Genetically Modified Marrow Cells Enhances Spine Fusion

· (a – National Institutes of Health [NIH])

Purpose: To investigate the feasibility of using genetically modified marrow cells to enhance allograft spine fusion.

Methods: Lewis rats (n=42) underwent bilateral single level posterolateral spine fusion by implantation of freeze-dried allogenic bone and singeneic bone marrow cells genetically modified by adenovirus encoding bone morphogenetic protein 7 (BMP-7) or as controls AdNull (no transgene), or non-infected cells. To detect new bone formation, xylenol orange was injected 4d prior to sacrifice. Spine fusion was assessed by radiography, manual palpation, mechanical test, and histology 8 wks after surgery.

Results: Bilateral bony bridging was evident in high-resolution radiographs of 70% of AdBMP-7-treated spines vs 0% of controls. Manual palpation showed mechanical fusion in 80% of AdBMP-7-treated spines vs 0% of controls. Fused, AdBMP-7 treated spines were mechanically more stable with a 2.5-3 fold decreased range of motion than controls (p<0.001). Microscopic examination of interspaces of transverse processes in AdBMP-7 treated spines showed the presence of continuous fusion mass with normal trabecular morphology and intense xylenol orange labeling, indicating active bone formation. In control spines, the transverse process showed little or no uptake of xylenol orange and the interspaces were devoid of bone.

Conclusion: Addition of AdBMP-7-modified cells to allograft bone significantly increased the rate of spine fusion when compared to controls.

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