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Distraction Osteogenesis After Acute Limb-Shortening for Segmental Tibial Defects Comparison of a Monofocal and a Bifocal Technique in Rabbits*
Rainer H. Meffert, M.D.†; Nozomu Inoue, M.D., PhD.; John E. Tis, M.D.‡; Erwin Brug, M.D.§; Edmund Y. S. Chao, Ph.D.†
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Investigation performed at the Department of Orthopaedic Surgery, Orthopaedic Biomechanics Laboratory, The Johns Hopkins University, Baltimore, Maryland
*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Funds were received in total or partial support of the research or clinical study presented in this article. The funding sources were the Max-Kade Foundation, New York, and Orthofix, Limited, Verona, Italy. The external fixators were provided by Orthofix, Limited, Verona, Italy, and the microplates were provided by Howmedica Leibinger, Pfizer Medical Technology Group, Dallas, Texas.
†Department of Orthopaedic Surgery, Orthopaedic Biomechanics Laboratory, The Johns Hopkins University, Ross Research Building, 720 Rutland Avenue, Room 235, Baltimore, Maryland 21205-2196.
‡Orthopaedic Surgery Service, Walter Reed Army Medical Center, Washington, D.C. 20307.
§Department of Trauma and Hand Surgery, University of Münster, Waldeyerstrasse 1, D-48129 Münster, Germany.

J Bone Joint Surg Am, 2000 Jun 01;82(6):799-799
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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 histomorphometric analysis.

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 in rabbits.

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.

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    These activities have been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint sponsorship of the American Academy of Orthopaedic Surgeons and The Journal of Bone and Joint Surgery, Inc. The American Academy of Orthopaedic Surgeons is accredited by the ACCME to provide continuing medical education for physicians.
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