Skeletal age will be determined by standardized bone age radiographs of the left wrist which will be performed at the SL site Department of Radiology on the same day as the DXA scans. The sex-specific standards for bone age using plain films of the hand and wrist from the Atlas of Greulich and Pyle will be used as the standard reference (Greulich and Pyle 1959). A single pediatric radiologist, who will be blinded to the age and treatment status of the subjects, will read all bone age radiographs.