexplained fractures often suggests child abuse is unlikely as there is often no bruising or other injuries that would be expected in these infants. The Utah Paradigm is the contemporary model of bone physiology that allows for evaluation of factors that may affect bone strength. Application of the Utah Paradigm to these cases reveals multiple, previously unappreciated, and plausible risk factors to explain the temporary bone fragility in these cases. These risk factors include decreased fetal bone loading from decreased fetal movement, maternal vitamin D deficiency, fetal exposure to drugs that can decrease bone strength, prematurity, hypermobile Ehlers Danlos Syndrome, and gestational diabetes mellitus. It is thus concluded that young infant bone strength is a multifactorial trait. Infants with unexplained fractures and bone fragility from these risk factors in which child abuse is unlikely have a recently described condition called metabolic bone disease of infancy.