The effects of the placement of osteotomy site on osteogenesis during
monofocal and bifocal lengthening were investigated in 37 immature rab
bits allocated to 4 groups according to osteotomy site: (1) monofocal
in the proximal diaphysis; (2) monofocal in the distal diaphysis: (3)
bifocal in the proximal and distal diaphysis; and (4) bifocal in the p
roximal diaphysis, The right tibia was distracted at an overall rate o
f 1.0 mm per day for 15 days, These groups were compared by assessment
of soft radiograph findings and torsional strength 2 and 6 weeks afte
r the end of distraction, Microangiography was done in 5 rabbits in th
e bifocal proximal and distal group, The proximal distracted site show
ed favorable bone regeneration compared with the distal site, and tors
ional strength was significantly greater in the proximal than in the d
istal osteotomy group, Less bone formation and lower torsional strengt
h were observed in the bifocal proximal diaphysis group, with short in
termediate segment, than that in the other bifocal group, with long in
termediate segment, The nutrient artery in the latter group was preser
ved in the intermediate segment and reanastomosed to the metaphyseal a
rteries, These results suggest that the proximal diaphysis is more sui
table for the osteotomy site than is the distal diaphysis, In a 2-leve
l osteotomy, the inflow site of the nutrient artery should be included
within the intermediate segment.