We investigated the effect of 2-beta-(3-hydroxypropoxy)-1 alpha,25-dihydrox
yvitamin D-3 (ED-71) on the modeling of bone in distraction osteogenesis, T
he tibiae of 30 rabbits were lengthened by 10 mm in 10 days. Following oste
otomy, ED-71 (0.05 mu g/kg) was administered subcutaneously twice a week to
the ED-71 group until necropsy, The bone mineral content (BMC) of the leng
thened callus was measured by dual-energy X-ray absorptiometry (DXA), Five
rabbits per group were killed at 1, 3, and 8 weeks after completion of leng
thening, and the lengthened callus was examined histologically and histomor
phometrically. Bone volume of the lengthened callus was measured by periphe
ral quantitative computed tomography (pQCT) at 8 weeks after the completion
of lengthening. At all timepoints the BMC in the ED-71 group was significa
ntly higher than that in the untreated group. The mineral apposition rate a
nd bone formation rate were higher in the ED-71 group than in the untreated
group at 1 and 3 weeks after the completion of lengthening on the coronal
section, In cross sections, the cortical area and width in the ED-71 group
showed significantly higher values than in the untreated group at 8 weeks a
fter the completion of lengthening, Both the endosteal osteoid surface and
endosteal eroded surface showed no differences between groups. However, the
endosteal mineral apposition rate and endosteal bone formation rate were s
ignificantly higher in the ED-71 group. At 8 weeks after completion of leng
thening, the intracortical area and intracortical BMC were significantly gr
eater in the ED-71 group than in the untreated group, but no significant di
fference was noted in intracortical BMD. These findings indicate that ED-71
increases callus volume during the early period after the completion of le
ngthening, resulting in thick cortical bone formation. (Bone 24:187-193; 19
99) (C) 1999 by Elsevier Science Inc. All rights reserved.