270 - A Comparison of Subsidence Rates after ACDF Using Structural Allograft...

Oral Posters: Cervical

Presented by: J. Kim - View Audio/Video Presentation (Members Only)


R. Merrill(1), S. Overley(1), D. Leven(1), A. Kumar(1), S. Qureshi(1), J. Kim(1)

(1) Icahn School of Medicine at Mount Sinai, New York, NY, United States


Introduction: Anterior cervical discectomy and fusion (ACDF) is a widely utilized procedure to treat degenerative conditions of the cervical spine. Anterior plating provides added stability to counteract the natural gravitational settling forces that may lead to subsidence of the graft. However, even anterior plates have been shown to undergo significant amounts of subsidence and they have been implicated in post-operative dysphagia due to anterior prominence and esophageal irritation. Stand-alone, zero-profile cages anchor directly into adjacent vertebrae, creating a fixed angle type of device to resist these forces while theoretically reducing rates of post-operative dysphagia due to their zero-profile. The literature is divided, though, as to whether these stand-alone, zero profile cages are as efficacious at preventing significant subsidence as allograft with anterior cervical plating. Our objective with this retrospective study was to compare subsidence over the first 6 months after surgery in those treated with either a stand-alone cage or an anterior cervical plate in ACDF.

Methods: We conducted a retrospective radiographic review of patients who underwent ACDF by a single surgeon at a single center between 2011-2015. Only patients who received either a structural allograft with anterior plating or a stand-alone cage device were included. Any patients without both two week and six-month postoperative lateral cervical radiographs were excluded. Subsidence was determined by the change in posterior vertebral distance (PVD) from endplate to endplate from two weeks to six months. Subsidence was compared statistically between those who received a structural allograft and those who received a stand-alone device by using an unpaired t-test with statistical significance taken at p< 0.05.

Results: We analyzed a total of 36 cases and 55 vertebral levels, with 14 cases and 16 levels in the stand-alone cohort and 22 cases and 39 levels in the structural allograft cohort. The average ages in the stand-alone group and structural allograft group were 46 ± 10 and 51 ± 11, respectively. At 6 months postoperatively, there was no statistical difference (p=0.20) in subsidence of all levels between the stand-alone group (0.61 ± 0.25) and the structural allograft group (0.73mm ± 0.33). When examining single level cases only, there was also no statistical difference (p=0.75) in subsidence between the stand-alone group (0.59mm ± 0.29) and the structural allograft group (0.65mm ± 0.41).

Conclusion: Our results demonstrate that stand-alone cages trend towards lower rates of subsidence at 6 months post-op. Though these subsidence rates were not statistically significant (p=0.20), the stand-alone cage cohort showed less average subsidence over the 6 month investigational period. While affording the potential benefit of less esophageal irritation, the stand-alone cage construct also provides a biomechanically sound construct with equal rates of subsidence as compared to structural allograft with anterior plating.