Comparison of gene expression of tissue inhibitor of matrix metalloproteinase-1 between continuous and intermittent distraction osteogenesis: a quantitative study on rabbits

The effect of altering the mechanical loading environment on the expression of bone regenerating molecules in cases of distraction osteogenesis

Distraction osteogenesis (DO) is a surgical technique where gradual and controlled separation of two bony fragments following an osteotomy leads to the induction of new bone formation in the distracted gap. DO is used for limb lengthening, correction of bony deformities, and the replacement of bone loss secondary to infection, trauma, and tumors. Although DO gives satisfactory results in most cases, one major drawback of this technique is the prolonged period of time the external fixator has to be kept on until the newly formed bone consolidates thus leading to numerous complications. Numerous attempts at accelerating bone formation during DO have been reported. One specific approach is manipulation of the mechanical environment during DO by applying changes in the standard protocol of distraction. Attempts at changing this mechanical environment led to mixed results. Increasing the rate or applying acute distraction, led to poor bone formation in the distracted zone. On the other hand, the addition of compressive forces (such as weight bearing, alternating distraction with compression or by over-lengthening, and then shortening) has been reported to increase bone formation. It still remains unclear why these alterations may lead to changes in bone formation. While the cellular and molecular changes occurring during the standard DO protocol, specifically increased expression of transforming growth factor-β1, platelet-derived growth factor, insulin-like growth factor, basic fibroblast growth factor, vascular endothelial growth factor, and bone morphogenic proteins have been extensively investigated, the literature is sparse on the changes occurring when this protocol is altered. It is the purpose of this article to review the pertinent literature on the changes in the expression of various proteins and molecules as a result of changes in the mechanical loading technique in DO and try to define potential future research directions.

Osteodistraction of mandibles with a small bone defect at the planned osteotomy site: a histological pilot study in dogs

AIM

To develop a treatment plan for cases in which a bone defect is located on the osteotomy line of mandibular osteodistraction (DO).

SUBJECTS AND METHODS

Bilateral DO was performed in 17 Mongrel dogs. Prior to surgery, the 34 hemi-mandibles were randomly allocated to three groups: C (n = 10; a standard DO was performed), D - G (n = 12; a bone defect was created on the DO osteotomy line), and D + G (n = 12; the bone defect on the osteotomy line was grafted). After one week of latency, 8 days of distraction, and 4 weeks of consolidation the animals were sacrificed, and the newly formed bone were examined.

RESULTS

In group C, two zones of immature trabecular bone originating from host bone margins were separated by a central fibrous zone. In group D + G uniform new bone formation of the entire distraction gap was observed. In group D - G the distraction gap was mainly filled with fibrous tissue. The values for the newly formed bone volume and trabecular thickness were not significantly different between groups D + G and C, but were higher than values in group D - G (p < 0.05).

CONCLUSION

When a mandibular defect is located at the site of distraction osteotomy, DO can be performed simultaneous with bone grafting of the defect.