[Biomechanical research on morphometric changes in adjacent inferior cervical intervertebral foramen after artificial disc replacement].

OBJECTIVE: To explore changes in the height and width of the cervical intervertebral foramina of C6.7 before and after the C5.6 discetomy, the replacement or the anterior intervertebral fusion so as to provide the theoretical basis for the clinical practice.

METHODS: Eleven fresh cervical spinal specimens were obtained from young adult cadavers. The specimens of C5.6 were divided into the integrity group, the discectomy group, the artificial disc replacement group, and the intervertebral fusion group. The range of variety (ROV) of the C6.7 intervertebral foramen dimensions (height, width) before and after the loading tests (0.75, 1.50 Nm) were measured in the 4 groups.

RESULTS: The C6.7 intervetebral foramen height and width increased significantly during flexion (P < 0.01) but decreased significantly during extension (P < 0.01). There was a significant difference between the two test conditions in each of the 4 groups (P < 0.01). However, in the two test conditions there was no significant difference in ROV of the C6,7 intervetebral foramen height and width during flexion and extension between the integrity group, the discectomy, and the artificial disc replacement group (P > 0.05), but a significant difference in the above changes existed in the intervertebral fusion group when compared with the other 3 groups (P < 0.05). In the same group and under the same conditions, the ROV of the C6.7 intervetebral foramen height and width was significantly different in the two test conditions (P < 0.01).

CONCLUSION: The results have indicated that artificial disc replacement can meet the requirements of the normal cervical vitodynamics. The adjacent inferior cervical intervetebral foramen increases during flexion but decreases during extension. The intervertebral fusion is probably one of the causes for the cervical degeneration or the accelerated degeneration and for the cervical spondylotic radiculopathy and the brachial plexus compression.