You have asked a very good question. The question here really is how 'easily' did your son get this greenstick fracture? Was it due to a very slight fall or was there a significant fall or injury that led to his fracture. The usual time that the cast is left on a child's arm with this kind of fracture is 4 weeeks. If you think that a trivial injury caused your son's fracture it is worthwhile taking him to see your paediatrician for testing for osteogenesis imperfecta.A good start here would be to look carefully at the Xrays taken of your son's arm.
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