Bone mineral density and fractures in boys with Duchenne muscular dystrophy

The relationships between bone density, mobility, and fractures were assess ed in 41 boys with Duchenne muscular dystrophy. Bone density in the lumbar spine was only slightly decreased while the boys were ambulatory (mean z-sc ore, -0.8), but significantly decreased with loss of ambulation (mean z-sco re, -1.7). In contrast, bone density in the proximal femur was profoundly d iminished even when gait was minimally affected (mean z-score, -1.6), and t hen progressively decreased to nearly 4 standard deviations below age-match ed normals (mean z-score, -3.9). These are consistent with the findings tha t 18 (44%) of the boys sustained a fracture, 66% of these fractures involve d the lower extremities, and there were no spinal compression fractures. Fu rthermore, four (44%) of nine boys who were walking with aids or support at the time of fracture never resumed walking after the fracture. Osteoporosi s is most profound in the lower extremities of boys with Duchenne muscular dystrophy, and begins to develop early while still ambulating. Frequent fra ctures that may result in loss of ambulation are the clinical consequences.