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Scientific Articles   |    
Improved Healing of Large Segmental Defects in the Rat Femur by Reverse Dynamization in the Presence of Bone Morphogenetic Protein-2
Vaida Glatt, PhD1; Micah Miller, BS2; Alan Ivkovic, MD, PhD1; Fangjun Liu, MD, PhD1; Nicola Parry, DVM3; Damian Griffin, MD4; Mark Vrahas, MD2; Christopher Evans, PhD1
1 Center for Advanced Orthopaedic Studies, Beth Israel Deaconess Medical Center, Harvard Medical School, 330, Brookline Avenue, RN-115, Boston, MA 02215. E-mail address for V. Glatt: vglatt@bidmc.harvard.edu
2 Harvard Orthopaedic Trauma Service, Harvard Medical School, Massachusetts General Hospital, 55 Fruit Street, Boston, MA 02114
3 Division of Comparative Medicine, Massachusetts Institute of Technology, Building 16, Room 825, 77 Massachusetts Avenue, Cambridge, MA 02139
4 Department of Orthopaedic Surgery, Warwick University Medical School, Coventry CV4 7AL, United Kingdom
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Investigation performed at the Center for Advanced Orthopaedic Studies, Beth Israel Deaconess Medical Center, Boston, Massachusetts



Disclosure: One or more of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of an aspect of this work. In addition, one or more of the authors, or his or her institution, has had a financial relationship, in the thirty-six months prior to submission of this work, with an entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. No author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.

Copyright © 2012 by The Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2012 Nov 21;94(22):2063-2073. doi: 10.2106/JBJS.K.01604
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Abstract

Background: 

Large segmental defects in bone do not heal well and present clinical challenges. This study investigated modulation of the mechanical environment as a means of improving bone healing in the presence of bone morphogenetic protein (BMP)-2. Although the influence of mechanical forces on the healing of fractures is well established, no previous studies, to our knowledge, have described their influence on the healing of large segmental defects. We hypothesized that bone-healing would be improved by initial, low-stiffness fixation of the defect, followed by high-stiffness fixation during the healing process. We call this reverse dynamization.

Methods: 

A rat model of a critical-sized femoral defect was used. External fixators were constructed to provide different degrees of stiffness and, importantly, the ability to change stiffness during the healing process in vivo. Healing of the critical-sized defects was initiated by the implantation of 11 μg of recombinant human BMP (rhBMP)-2 on a collagen sponge. Groups of rats receiving BMP-2 were allowed to heal with low, medium, and high-stiffness fixators, as well as under conditions of reverse dynamization, in which the stiffness was changed from low to high at two weeks. Healing was assessed at eight weeks with use of radiographs, histological analysis, microcomputed tomography, dual x-ray absorptiometry, and mechanical testing.

Results: 

Under constant stiffness, the low-stiffness fixator produced the best healing after eight weeks. However, reverse dynamization provided considerable improvement, resulting in a marked acceleration of the healing process by all of the criteria of this study. The histological data suggest that this was the result of intramembranous, rather than endochondral, ossification.

Conclusions: 

Reverse dynamization accelerated healing in the presence of BMP-2 in the rat femur and is worthy of further investigation as a means of improving the healing of large segmental bone defects.

Clinical Relevance: 

These data provide the basis of a novel, simple, and inexpensive way to improve the healing of critical-sized defects in long bones. Reverse dynamization may also be applicable to other circumstances in which bone-healing is problematic.

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    Accreditation Statement
    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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