Degenerative Cervical Disc Disease: Long-term Changes in Sagittal Alignment and Their Clinical Implications After Cervical Interbody Fusion Cage Subsidence A Prospective Study With Standalone Lordotic Tantalum Cages

Study Design: A retrospective, observational study of prospectively collected outcomes. Objective: To investigate the long-term clinical course of anterior cervical discectomy and fusion with interbody fusion cages (ACDF-IFC) with lordotic tantalum implants and to correlate the radiologic findings with the clinical outcomes, with special emphasis on the significance and the influence of implant subsidence. Summary of Background Data: Cage subsidence is the most frequently reported complication after ACDF-IFC. However, most reports fail to correlate cage subsidence with lower fusion rates or with unsatisfactory clinical results. Methods: Forty-one consecutive patients with symptomatic degenerative cervical disk disease with failure of conservative treatment were included. All patients underwent 1-/2-level ACDF-IFC with lordotic tantalum implants. The mean follow-up was 4.91 years. Results: The final follow-up fusion rate was 96.96% (32/33). The interspace height (IH) at the affected levels was significantly incremented after implant insertion, and despite a gradual loss in the height over time, the final follow-up IH was significantly higher than that measured preoperatively (P< 0.0001). Anterior IH and posterior IH lost 55.8% and 76.2% of the initially incremented height, respectively, with a final increase of 72% in the AIH-PIH height differential. Implant subsidence (> 3mm) occurred in 11 disk spaces (26.82%). Preoperative and postoperative IH were significantly higher in subsidence patients; however, there was no difference in the final follow-up IH (P> 0.05). Patients with >= 3 years of follow-up (n= 29) did not demonstrate further significant subsidence beyond the second year. Regarding C1-C7 lordosis, the segmental Cobb angle, the cervical Visual Analogue Scale, and Neck Disability Index questionnaires, no difference between patients with or without final follow-up endplate subsidence was encountered. Conclusions: Until fusion occurs, tantalum cage settlement into the vertebral body is to be expected. Further subsidence could be the result of segmental adaptative changes. Graft subsidence did not affect the clinical outcome in any of our patients during long-term follow-up. The occurrence of dynamical implant subsidence had a positive effect on cervical lordosis, especially at the posterior IH.