Bone Mass Changes in Weight-Loaded and Unloaded Skeletal Regions Following a Fracture of the Hip

Abstract

Higher bone mineral density (BMD) has been reported in weight-loaded skeletal regions and lower BMD in unloaded regions in active athletes compared with controls. These discrepancies remain the first decades after cessation of active careers in former athletes with no remaining discrepancies found after age 65 years compared with ageand 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 regions following a fracture of the hip it is not known. A BMD increase in an unloaded region would support the hypothesis of discrepancies in BMD response to physical activity in loaded and unloaded skeletal regions. BMD (g/cm₂) was measured longitudinally using dual Xray absorptiometry (DXA) in 32 women, 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 unloaded 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 months and 3.7% ± 0.9% the first 13 months after the fracture (P > 0.05 and 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, respectively). In summary, in this longitudinal study, BMD increased in an unloaded skeletal region and decreased in a weight-loaded region following a hip fracture with reduced activity level, suggesting that loaded and unloaded skeletal regions confer different BMD response after changed activity level.