Load-displacement properties of the normal and injured lower cervical spine in vitro

The objective of this study was to determine which discoligamentous structu res of the lower cervical spine provide significant stability with regard t o different loading conditions. Accordingly, the load-displacement properti es of the normal and injured lower cervical spine were tested in vitro. Fou r artificially created stages of increasing discoligamentous instability of the segment C5/6 were compared to the normal C5/6 segment. Six fresh human cadaver spine: segments C4-C7 were tested in flexion/extension, axial rota tion, and lateral bending using pure moments of +/- 3.5 Nm without axial pr eload. five conditions were investigated consecutively: (1) the intact func tional spinal unit (FSU) C5/6; (2) the FSU C5/6 with the anterior longitudi nal ligament and the intertransverse ligaments sectioned; (3) the FSU C5/6 with an additional 10-mm-deep incision of the anterior half of the anulus f ibrosus and the disc; (4) the FSU C5/6 with additionally sectioned ligament a flava as well as interspinous and supraspinous ligaments; (5) the FSU C5/ 6 with additional capsulotomy of the facet joints. In flexion/extension, si gnificant differences were observed concerning range of motion (ROM) and ne utral zone (NZ) for all four stages of instability compared to the intact F SU. In axial rotation, only the stage 4 instability showed a significantly increased ROM anti NZ compared to the intact FSU. For lateral bending, no s ignificant differences were observed. Based on these data, we conclude that flexion/extension is the most sensitive load-direction for the tested disc oligamentous instabilities.