In Vitro Biomechanical Evaluation of Interbody Fusion Cage for Anterior Cervical Fusion in a Caprine Model

Cervical interbody fusion cages (CIFC) are currently used for anterior cervical fusion. There are few reports documenting their biomechanical property in the cervical spine. The purpose of the present study is to investigate biomechanical stability of the caprine cervical spine implanted with a CIFC device. Thirty-two spinal units (C3-4 and C5-6) were harvested from 16 fresh-frozen caprine cervical spines. Each spinal unit underwent discectomy and transection of the posterior longitudinal ligament, and then was implanted with single CIFCs, double CIFCs, autograft, or autograft and anterior cervical plate. An iliac crest tricortical bone was used as an autograft. The degrees of displacement of the cervical spine specimens by multidirectional moments in flexion, extension, lateral bending and axial rotation were evaluated using a video-recording. The stiffness against the multidirectional loads was calculated from load-displacement curves. There were no statistical differences in stiffness between the single-cage and autograft groups in flexion, extension and axial rotation. The autograft group showed significantly increased stiffness compared with that of the single-cage group in lateral bending. The stiffness values were far larger in both the double-cage and autogtraft with plating groups than in the other groups in all directions. There were no statistical differences in stiffness between the double-cage and autogtraft with plating groups in flexion, lateral bending and axial rotation. The double-cage group showed significantly decreased stiffness compared with that of the autograft with plating group only in extension. The stiffness values of the single- or double-cage groups would represent the characteristic biomechanical properties derived from the structure and shape of the implants.