Background: Segmental bone defects can be
treated with immediate limb-shortening followed by monofocal or bifocal
distraction osteogenesis. In the present study, the efficacy of
monofocal distraction osteogenesis was compared with that of bifocal
distraction osteogenesis in a rabbit model.
Methods: Twenty-four skeletally mature New Zealand White
rabbits were divided into two equal groups: one group had monofocal
distraction osteosynthesis, and the other had bifocal distraction
osteosynthesis. In both groups, a one-centimeter-long segment of
bone was resected from the midpart of the tibial shaft. In the monofocal
reconstruction group, the limb was immediately shortened to close
the segmental defect and the defect was allowed to heal for ten
days. Lengthening was then begun at this site, with use of a specially
designed external fixator, at a rate of 0.5 millimeter per twelve
hours. In the bifocal reconstruction group, the segmental defect
was closed immediately and the fragments were fixed with microplates.
A subperiosteal osteotomy was performed proximal to the tibiofibular
junction, and lengthening was performed at the site of the osteotomy.
The animals in both groups were killed twenty days after the lengthening
was completed. New-bone formation then was evaluated with use of
radiographs, densitometry, biomechanical testing, and histological and
Results: Osseous consolidation occurred in all
but one of the animals. Biomechanical testing demonstrated that
the tibiae that had been treated with use of the simple monofocal
reconstruction technique tended to have greater torsional stiffness
(p = 0.14) and strength (p = 0.09). Follow-up radiographs revealed
that both groups had a significant decrease in radiolucent area
(p < 0.05), which occurred at essentially the same rate after
lengthening. No significant differences were found between the groups
with respect to new-bone mineral density, new-bone area, or the
amount of callus. Thus, after resection of a diaphyseal bone segment
comprising 10 percent of the original length of the tibia and acute
shortening, limb reconstruction was completed successfully through
distraction osteogenesis with use of either a monofocal or a bifocal technique
Conclusions: In the present study, both monofocal
and bifocal techniques of shortening and distraction osteogenesis
were effective for the reconstruction of segmental bone defects.
Under some conditions, the monofocal method may provide a simpler
means of treating such defects.
Clinical Relevance: Damage to the soft-tissue
envelope as well as venous and lymphatic stasis impose limits on
the amount of limb-shortening that can be achieved with use of the
monofocal method and also influence the indications for this procedure
in the clinical setting.