Anterior Cervical Discectomy and Fusion

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Abstract
An animal model for three–level anterior carvical discectomy and fusion was established in the goat. Twenty–one goats underwent surgery, with seven goats in each of three experimental groups. In Group I, all seven goats underwent three–level anterior cervical discectomy without fusion. In Group II, each of the seven goats had a three–level anterior cervical discectimy with autogenous bone performed according to the Smith–Robinson technique. In Group III, fresh–frozen allograft bone was used for each of the three–level discectomy and fusion. Each goat was then killed after 12 weeks. Analysis consisted of radiographic review, fluorochrome labelling, biomechanical rigidity and flexion and extension, axial compressive load, and torsion. Histologic analysis was also performed for evidence of fusion and vertebral body histomorphometric analysis. The analysis of results showed that radiographic union was judged to have occurred in 0 of 21 Group l disc spaces, 10 of 21 Group II disc spaces, and 8 of 21 group III disc spaces. Histologic fusion was judged to have occurred in 0 of 21 Group I goats, 10 of 21 Group II goats, and 0 of 21 Groups III goats. The histologic fusion rate was significantly higher in Group II that either Group I or Group III. Biomechanically, the spines that had autogenous bone grafting (Group II) were significantly stiffer in compressive axial load and in extension. Both Group II and Group III were stiffer in fiexion than Group I. An evaluation of the peri–endplate vascularity showed that the vascularity measured 10.4% in Group I, 16.7% in Group II, and 8.5% in Group III. This was significantly Greater in Group II than in either Group I or Group III. In addition, qualitative analysis of the fluorochroem labelling showed that the autografts had revascularized by 6 weeks in all specimens, whereas only 1 of 21 allograft specimens had revasularized by 6 weeks. By 9 weeks, the allografts had revascularized. In this model using three–level anterior cervical discectomies and fusions, the authors found that autograft bone led to a significantly higher rate of union that did allogtaft bone. We believe that the increased rate of union with autograft bone is partly due to an increased vascular respinse to this bone. This study supports the use of autogenous iliac crest bone grafting over allograft bone grafting for cervical spine fusions.

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