Bone mass changes in weight-loaded and unloaded skeletal regions followinga fracture of the hip

Higher bone mineral density (BMD) has been reported in weight-loaded skelet al regions and lower BMD in unloaded regions in active athletes compared wi th controls. These discrepancies remain the first decades after cessation o f active careers in former athletes with no remaining discrepancies found a fter age 65 years compared with age- and gender-matched controls. Physical activity is reduced after a hip fracture and BMD decreases in weight-loaded skeletal regions following the injury. If BMD increases in unloaded region s following a fracture of the hip it is not known. A BMD increase in an unl oaded region would support the hypothesis of discrepancies in BMD response to physical activity in loaded and unloaded skeletal regions. BMD (g/cm(2)) was measured longitudinally using dual Xray absorptiometry (DXA) in 32 wom en. mean age 77 years (range 57-90) and 12 men, mean age 74 years (range 53 -89) with a hip fracture, the upper part of the skull representing an unloa ded skeletal region, the arms a partly loaded region, and the femoral neck a weight-loaded region. Measurements (mean) were done in 11 days, 5 months, and 13 months after the hip fracture. Data are presented as mean +/- SEM. BMD increased in the upper part of the skull by 1.9% +/- 0.8% the first 5 m onths and 3.7% +/- 0.9% the first 13 months after the fracture (P < 0.05 an d P < 0.001, respectively). BMD did not change in the arms but decreased in the nonfractured femoral neck by 4.7% +/- 1.8% the first 5 months and 4.5% +/- 1.7% the first 13 months after the fracture (both P < 0.01, respective ly). In summary, in this longitudinal study, BMD increased in an unloaded s keletal region and decreased in a weight-loaded region following a hip frac ture with reduced activity level. suggesting that loaded and unloaded skele tal regions confer different BMD response after changed activity level.