Regional variations in the progression of bone loss in two different mouse osteopenia models

Differences in trabecular and cortical bone loss have been demonstrated clinically, but differences in bone loss at different skeletal sites remain unclear. We examined regional variations in bone loss histomorphometrically in two strains of mice in which osteopenia progresses spontaneously: tiptoe-walking Yoshimura (twy) mice (from 4 to 37 weeks of age) and senescent ICR mice (from 4 to 88 weeks of age). Morphometrical measurements were obtained to investigate the changes with age in trabecular bone area and anterior cortical bone width in the lumbar vertebral body, trabecular bone area in the tibia, bone area in the parietal bone, and the cortical index in the humerus. Results showed that, in twy mice, trabecular turnover was higher than in ICR mice, and bone loss progressed in the following order: tibial trabecular bone, lumbar trabecular bone, parietal bone, lumbar anterior cortical bone, and the humerus. In ICR mice, bone formation declined after 60 weeks. Bone loss progressed in tibial trabecular bone and the parietal bone at 60 weeks of age, followed by lumbar trabecular bone, lumbar anterior cortical bone, and the humerus at 88 weeks of age. Bone loss varied at each site and between the two mouse strains, with different bone turnover rates. The findings of the present study indicate that special attention should be paid to regional variations in the progression of bone loss associated with differences in pathologic features.