Effect of cervical artificial disc replacement on adjacent inferior intervertebral space stress

Purpose: The aim of this study was to investigate the effects of C_5/6 cervical artificial disc replacement (CADR), discectomy and intervertebral fusion on adjacent inferior (C_6/7) intervertebral space stress, and provide a basis for application of CADR. Methods: Eleven fresh-frozen multisegmental (C₃-T₁) cervical spine specimens from healthy adults were studied. For analysis of stress on the adjacent inferior (C_5/6) segment, they were divided into intact group, discectomy group, CADR group and interbody fusion group. The axial load (25-150 N) was exerted on each group. The changes of the adjacent inferior (C_6/7) intervertebral space stress were observed. Results: The adjacent inferior intervertebral space stress in the CADR group was near to that of the intact group, without significant difference (p > 0.05). The stress in the discectomy group was significantly higher than in the intact group, and lower than in the interbody fusion group (p < 0.05 and p < 0.01, respectively). The stress in the interbody fusion group was significantly higher than in the intact and CADR groups, respectively (p < 0.01). Conclusion: The intervertebral fusion and intervertebral disc discectomy can significantly affect the adjacent inferior intervertebral space stress. There is no obvious effect of CADR on adjacent inferior intervertebral space stress.