Implant failure of pedicle screws in long-segment posterior cervical fusion is likely to occur at C7 and is avoidable by concomitant C6 or T1 buttress pedicle screws.

The aim of this study was to investigate the incidence and characteristics of implant failure in posterior cervical long-segment fusion surgery. We retrospectively reviewed 51 cases of posterior cervical long-segment fusion surgery that used pedicle screws, lateral mass screws, or laminar screws. The cranial end of the fusion was C2 or C3, and the caudal end of the fusion was C7 or T1. All patients were observed with CT scans at 6 months postoperatively. We evaluated the loosening and breakage of the implanted screws or rods. In the 51 patients, 257 pedicle screws, 9 laminar screws and 233 lateral mass screws were placed. Implant failure occurred in 25 patients (49.0%). Screw loosening was found in 42 screws (8.4%). Screw breakage occurred in 6 (1.2%) screws. The implant failures were particularly observed in both ends of the fusion level. When C7 was the end of the lower instrumented level, the incidence was 40% without C6 pedicle screws, 33% with unilateral C6 pedicle screws, and 0% with bilateral C6 pedicle screws. The present study revealed that the incidence of implant failures of the screws in long-segment posterior cervical fusion surgery was higher, especially in the caudal end of the fusion levels. In cases where C7 was the lowest instrumented vertebra, buttress screw insertion to C6 is recommended to avoid implant failure of C7 pedicle screws.