Dynamic Fusion Process in the Anterior Cervical Discectomy and Fusion with Self-Locking Stand-Alone Cages.

Background: Self-locking stand-alone cages can achieve satisfactory clinical results and fusion rate. However, there have been no reports on the causes and relationship of different fusion state. This study is to classify the different fusion states of the index level and to explore the potential contributing factors and links of them.
Methods: From June 2008 to October 2011, 42 patients underwent anterior cervical discectomy and fusion with MC+ cages. More than 5 years' follow-up was reviewed. The fusion state and the relevant clinical and radiologic records were reviewed retrospectively.
Results: At the last follow-up, the fusion proportion of type I, II, III, and IV was 11.7%, 16.9%, 26.9%, and 42.9%, respectively. The overall fusion rate was 97.4%. For all the fused types, significant improvement for the visual analog scale, Japanese Orthopaedic Association, and Neck Disability Index scores was found at the last follow-up (P < 0.05). However, there were no significant differences between the 4 types (P > 0.05). For sagittal vertical axis, type IV was significantly larger than that of type I, II, and III (P < 0.05), and for range of motion, type III was significantly larger than that of type II and IV (P < 0.05).
Conclusions: For anterior cervical discectomy and fusion with self-locking stand-alone cages, the fusion of the index level seems to be a progressive dynamic process during the mid-term follow-up, which may be influenced by the location of the cage, the aagittal vertical axis of the index level, and the global range of motion of the cervical spine. Satisfactory clinical results could be achieved by all the fused types.
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