Effect of different heights of artificial cervical disc replacement on the range of motion of the treated segment

Abstract

Objective To explore the variation of the range of motion(ROM)of operative level after different heights of artificial cervical disc replacement, and to provide guidance for clinical work in selecting appropriate height of artificial cervical disc prosthesis. Methods The preoperative cervical anteroposterior and lateral X-rays of 9 fresh male cadaveric cervical spine specimens were obtained to measure the intervertebral height of C5-6, and 3 screened specimens with the height of about 5 mm were included in the experiment. The experiment was designed to test self-control, and other four groups of cervical specimens including intact group, appropriate height(5 mm)of C5,6 artificial cervical disc replacement group, 1mm increased(6 mm)group and 2 mm increased(7 mm)group were made biomechanical test sequentially. The specimens were fixed to the cervical three-dimensional movement machine, with a 75 N follower load and pure moments of 2 Nm for flexion/extension、left/right bending and left/right axial rotation, to measure the ROM of operative level under the condition of changes in 0.2 Nm/s. Results There were no significant differences in the ROM of flexion/extension, lateral bending and axial rotation between 5 mm group and intact group; the ROM of flexion/extension、lateral bending and axial rotation in 6 mm group increased compared with 5 mm group, but the difference was not statistically significant; the ROM of flexion/extension in 7 mm group was significantly less than that of intact, 5mm and 6 mm group(9.5°±1.0° vs 12.5°±0.9°、11.3°±0.8°、11.6°±0.9°), but significantly greater in axial rotation than 6 mm group(10.4°±1.4°vs 8.6°±0.3°), and there was no significant difference in lateral bending compared with other 3 groups. Conclusion 2 adjacent heights of cervical disc prostheses are implantedsuitably when testing the mold of disc prosthesis , the choice of cervical disc prosthesis with 1 mm increased can improve the ROM of operative level to some extent; while the height with 2 mm increased can lead to the ROM of flexion/extension at the operative level reduced, but the ROM of rotation shows an increasing trend. Key words: Total disc replacement; Biomechanics; Range of motion