Subsidence after Anterior Cervical Interbody Fusion Using a Zero-Profile Device

Corresponding author: Pyung-Goo Cho Department of Neurosurgery, Ajou University Medical Center, Ajou University College of Medicine, 164, World cup-ro, Yeongtong-gu, Suwon 16499, Republic of Korea Tel: +82-31-219-7808 Fax: +82-31-210-5236 E-mail: nsdrcpg@ajou.ac.kr Objective: Zero-profile device (Zero-P) has generally been used as a stand-alone cage in anterior cervical discectomy and fusion (ACDF). However, using Zero-P has been reported to be associated with a high subsidence rate. The present study evaluates the factors that influence the subsidence of ACDF. Methods: Records of a total of 29 patients with degenerative spondylosis resulting in radiculopathy or myelopathy between C2 and C7 who underwent ACDF with Zero-P were retrospectively reviewed. The participants received 1 or 2 level ACDF with Zero-P in our clinic from December, 2011 to December, 2017. A total of 35 treatment levels were included in the analysis. Subsidence was defined when anterior segmental heights decreased by more than 2 mm during the follow-up period. The patients were divided into the subsidence and non-subsidence groups. The following factors were investigated in relation to the occurrence of subsidence: age, gender, body mass index, diabetes mellitus, cage height, perioperative distraction, segmental lordosis, pain score, fusion grade, anterior/posterior segmental height ratio, and cage distance. Results: Cage subsidence was observed in 15 cases (15/35, 42%). Cage distance at immediate postoperation was significantly different between the 2 groups; specifically, while the group with subsidence had 2.66±1.62 mm distance, the group without subsidence had 1.24±1.13 mm distance (p=0.008). Conclusion: This study confirms that the more deeply titanium part is inserted at the anterior edge, the more subsidence occurs. In order to decrease the occurrence of cage subsidence, Zero-P cages should be located the closest possible to the anterior rim of vertebral body at operation.