[Study on cervical reasonable range of motion to prevent adjacent segmental intervertebral disc degeneration after...

Objective: To investigate the cervical reasonable range of motion (ROM) after anterior cervical discectomy and fusion (ACDF), so that the intradiscal pressure (IDP) in adjacent segments of the fusion segments did not increase compared with normal cervical spine. Methods: A three-dimensional finite element model of intact cervical spine (C₀-C₇) was established based on CT data from a healthy adult female cervical spine, and its effectiveness was verified. ACDF surgery was simulated at the C₅-C₆ level, with implantation of interbody cage and screw-plate system to construct the ACDF model. A 1.0 Nm moment and 73.6 N follower load was applied to the intact model to determine the normal cervical ROMs. A displacement load was applied to the ACDF model under the same follower load to achieve a total C₀-C₇ ROM equivalent to that of the intact model. The fitting function was employed to calculate the total C₀-C₇ ROM of the ACDF model without increasing IDP in adjacent segments, which was defined as the reasonable ROM. Results: Compared with the intact model, the ACDF model (C_5-6 fusion) demonstrated significantly increased ROM at the adjacent segments C_4-5 and C_6-7 in all motion directions, with an increase of 13.07%-17.77% and 7.78%-18.15%, respectively. The IDP of C_4-5 and C_6-7 increased with increasing total C_0-7 ROM. The IDP of C_4-5 was higher than that of C_6-7 in almost all motion directions, except for extension. Finally, the postoperative reasonable ROMs of ACDF model were 42.4°, 53.6°, 28.6° and 43.0° in flexion, extension, lateral flexion, and axial rotation, which decreased by 6.6%, 3.8%, 3.5% and 5.6% compared with the intact model, respectively. Conclusions: The postoperative reasonable ROM in flexion, extension, lateral bending, and axial rotation is 42.4°, 53.6°, 28.6°, and 43.0°, respectively. Moderately reducing cervical ROM may offset the increase in adjacent segment IDP, thereby providing a novel strategy for preventing adjacent segment disc degeneration after ACDF.